Journal of Affective Disorders 165 (2014) 24–30
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Research report
The effect of exercise on hippocampal volume and neurotrophines in patients with major depression—A randomized clinical trial Jesper Krogh a,n, Egill Rostrup b, Carsten Thomsen c, Betina Elfving d, Poul Videbech e, Merete Nordentoft a a
Mental Health Centre Copenhagen, Mental Health Services in the Capital Region of Denmark, University of Copenhagen, Copenhagen, Denmark Functional Imaging Unit, Department of Diagnostics, Copenhagen University Hospital, Glostrup Hospital, Denmark c Department of Radiology, Rigshospitalet, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark d Translational Neuropsychiatry Unit, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark e Department for Depression and Anxiety Q, Aarhus University Hospital, Risskov, Denmark b
art ic l e i nf o
a b s t r a c t
Article history: Received 4 January 2014 Received in revised form 15 April 2014 Accepted 15 April 2014 Available online 23 April 2014
Background: The hippocampal volume is reduced in patients with major depression. Exercise leads to an increased hippocampal volume in schizophrenia and in healthy old adults. The effect of exercise on hippocampal volume is potentially mediated by brain derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), and insulin like growth factor 1 (IGF-1). The aim of this trial was to assess the effect of an aerobic exercise intervention on hippocampal volume and serum BDNF, VEGF, and IGF-1 in patients with major depression. Methods: Patients were randomized to an aerobic exercise intervention (n ¼ 41) or a control condition (n ¼38). Both interventions consisted of three supervised sessions per week during a three months period. Results: Post-intervention the increase in maximal oxygen uptake was 3.90 ml/kg/min (SD 5.1) in the aerobic exercise group and 0.95 ml/kg/min (SD 6.2) in the control group (p¼0.03). The hippocampal volume, BDNF, VEGF, or IGF-1 did not differ between the two groups. Post-hoc we found a positive association between change in hippocampal volume and verbal memory (Rho ¼0.27; p¼ 0.05) and change in hippocampal volume and depressive symptoms (Rho ¼ 0.30; p¼0.03). Limitations: Participation was low in both groups corresponding to an average participation of one session per week. Conclusion: Despite a significant increase in maximal oxygen uptake, a pragmatic exercise intervention did not increase hippocampal volume or resting levels of neurotrophines in out-patients with mild to moderate major depression. Trial identifier: ClinicalTrials.gov (NCT00695552) & 2014 Elsevier B.V. All rights reserved.
Keywords: Hippocampus Exercise Depression Neurogenesis Memory BDNF
1. Introduction The hippocampal region is thought to play a pivotal role in major depression. This temporal structure is involved in cognitive skills such as memory, learning, regulation of the hypothalamic–pituitary– adrenal (HPA) axis, and mood (Eisch and Petrik, 2012). Meta-analysis suggests that the bilateral hippocampal volume is reduced 0.3–0.4 standard deviations in patients with depression compared to healthy controls (Videbech and Ravnkilde, 2004). It has been speculated that
n Correspondence to: Mental Health Centre Copenhagen, Bispebjerg Bakke 23, Opg. 13a, DK-2400, Denmark. Tel.: þ45 2553 54 85. E-mail address: [email protected] (J. Krogh).
http://dx.doi.org/10.1016/j.jad.2014.04.041 0165-0327/& 2014 Elsevier B.V. All rights reserved.
the observed reduction in hippocampal volume in patients with depression is due to decreased neurogenesis. Randomised clinical trials suggest that exercise leads to an increased hippocampal volume in healthy old adults (Erickson et al., 2011) while the evidence for schizophrenia is conflicting (Pajonk et al., 2010; Scheewe et al., 2013). Furthermore, in two of these trials the increase in hippocampal volume was positively associated to increased maximal oxygen uptake, brain derived neurotrophic factor (BDNF), spatial and verbal memory (Erickson et al. 2011; Pajonk et al., 2010). Studies on rodents have found that the exercise related increase in memory and learning is mediated through an upregulation of BDNF, which has the ability to stimulate synapticplasticity (Tapia-Arancibia et al., 2004). The exercise induced cell
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proliferation is inhibited by peripheral blockade of either insulin growth factor 1 (IGF-1) or vascular endothelial growth factor (VEGF) (Fabel et al., 2003; Trejo et al., 2008), which indicate that the exercise induced neurogenesis is dependent on not only BDNF but peripheral IGF-I and VEGF. Furthermore, it has been shown that antidepressant treatment up-regulates BDNF in humans (Shimizu et al., 2003) and a relationship between genetic variants of BDNF locus and depression has been implied (Schumacher et al., 2005). On this background, it could be argued that low BDNF levels contribute to the pathophysiology of depression, and that exercise has a beneficial effect on mood and cognitive function in patients with depression through an up-regulation of BDNF, VEGF, and IGF-1. The aim of the present study was to determine if a pragmatic exercise intervention compared to an exercise control condition would increase hippocampal volume and increase serum levels of neurotrophines (BDNF, VEGF, and IGF-1) in patients with major depression.
2. Methods 2.1. Design The study was designed as a randomised, parallel-group, superiority trial with blinded outcome assessment. The trial protocol was approved by the local ethics committee (H-A-2008-046), the Danish Data Protection Agency (J.nr. 2008-41-2354), and registered at ClinicalTrials.gov (NCT00695552). Verbal and written informed consent was obtained from all participants involved in the trial.
2.2. Study population All patients were recruited for participation from the DEMO-II trial, a randomized clinical trial evaluating the antidepressant effect of aerobic exercise (Krogh et al., 2012). The initial 90 consecutively enroled participants were asked to participate in the current sub-study. Eligible participants were men and women between 18 and 60 years of age, referred from a clinical setting by a physician or a psychologist, a diagnose of major depression (DSM-IV) based on the Danish version of the Mini International Neuropsychiatric Interview (Bech et al., 1999). The participants all scored above 12 on the HAM-D17 and were able to comprehend the informed consent statement. Exclusion criteria were current drug abuse, any antidepressant medication within the last two months, current psychotherapeutic treatment, contraindications to physical exercise, regular recreational exercise over 1 h per week, suicidal behaviour according to the 17-item Hamilton Depression Rating Scale (HAM-D17, item 3 over 2), pregnancy, or current/previous psychotic or manic symptoms.
2.3. Randomisation Participants were randomized with a 1:1 ratio to either aerobic exercise or an attention control group. Randomisation was stratified according to severity of depression (high or low depression score; high 417 HAM-D17) and blood pressure (high or low blood pressure; high 4 140/95 mmHg). The randomisation was centralised and carried out by the Copenhagen Trial Unit (CTU) using a computerised randomisation sequence with alternating block sizes (alternating 8, 10, and 12) unknown to the investigators. Prior to the first training session the trial physiotherapist did contact the CTU by phone for participant allocation.
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2.4. Blinding Neither participants nor the physiotherapist conducting the intervention were blinded to the allocation. The outcome assessors (the study nurse, the laboratory and the MRI technicians) were all blinded to participant allocation. Prior to the follow-up interview, participants were instructed not to reveal their allocation to the outcome assessors. The statistical analysis and preparation of the first draft was carried out blinded to group assignments. 2.5. Physical examination For the physical examination, the participants were requested to report at the research department between 8:00 and 10:00 a.m. The participants were instructed not to take any food or liquids except for water beginning from midnight prior to the examination and abstain from strenuous physical activity prior to the examination. Height and weight was measured using an electronic weight (Soehnle Medicals, Type 7700, Backnang, Germany). Blood pressure was measured after 5 min of rest in a sitting position. The mean of three consecutive measurements is reported. To estimate the cardiovascular fitness of the participants a bicycle cardiopulmonary exercise test (Ergomedic 839 e, Monark, Vansbro, Sweden) was used based on Andersen's cycle exercise protocol (Andersen, 1997). 2.6. Intervention After baseline assessment the patients were randomised to either aerobic exercise or a control group as described in detail elsewhere(Krogh et al., 2012). In short, both groups were scheduled to participate in 45 min supervised sessions three times per week in a 3 months programme. In the aerobic training group the participants exercised on stationary bikes at approximately 80% of their maximal heart rate, while the training in the exercise control group was predominantly stretching exercises and low impact exercise such as throwing and catching balls. 2.7. Outcomes 2.7.1. Hippocampal volume The primary outcome for this sub-study was the left and right hippocampal volumes measured post-intervention. Hippocampal volume was estimated using magnetic resonance imaging (MRI). MRI volumetric images were acquired on a 3.0T Siemens system using a T1-weighted 3D gradient MPR sequence with a resolution of 1 1 1 mm with the following parameters: TR ¼2250 ms; TE 3 ms; FoV read ¼256 mm; FoV phase ¼100.0%; and flip angle 91. All images were performed in the coronal plane at an angle perpendicular to the hippocampal long axis. All tracings were manually performed by the same rater (JK) who was instructed by a specialist in neuroimaging (ER). After an initial training period the intra-rater reliability was obtained by estimating the left and right hippocampus of the same 10 patients with at least one day between the first and second estimations. The intraclasscorrelation-coefficient of the first and second assessments was 0.98 (95% CI. 0.91–0.99) and 0.95 (95% CI. 0.82–0.99) for the right and left hippocampal regions. In absolute numbers the median difference between first and second assessments was 12.5 mm3 (IQR 121 to 96) and 129 mm3 (IQR 25–178) for right and left hippocampal volumes. Hippocampus was defined as the cornu ammonis, dentate gyrus, and subiculum. Regions of interest were traced in the coronal plane. Sagittal and axial planes were used continuously to assist tracing in the coronal plane. All estimations of volumes were acquired by tracing regions of interest on each coronal image and finally all slices were added in order to determine the volume.
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For tracing and volume estimation an in house programme was used (RIP, written for Matlab). Border definitions were based on common segmentation protocols (Konrad et al., 2009). The anterior border was located in the sagittal plane. Differentiation of amygdala and hippocampus was based on the alveus. The superior border was identified using alveus as an internal landmark, or the temporal horn of the lateral ventricle as an external landmark. The inferior border was defined as the white matter of the parahippocampal gyrus. The inferomedial border was drawn from the tip of white matter from the parahippocampal gyrus medially to cisterna ambiens. The lateral border was defined by CSF of the lateral ventricle as an external landmark. The posterior border was located where an ovoid grey matter appear inferiomedially to the trigone of the lateral ventricle. Head of the hippocampus was anteriorly identified as described above and posteriorly as the last coronal image where the uncal apex was visible (Malykhin et al., 2007). The total volume of the brain tissue and grey matter was estimated with SIENAX (Smith et al., 2002), part of the FSL software package (2013) (FMRIB Software Library). 2.7.2. Neurotrophic factors Previously, we have shown the BDNF levels in plasma samples, but not in serum or whole blood samples, to be affected by the preanalytical conditions (Elfving et al., 2010). BDNF, VEGF, and IGF1 were all estimated using serum samples collected from an antecubital vein after five minutes of rest and stored at 801 until analysis. Quantification of serum BDNF, VEGF, and IGF-1 levels was performed with the enzyme-linked immunosorbent assay (ELISA) kits. The same batch number was used for the entire experiments of BDNF, VEGF, and IGF-1. The standard curves and the samples were run in duplicate, blinded for case and control. Serum BDNF levels were measured using the Quantikine Human BDNF Immunoassay from R&D Systems (USA). The determination was processed according to the manufacturer's specifications and the absorbance was immediately measured at 450 nm with wavelength correction set to 540 nm (EL 800 Universal Microplate reader, Bio-Tek instruments, INC). For the BDNF measurements the samples were diluted 1:20 to be within the range of the standard curve. The standard curves ranged from 62.5 to 2000 pg/ml BDNF. Three internal BDNF controls (high: 1959–3315 pg/ml, medium: 1099– 1525 pg/ml, low: 344–506 pg/ml), commercial available from R&D Systems (USA), were included on each plate. The serum VEGF levels were measured using the Quantikine Human VEGF Immunoassay from R&D Systems (USA). The determination was processed according to the manufacturer's specifications and the absorbance was immediately measured at 450 nm with wavelength correction set to 540 nm (EL 800 Universal Microplate reader, Bio-Tek instruments, INC). The standard curves ranged from 31.2 to 1000 pg/ml VEGF and the samples were run undiluted to be within the range of the standard curve. Three internal VEGF controls (high: 682–1354 pg/ml, medium: 350–686 pg/ml, low: 115–259 pg/ml), commercially available from R&D Systems (USA), were included on each plate. The serum IGF-1 levels were measured using RayBios Human IGF-1 ELISA kit from RayBiotech, Inc (USA). The determination was processed according to the manufacturer's specifications and the absorbance was immediately measured at 450 nm (EL 800 Universal Microplate reader, Bio-Tek instruments, INC). The standard curves ranged from 0.25 to 60 ng/ml IGF-1 and the samples were run undiluted to be within the range of the standard curve. 2.7.3. Assessment of mood and cognitive function Depression severity was assessed using the Hamilton Depression Rating Scale with 17-items (Hamilton, 1960). Assessment of verbal memory was assessed by the Buschke's Selective Reminding test
(Buschke and Fuld, 1974). A list of 10 different unrelated words was read aloud to the participant. The participant is then asked to recall the list. The interviewer repeats the words that the patient misses and the participant is asked to try again until all ten words can be said, or until ten attempts. The score is the total number of blanks or mistakes; thus, a high score indicates poorer performance. Visuospatial memory was assessed by the Rey's Complex Figure Test (Meyers et al., 1996). In this test the participant was shown a geometrically complex figure on a sheet of paper and asked to copy it to another sheet of paper. When this is done the drawings and the original are put away and after three minutes the participant is asked to draw as much of the figure they can recall. The score is calculated based on the tree-minute recall drawing. A high score reflects better performance. 2.8. Statistics The statistical analysis was based on the intention-to-treat principle including all randomised patients regardless of subsequent withdrawal or deviation from the protocol. Assessment of variables measured at baseline and post-intervention was reported using mean and standard deviation. Post-intervention values were compared using student's t-test for unpaired data. Missing values were imputed using the multiple imputation technique available in SPSS, with 100 imputations and 20 iterations having allocation and baseline values as the predicting variables. Per protocol analysis was undertaken including participants who attended Z50% of the scheduled sessions. All significance tests were 2-tailed and p-values r0.05 were considered significant. Statistical analysis was conducted using SPSS version 19.0 (SPSS, Inc.: Chicago, USA).
3. Results The initial 90 patients included in the DEMO-II trial were considered for enrolment in the current sub-study, as displayed in Fig. 1. The inclusion of patients occurred between September 2008 and April 2010. Eleven patients were excluded from MRI due to either severe claustrophobia (n¼10) or metallic implants (n¼1), leaving 79 participants to constitute the current sample. Forty-one were allocated to the aerobic exercise group and 38 were allocated to the control group. The mean age in the included group was 41.3 (SD 12.1) years and consisted of 53/79 (67.1%) female participants. The mean HAM-D17 was 19.0 (SD 4.3), 32/79 (40.5%) had recurrent depression, and 43/79 (54.4%) generalised anxiety disorder comorbid with their depression. The aerobic exercise group and control group were comparable with respect to baseline demographic and clinical characteristics as displayed in Table 1. 3.1. Compliance The mean attendance was 12.9 (SD 9.6) sessions in the aerobic exercise group compared to 12.4 (SD 8.6) sessions in the control group (p¼0.54) of a planned total of 36 sessions. This corresponds to an average participation of one session per week. The per-protocol population (Z18 sessions) consisted of 14 participants from the aerobic exercise group with a mean number of attended sessions of 24.1 (SD 4.7) and 13 participants from the control group with a mean number of attended sessions of 22.4 (SD 2.8) (p¼0.10). 3.2. Follow-up Post-intervention, 33/41 (80.5%) in the aerobic exercise group participated in a MRI scan and 22/38 (57.9%) in the control group (p¼ 0.03) suggesting that follow-up was skewed. The pre-intervention right hippocampal volume was 182 mm3 lower (95% CI 0.1–364; p¼0.05), diastolic blood pressure was 5.3 mmHg higher
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Fig. 1. Flow-diagram of participant flow.
3.4. Hippocampal volume
Table 1 Clinical and demographical characteristics. Aerobic exercise N ¼ 41
Exercise control N¼ 38
P value
Age, years Female, n (%) Smoking, daily, n (%)
38.9 (11.7) 30 (73.2) 13 (31.7)
43.8 (12.2) 23 (60.5) 15 (39.5)
0.07 0.34 0.54
Psychometrics HAM-D17 HAM-A14 Generalised anxiety, n (%) Recurrent depression, n (%) Age at first depression
19.0 18.1 23 17 33.9
18.9 16.3 20 20 38.8
(4.6) (6.0) (52.6) (52.6) (13.1)
0.92 0.17 0.82 0.37 0.09
124.3 (17.7)
0.52
80.1 (9.2)
82.6 (13.0)
0.34
76.0 25.8 5.2 26.5
75.6 25.2 5.3 27.2
0.96 0.70 0.72 0.65
Somatic Systolic blood pressure, mmHg Diastolic blood pressure, mmHg Weight, kg (SD) Body mass index (SD) Cholesterol (SD) Maximal oxygen uptake
(3.9) (5.0) (56.1) (41.4) (11.6)
121.8 (15.5)
(22.5) (6.4) (1.1) (7.2)
(17.5) (5.1) (1.4) (5.9)
Mean and standard deviation are reported unless otherwise noted. Abbreviations: HAM-D17—Hamilton Depression Scale, 17 items; HAM-A14—Hamilton Anxiety Scale, 14 items.
(95% CI 0.1–10.7; p¼0.05), and number of attended sessions was on average 10.5 higher (95% CI 7.5–13.5; po0.001) in participants attending the post-intervention MRI compared to non-attenders. Otherwise the attenders and non-attenders to post-intervention MRI were not significantly different on any other reported variable. 3.3. Maximal oxygen uptake Post-intervention the mean maximal oxygen uptake increased with 3.90 ml/kg/min (SD 5.1) in the aerobic exercise group and 0.95 ml/kg/min (SD 6.2) in the control group (p ¼0.03).
Post-intervention, there were no differences in right or left hippocampal volume as illustrated in Fig. 2. Neither did the intervention result in any changes of total hippocampal volume or grey matter volume as displayed in Table 2. Post-hoc we adjusted for age and gender as main effects. This did not change the results. Neither did inclusion of age as an interaction term (age allocation) influence post-intervention hippocampal volumes. 3.5. Neurotrophines and cognitive skills Post-intervention, we found no differences in serum BDNF, VEGF, and IGF-1 levels or any of the assessed cognitive skills between the two groups. 3.6. Per-protocol analysis The per-protocol population (Z18 sessions) consisted of 14 participants from the aerobic exercise group with a mean attendance of 24.1 (SD 4.7) sessions per week and 13 participants from the control group with a mean attendance of 22.4 (SD 2.8) sessions per week (p ¼0.10). Also in this restricted sample we did not find any differences in right hippocampal volume (p ¼0.31), left hippocampal volume (p¼ 0.35), total hippocampal volume (p¼ 0.85), or grey matter volume (p ¼0.37). 3.7. Post-hoc analysis As illustrated in Fig. 3, change in maximal oxygen uptake was not associated to change in total hippocampal volume in this study (p ¼0.85). A positive association was found between an increase in right hippocampal volume and a decrease in HAM-D17 score and an increase in left hippocampal volume and an increase in verbal performance of the Buschke selective reminding test as illustrated
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ITT analysis
cm3 P = 0.91
PP analysis Right Left
Left
Right P = 0.80
P = 0.17
P = 0.50
P = 0.31
P = 0.35
Fig. 2. Right and left hippocampal volumes in response to an exercise intervention. Data are presented as mean (SD). Intention-to-treat analysis (ITT; n¼ 41þ 38) was conducted using multiple imputation adjusting for baseline right hippocampal volume and diastolic blood pressure. Per protocol analysis (PP; n¼ 14þ 13) was conducted and post-intervention data is shown here. Table 2 Hippocampus volume, neurotrophic factors and cognitive skill before and after an exercise intervention. Aerobic exercise N ¼ 41
Brain volumes Total hippocampal, cm3 Right hippocampal Anterior part Left hippocampal Anterior part Grey matter Total brain Neurotrophic factors BDNF, pg/ml VEGF, pg/ml IGF-1, ng/ml Cognitive function DART Buschke, total Rey recall
P valuea Between-group
Exercise control N ¼ 38
Pre-intervention
Post-intervention
Pre-intervention
Post-intervention
Pre
Post
6.353 3.151 1.537 3.202 1.644 624.337 1166.187
6.325 (0.7) 3.117 (0.4) 1.546 (0.3) 3.201 (0.3) 1.605 (0.2) 621.455 (62.0) 1163.100 (108.0)
6.421 3.136 1.599 3.284 1.699 605.591 1167.996
(0.6) (0.4) (0.3) (0.3) (0.2) (101.0) (92.7)
6.380.0 (0.7) 3.110 (0.4) 1.622 (0.3) 3.267 (0.4) 1.651 (0.2) 605.960 (103.0) 1165.000 (96.0)
0.54 0.91 0.43 0.17 0.38 0.32 0.97
0.88 0.80 0.35 0.50 0.50 0.41 0.64
25488.0 (7165) 332.1 (211.3) 88.6 (104)
25043.8 (7428) 312.6 (244.7) 67.4 (110.3)
0.93 0.62 0.94b
0.47 0.86 0.54
– 12.9 (12.3) 23.4 (7.4)
0.79 0.57 0.79
– 0.60 0.28
(0.7) (0.4) (0.3) (0.3) (0.2) (60.8) (108.0)
25347.0 (6224) 309.2 (175.7) 86.6 (110) 34.0 (9.9) 16.4 (12.0) 20.9 (6.7)
26005.5 (7184) 303.8 (182.5) 81.7 (114.6) – 11.4 (10.9) 25.5 (6.4)
34.6 (7.6) 17.9 (11.8) 21.3 (7.2)
Mean and standard deviation are reported. Missing data post-intervention was handled by multiple imputations. a b
P values are based on independent t-test. All comparison of brain volumes are adjusted for whole brain volume. Confirmed in non-parametric analysis.
in Fig. 4. An association between increase in right hippocampal volume and improved performance of the Rey memory test (rho¼ 0.23; p ¼0.10) was borderline significant. No other association between change in maximal oxygen uptake, hippocampal volume, and neurotrophines was observed. At follow-up, 4/33 (12.1%) patients in the aerobic exercise group and 4/22 (18.2%) in the control group had started antidepressant medication (p¼ 0.70). Adjusting for this in the analysis did not change the results.
4. Discussion
Fig. 3. Association between change in total hippocampal volume and change in maximal oxygen uptake. Spearmann's rho and p-value is based on all randomized participants. Missing data post-intervention were handled by multiple imputations.
The primary aim of the current study was to assess hippocampal volume in response to aerobic exercise. We did not find that a three month aerobic exercise intervention increased the hippocampal volume in a group of mild to moderate depressed outpatients. Furthermore, the aerobic exercise intervention did not increase serum levels of BDNF, VEGF or IGF-1. We did, however, find an association between an increase in hippocampal volume, improved depression, and verbal memory independent of exercise.
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Fig. 4. The association between change in right hippocampal volume and HAM-D17 and change in left hippocampal volume and verbal memory. Spearmann's rho and pvalue is based on all randomized participants. Missing data post-intervention were handled by multiple imputations. 1Busckhes Selective Reminding Test.
To our best knowledge, this is the first study to assess hippocampal volume in response to aerobic exercise in patients with major depression. Several randomized clinical trials have previously shown an increase in hippocampal volume in response to aerobic exercise. An increase of 12% was found in a small study of patients with schizophrenia in response to a three month exercise intervention (Pajonk et al., 2010) and an increase of 2% was found in healthy older adults in response to a 6 months exercise programme (Erickson et al., 2011). These findings are supported by non-controlled prospective studies in healthy humans demonstrating an association between increase in hippocampal volume and increase in aerobic fitness (Parker et al., 2011; Pereira et al., 2007). Also, a substantial volume of animal studies support the association between exercise and hippocampal volume (Voss et al., 2013b). However, a recent semi-large randomized clinical trial of patients with schizophrenia was not able to reproduce the previously reported findings in subjects with schizophrenia (Scheewe et al., 2013). Interestingly, the increase in hippocampal volume in trials with positive findings has been linked to increase in maximal oxygen uptake. In the current study the increase in maximal oxygen uptake in the aerobic exercise group was 14.7% compared to 11% in the study by Pajonk et al. (2010) and 7.8% in the study by Erickson et al. (2011) illustrating that increase in maximal oxygen uptake is not sufficient for hippocampal growth and a frequent stimulation of exercise mediated factors on the hippocampus is potentially necessary. Therefore, one potential explanation is the low participation rate in the current study compared to the study by Pajonk et al. (2010) who included 16 patients that participated in 75% of the sessions or more. In our per protocol analysis (n ¼27), including participants that participated in more than 50% of the sessions we did not find any suggestions of hippocampal growth. It is possible that the effect of exercise on hippocampal volume was less than the uncertainty of our measurement and changes of 2% would be smaller than our method would detect. Including patients for this sub-study ended after approaching patient number 90. This was based partly on a rough estimate on expected effect observed in the study by Pajonk et al. (2010), in which exercise programme was very similar to current study, and partly due to the availability and costs of MRI. Assuming a two-sided type 1 error of 5% the current study had a 92% chance (power) of finding a 10% difference post-intervention in left or right hippocampal volume, however, the current setting allow only a 10% chance (power) of finding a 2%
difference post-intervention as observed in the study by Erickson et al. (2011). Therefore, we cannot exclude smaller increases in hippocampal volume in response to an exercise intervention. However, this potential effect on hippocampal volume did not produce clinically relevant results. A neurotrophin like BNDF increases in response to an acute bout of exercise and it is possible that the continuous stimulation of BDNF and other neurotrophines to the brain is responsible for hippocampal growth. To our knowledge, only three randomised clinical trials on exercise and hippocampal growth have been published to date (Erickson et al., 2011; Pajonk et al., 2010;Scheewe et al., 2013) and none of these on patients with depression. Both schizophrenia and increasing age are associated with decreased hippocampal volume. Recent metaanalysis of hippocampal volume in patients with depression suggests that hippocampal volume is reduced only in a subgroup of patients minority of patients (McKinnon et al., 2009) and it could be argued that a pragmatic exercise intervention is unlikely to increase the volume of a non-affected brain structure. The evidence of hippocampal growth in response to exercise in humans is therefore still uncertain and with the current study no data from human subjects supports that exercise in patients with depression will induce hippocampal growth. The increase in hippocampal volume is thought to be mediated partly by neurotrophines such as BDNF, VEGF, and IGF-1. BDNF is responsible for neural survival, growth, and synaptic plasticity and BDNF mRNA is upregulated in the dentate gyrus of the hippocampal region in response to exercise (Vaynman et al., 2004). The current study did not find that aerobic exercise training increases serum levels of BDNF, VEGF, or IGF-1, which is in line with a similar study of healthy older adults (Voss et al., 2013a). In rodents, peripheral blockade of VEGF and IGF-1 has been shown to inhibit the exercise induced hippocampal growth. While BDNF increases in response to acute aerobic exercise, the effect of chronic aerobic exercise training is less clear (Huang et al., 2014). Of particular interest is that Erickson et al. (2011) found that the exercise mediated increase in hippocampal volume was positively associated to increase in BDNF in healthy old participants, which was not confirmed in the present study. Neither did the study by Erickson et al., 2011 find an effect of exercise training on VEGF or IGF-1. IGF-1 should ideally be analysed in the context of the IGF-1 carrier protein IGFB-3, but that analysis was not undertaken in the current study. While it is possible that BDNF in some populations will increase in response to aerobic training there is at present no
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evidence in favour of this in psychiatric populations. Neither is there any support of aerobic exercise training will increase or decrease VEGF or IGF-1 in this patient group. We conducted post-hoc analysis to examine a number of correlations and these results should purely be seen as hypothesis generating. As illustrated, we found an increase in verbal memory performance (Buschke Selective Reminding Test). This association between verbal memory and left hippocampal volume is supported by a previous study finding an association between verbal memory and hippocampal microstructure but these findings were not specifically related to left or right hippocampal region (van Norden et al., 2012). The association between verbal memory performance and left hippocampal volume should also be interpreted in the context of speech production predominantly being situated in the left frontal–temporal region. The association between hippocampal growth and reduction in depressive symptoms supports a role for hippocampus in depression and as previously shown the volume reduction in depression is potentially state dependent and will after recovery (Ahdidan et al., 2011) regain the pre-morbid volume. In summary, an exercise intervention for outpatients with mild to moderate major depression does not increase hippocampal volume and does not increase serum levels of BDNF, VEGF, or IGF-1. Furthermore, we found no association between change in hippocampal volume and change in maximal oxygen uptake Role of the funding source None of the funders had any role in trial design, data collection, manuscript preparation or analysis of data. Jesper Krogh had full access to all of the data in the study and takes full responsibility for the integrity of the data and the accuracy of the data analysis.
Conflict of interests None of the authors report any conflicts of interest. Acknowledgement We thank all the participants, without their interest in our research this study would not have been possible. We are also grateful for the assistance of Eivy Olsen for assessing the participants' cognitive skills and Poul-Henrik Frandsen for assistance with MRI, and Pia Hogh Plougmann for analysis of neutrophines. This study was funded by Trygfonden, Nordea-Danmark fonden, Helsefonden, and Aase and Ejnar Danielsensfond.
References Ahdidan, J., Hviid, L., Chakravarty, M., Ravnkilde, B., Rosenberg, R., Rodell, A., Stodkilde-Jorgensen, H., Videbech, P., 2011. Longitudinal MR study of brain structure and hippocampus volume in major depressive disorder. Acta Psychiatr. Scand. 123 (3), 211–219. Andersen, L.B., 1997. A maximal cycle exercise protocol to predict maximal oxygen uptake. Scand. J. Med. Sci. Sports 5, 143–146. Bech,P., Bech-Andersen,G., Schütze,T., 1999. Mini Internationalt Neuropsykiatrisk Interview. Dansk Version 5.0.0. www. ccmh. dk. Buschke, H., Fuld, P.A., 1974. Evaluating storage, retention, and retrieval in disordered memory and learning. Neurology 24, 1019–1025. Eisch, A.J., Petrik, D., 2012. Depression and hippocampal neurogenesis: a road to remission? Science 338, 72–75. Elfving, B., Plougmann, P., Wegener, G., 2010. Detection of brain-derived neurotrophic factor (BDNF) in rat blood and brain preparations using ELISA: pitfalls and solutions. J. Neurosci. Methods 187, 73–77.
Erickson, K., Voss, M., Prakash, R., Basak, C., Szabo, A., Chaddock, L., Kim, J., Heo, S., Alves, H., White, S., Wojcicki, T, Mailey, E, Vieira, V., Martin, S., Pence, B., Woods, J., McAuley, E, Kramer, A., 2011. Exercise training increases size of hippocampus and improves memory. Proc. Natl. Acad. Sci. USA 108, 3017–3022. FMRIB Software Library. www.fmrib.ox.ac.uk/fsl. Fabel, K., Fabel, K., Tab, B., Kaufer, D., Baiker, A., Simmons, N., Kuo, C., Palmer, T., 2003. VEGF is necessary for exercise-induced adult hippocampal neurogenesis. Eur. J. Neurosci. 18, 2803–2812. Hamilton, M., 1960. A rating scale for depression. J. Neurol. Neurosurg. Psychiatry 23, 56–62. Huang, T., Larsen, K.T., Ried-Larsen, M., Moller, N.C., Andersen, L.B., 2014. The effects of physical activity and exercise on brain-derived neurotrophic factor in healthy humans: a review. Scand. J. Med. Sci. 24 (1), 1–10. Konrad, C., Ukas, T., Nebel, C., Arolt, V., Toga, A.W., Narr, K.L., 2009. Defining the human hippocampus in cerebral magnetic resonance images – an overview of current segmentation protocols. NeuroImage 47, 1185–1195. Krogh, J., Videbech, P., Thomsen, C., Gluud, C., Nordentoft, M., 2012. DEMO-II trial. aerobic exercise versus stretching exercise in patients with major depression – a randomised clinical trial. PLoS One 7 (10), e48316. Malykhin, N.V., Bouchard, T.P., Ogilve, C.J., Coupland, N.J., Seres, P., Camicioli, R., 2007. Three-dimensional volumetric analysis and reconstruction of amygdala, hippocampal head, body and tail. Psychiatr. Res. 155 (2), 155–165. McKinnon, M.C., Yucel, K., Nazarov, A., MacQueen, G.M., 2009. A meta-analysis examining clinical predictors of hippocampal volume in patients with major depressive disorder. J. Psychiatry Neurosci. 34 (1), 41–54. Meyers, J.E., Bayless, J.D., Meyers, K.R., 1996. Rey complex figure: memory error patterns and functional abilities. Appl. Neuropsychol. 3, 89–92. van Norden, A.G., de Laat, K.F., Fick, I., van Uden, I.W., van Oudheusden, L.J., Gons, R.A., Norris, D.G., Zwiers, M.P., Kessels, R.P., de Leeuw, F.E., 2012. Diffusion tensor imaging of the hippocampus and verbal memory performance: the RUN DMC study. Hum. Brain Mapp. 33 (3), 542–551. Pajonk, F., Wobrock, T., Gruber, O., Scherk, H., Berner, D., Kaizl, I., Kierer, A., Muller, S., Oest, M., Meyer, T., Backens, M., Schneider-Axmann, T., Thornton, A., Honer, W., Falkai, P., 2010. Hippocampal plasticity in response to exercise in schizophrenia. Arch. Gen. Psychiatry 67, 133–143. Parker, B.A., Thompson, P.D., Jordan, K.C., Grimaldi, A.S., Assaf, M., Jagannathan, K., Pearlson, G.D., 2011. Effect of exercise training on hippocampal volume in humans: a pilot study. Res. Q. Exerc. Sport 82 (3), 585–591. Pereira, A., Huddleston, D., Brickman, A., Sosunov, S., Hen, R., McKhann, G., Sloan, R., Gage, F., Brown, T., Small, S., 2007. An in vivo correlate of exercise-induced neurogenesis in the adult dentate gyrus. Proc. Natl. Acad. Sci. USA 104, 5638–5643. Scheewe, T.W., van Haren, N.E., Sarkisyan, G., Schnack, H.G., Brouwer, R.M., de, G.M., Hulshoff Pol, H.E., Backx, F.J., Kahn, R.S., Cahn, W., 2013. Exercise therapy, cardiorespiratory fitness and their effect on brain volumes: a randomised controlled trial in patients with schizophrenia and healthy controls. Eur. Neuropsychopharmacol. 23 (7), 675–685. Schumacher, J., Jamra, R., Becker, T., Ohlraun, S., Klopp, N., Binder, E.B., et al., 2005. Evidence for a relationship between genetic variants at the brain-derived neurotrophic factor (BDNF) locus and Major Depression. Biol. Psychiatry 58, 307–314. Shimizu, E., Hashimoto, K., Okamura, N., Koike, K., Komatsu, N., Kumakiri, C., et al., 2003. Alterations of serum levels of brain-derived neurotrophic factor (BDNF) in depressed patients with or without antidepressants. Biol. Psychiatry 54, 70–75. Smith, S.M., Zhang, Y., Jenkinson, M., Chen, J., Mathews, P., Frederico, A., De Stefano, N., 2002. Accurate, robust and automated longitudinal and cross-sectional brain change analysis. NeuroImage 17 (1), 479–489. Tapia-Arancibia, L., Rage, F., Givalois, L., Arancibia, S., 2004. Physiology of BDNF: focus on hypothalamic function. Front. Neuroendocrinol. 25, 77–107. Trejo, J.L., Llorens-Martin, M.V., Torres-Aleman, I., 2008. The effects of exercise on spatial learning and anxiety-like behavior are mediated by an IGF-I-dependent mechanism related to hippocampal neurogenesis. Mol. Cell. Neurosci. 37 (2), 402–411. Vaynman, S., Ying, Z., Gomez-Pinilla, F., 2004. Hippocampal BDNF mediates the efficacy of exercise on synaptic plasticity and cognition. Eur. J. Neurosci. 20, 2580–2590. Videbech, P., Ravnkilde, B., 2004. Hippocampal volume and depression: a metaanalysis of MRI studies. Am. J. Psychiatry 161 (11), 1957–1966. Voss, M.W., Erickson, K.I., Prakash, R.S., Chaddock, L., Kim, J.S., Alves, H., Szabo, A., Phillips, S.M., Wojcicki, T.R., Mailey, E.L., Olson, E.A., Gothe, N., Vieira-Potter, V.J., Martin, S.A., Pence, B.D., Cook, M.D., Woods, J.A., McAuley, E., Kramer, A.F., 2013a. Neurobiological markers of exercise-related brain plasticity in older adults. Brain Behav. Immun. 28, 90–99. Voss, M.W., Vivar, C., Kramer, A.F., van, P.H., 2013b. Bridging animal and human models of exercise-induced brain plasticity. Trends Cogn. Sci. 17 (10), 525–544.
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Journal of Affective Disorders journal homepage: www.elsevier.com/locate/jad
Research report
The effect of exercise on hippocampal volume and neurotrophines in patients with major depression—A randomized clinical trial Jesper Krogh a,n, Egill Rostrup b, Carsten Thomsen c, Betina Elfving d, Poul Videbech e, Merete Nordentoft a a
Mental Health Centre Copenhagen, Mental Health Services in the Capital Region of Denmark, University of Copenhagen, Copenhagen, Denmark Functional Imaging Unit, Department of Diagnostics, Copenhagen University Hospital, Glostrup Hospital, Denmark c Department of Radiology, Rigshospitalet, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark d Translational Neuropsychiatry Unit, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark e Department for Depression and Anxiety Q, Aarhus University Hospital, Risskov, Denmark b
art ic l e i nf o
a b s t r a c t
Article history: Received 4 January 2014 Received in revised form 15 April 2014 Accepted 15 April 2014 Available online 23 April 2014
Background: The hippocampal volume is reduced in patients with major depression. Exercise leads to an increased hippocampal volume in schizophrenia and in healthy old adults. The effect of exercise on hippocampal volume is potentially mediated by brain derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), and insulin like growth factor 1 (IGF-1). The aim of this trial was to assess the effect of an aerobic exercise intervention on hippocampal volume and serum BDNF, VEGF, and IGF-1 in patients with major depression. Methods: Patients were randomized to an aerobic exercise intervention (n ¼ 41) or a control condition (n ¼38). Both interventions consisted of three supervised sessions per week during a three months period. Results: Post-intervention the increase in maximal oxygen uptake was 3.90 ml/kg/min (SD 5.1) in the aerobic exercise group and 0.95 ml/kg/min (SD 6.2) in the control group (p¼0.03). The hippocampal volume, BDNF, VEGF, or IGF-1 did not differ between the two groups. Post-hoc we found a positive association between change in hippocampal volume and verbal memory (Rho ¼0.27; p¼ 0.05) and change in hippocampal volume and depressive symptoms (Rho ¼ 0.30; p¼0.03). Limitations: Participation was low in both groups corresponding to an average participation of one session per week. Conclusion: Despite a significant increase in maximal oxygen uptake, a pragmatic exercise intervention did not increase hippocampal volume or resting levels of neurotrophines in out-patients with mild to moderate major depression. Trial identifier: ClinicalTrials.gov (NCT00695552) & 2014 Elsevier B.V. All rights reserved.
Keywords: Hippocampus Exercise Depression Neurogenesis Memory BDNF
1. Introduction The hippocampal region is thought to play a pivotal role in major depression. This temporal structure is involved in cognitive skills such as memory, learning, regulation of the hypothalamic–pituitary– adrenal (HPA) axis, and mood (Eisch and Petrik, 2012). Meta-analysis suggests that the bilateral hippocampal volume is reduced 0.3–0.4 standard deviations in patients with depression compared to healthy controls (Videbech and Ravnkilde, 2004). It has been speculated that
n Correspondence to: Mental Health Centre Copenhagen, Bispebjerg Bakke 23, Opg. 13a, DK-2400, Denmark. Tel.: þ45 2553 54 85. E-mail address: [email protected] (J. Krogh).
http://dx.doi.org/10.1016/j.jad.2014.04.041 0165-0327/& 2014 Elsevier B.V. All rights reserved.
the observed reduction in hippocampal volume in patients with depression is due to decreased neurogenesis. Randomised clinical trials suggest that exercise leads to an increased hippocampal volume in healthy old adults (Erickson et al., 2011) while the evidence for schizophrenia is conflicting (Pajonk et al., 2010; Scheewe et al., 2013). Furthermore, in two of these trials the increase in hippocampal volume was positively associated to increased maximal oxygen uptake, brain derived neurotrophic factor (BDNF), spatial and verbal memory (Erickson et al. 2011; Pajonk et al., 2010). Studies on rodents have found that the exercise related increase in memory and learning is mediated through an upregulation of BDNF, which has the ability to stimulate synapticplasticity (Tapia-Arancibia et al., 2004). The exercise induced cell
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proliferation is inhibited by peripheral blockade of either insulin growth factor 1 (IGF-1) or vascular endothelial growth factor (VEGF) (Fabel et al., 2003; Trejo et al., 2008), which indicate that the exercise induced neurogenesis is dependent on not only BDNF but peripheral IGF-I and VEGF. Furthermore, it has been shown that antidepressant treatment up-regulates BDNF in humans (Shimizu et al., 2003) and a relationship between genetic variants of BDNF locus and depression has been implied (Schumacher et al., 2005). On this background, it could be argued that low BDNF levels contribute to the pathophysiology of depression, and that exercise has a beneficial effect on mood and cognitive function in patients with depression through an up-regulation of BDNF, VEGF, and IGF-1. The aim of the present study was to determine if a pragmatic exercise intervention compared to an exercise control condition would increase hippocampal volume and increase serum levels of neurotrophines (BDNF, VEGF, and IGF-1) in patients with major depression.
2. Methods 2.1. Design The study was designed as a randomised, parallel-group, superiority trial with blinded outcome assessment. The trial protocol was approved by the local ethics committee (H-A-2008-046), the Danish Data Protection Agency (J.nr. 2008-41-2354), and registered at ClinicalTrials.gov (NCT00695552). Verbal and written informed consent was obtained from all participants involved in the trial.
2.2. Study population All patients were recruited for participation from the DEMO-II trial, a randomized clinical trial evaluating the antidepressant effect of aerobic exercise (Krogh et al., 2012). The initial 90 consecutively enroled participants were asked to participate in the current sub-study. Eligible participants were men and women between 18 and 60 years of age, referred from a clinical setting by a physician or a psychologist, a diagnose of major depression (DSM-IV) based on the Danish version of the Mini International Neuropsychiatric Interview (Bech et al., 1999). The participants all scored above 12 on the HAM-D17 and were able to comprehend the informed consent statement. Exclusion criteria were current drug abuse, any antidepressant medication within the last two months, current psychotherapeutic treatment, contraindications to physical exercise, regular recreational exercise over 1 h per week, suicidal behaviour according to the 17-item Hamilton Depression Rating Scale (HAM-D17, item 3 over 2), pregnancy, or current/previous psychotic or manic symptoms.
2.3. Randomisation Participants were randomized with a 1:1 ratio to either aerobic exercise or an attention control group. Randomisation was stratified according to severity of depression (high or low depression score; high 417 HAM-D17) and blood pressure (high or low blood pressure; high 4 140/95 mmHg). The randomisation was centralised and carried out by the Copenhagen Trial Unit (CTU) using a computerised randomisation sequence with alternating block sizes (alternating 8, 10, and 12) unknown to the investigators. Prior to the first training session the trial physiotherapist did contact the CTU by phone for participant allocation.
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2.4. Blinding Neither participants nor the physiotherapist conducting the intervention were blinded to the allocation. The outcome assessors (the study nurse, the laboratory and the MRI technicians) were all blinded to participant allocation. Prior to the follow-up interview, participants were instructed not to reveal their allocation to the outcome assessors. The statistical analysis and preparation of the first draft was carried out blinded to group assignments. 2.5. Physical examination For the physical examination, the participants were requested to report at the research department between 8:00 and 10:00 a.m. The participants were instructed not to take any food or liquids except for water beginning from midnight prior to the examination and abstain from strenuous physical activity prior to the examination. Height and weight was measured using an electronic weight (Soehnle Medicals, Type 7700, Backnang, Germany). Blood pressure was measured after 5 min of rest in a sitting position. The mean of three consecutive measurements is reported. To estimate the cardiovascular fitness of the participants a bicycle cardiopulmonary exercise test (Ergomedic 839 e, Monark, Vansbro, Sweden) was used based on Andersen's cycle exercise protocol (Andersen, 1997). 2.6. Intervention After baseline assessment the patients were randomised to either aerobic exercise or a control group as described in detail elsewhere(Krogh et al., 2012). In short, both groups were scheduled to participate in 45 min supervised sessions three times per week in a 3 months programme. In the aerobic training group the participants exercised on stationary bikes at approximately 80% of their maximal heart rate, while the training in the exercise control group was predominantly stretching exercises and low impact exercise such as throwing and catching balls. 2.7. Outcomes 2.7.1. Hippocampal volume The primary outcome for this sub-study was the left and right hippocampal volumes measured post-intervention. Hippocampal volume was estimated using magnetic resonance imaging (MRI). MRI volumetric images were acquired on a 3.0T Siemens system using a T1-weighted 3D gradient MPR sequence with a resolution of 1 1 1 mm with the following parameters: TR ¼2250 ms; TE 3 ms; FoV read ¼256 mm; FoV phase ¼100.0%; and flip angle 91. All images were performed in the coronal plane at an angle perpendicular to the hippocampal long axis. All tracings were manually performed by the same rater (JK) who was instructed by a specialist in neuroimaging (ER). After an initial training period the intra-rater reliability was obtained by estimating the left and right hippocampus of the same 10 patients with at least one day between the first and second estimations. The intraclasscorrelation-coefficient of the first and second assessments was 0.98 (95% CI. 0.91–0.99) and 0.95 (95% CI. 0.82–0.99) for the right and left hippocampal regions. In absolute numbers the median difference between first and second assessments was 12.5 mm3 (IQR 121 to 96) and 129 mm3 (IQR 25–178) for right and left hippocampal volumes. Hippocampus was defined as the cornu ammonis, dentate gyrus, and subiculum. Regions of interest were traced in the coronal plane. Sagittal and axial planes were used continuously to assist tracing in the coronal plane. All estimations of volumes were acquired by tracing regions of interest on each coronal image and finally all slices were added in order to determine the volume.
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For tracing and volume estimation an in house programme was used (RIP, written for Matlab). Border definitions were based on common segmentation protocols (Konrad et al., 2009). The anterior border was located in the sagittal plane. Differentiation of amygdala and hippocampus was based on the alveus. The superior border was identified using alveus as an internal landmark, or the temporal horn of the lateral ventricle as an external landmark. The inferior border was defined as the white matter of the parahippocampal gyrus. The inferomedial border was drawn from the tip of white matter from the parahippocampal gyrus medially to cisterna ambiens. The lateral border was defined by CSF of the lateral ventricle as an external landmark. The posterior border was located where an ovoid grey matter appear inferiomedially to the trigone of the lateral ventricle. Head of the hippocampus was anteriorly identified as described above and posteriorly as the last coronal image where the uncal apex was visible (Malykhin et al., 2007). The total volume of the brain tissue and grey matter was estimated with SIENAX (Smith et al., 2002), part of the FSL software package (2013) (FMRIB Software Library). 2.7.2. Neurotrophic factors Previously, we have shown the BDNF levels in plasma samples, but not in serum or whole blood samples, to be affected by the preanalytical conditions (Elfving et al., 2010). BDNF, VEGF, and IGF1 were all estimated using serum samples collected from an antecubital vein after five minutes of rest and stored at 801 until analysis. Quantification of serum BDNF, VEGF, and IGF-1 levels was performed with the enzyme-linked immunosorbent assay (ELISA) kits. The same batch number was used for the entire experiments of BDNF, VEGF, and IGF-1. The standard curves and the samples were run in duplicate, blinded for case and control. Serum BDNF levels were measured using the Quantikine Human BDNF Immunoassay from R&D Systems (USA). The determination was processed according to the manufacturer's specifications and the absorbance was immediately measured at 450 nm with wavelength correction set to 540 nm (EL 800 Universal Microplate reader, Bio-Tek instruments, INC). For the BDNF measurements the samples were diluted 1:20 to be within the range of the standard curve. The standard curves ranged from 62.5 to 2000 pg/ml BDNF. Three internal BDNF controls (high: 1959–3315 pg/ml, medium: 1099– 1525 pg/ml, low: 344–506 pg/ml), commercial available from R&D Systems (USA), were included on each plate. The serum VEGF levels were measured using the Quantikine Human VEGF Immunoassay from R&D Systems (USA). The determination was processed according to the manufacturer's specifications and the absorbance was immediately measured at 450 nm with wavelength correction set to 540 nm (EL 800 Universal Microplate reader, Bio-Tek instruments, INC). The standard curves ranged from 31.2 to 1000 pg/ml VEGF and the samples were run undiluted to be within the range of the standard curve. Three internal VEGF controls (high: 682–1354 pg/ml, medium: 350–686 pg/ml, low: 115–259 pg/ml), commercially available from R&D Systems (USA), were included on each plate. The serum IGF-1 levels were measured using RayBios Human IGF-1 ELISA kit from RayBiotech, Inc (USA). The determination was processed according to the manufacturer's specifications and the absorbance was immediately measured at 450 nm (EL 800 Universal Microplate reader, Bio-Tek instruments, INC). The standard curves ranged from 0.25 to 60 ng/ml IGF-1 and the samples were run undiluted to be within the range of the standard curve. 2.7.3. Assessment of mood and cognitive function Depression severity was assessed using the Hamilton Depression Rating Scale with 17-items (Hamilton, 1960). Assessment of verbal memory was assessed by the Buschke's Selective Reminding test
(Buschke and Fuld, 1974). A list of 10 different unrelated words was read aloud to the participant. The participant is then asked to recall the list. The interviewer repeats the words that the patient misses and the participant is asked to try again until all ten words can be said, or until ten attempts. The score is the total number of blanks or mistakes; thus, a high score indicates poorer performance. Visuospatial memory was assessed by the Rey's Complex Figure Test (Meyers et al., 1996). In this test the participant was shown a geometrically complex figure on a sheet of paper and asked to copy it to another sheet of paper. When this is done the drawings and the original are put away and after three minutes the participant is asked to draw as much of the figure they can recall. The score is calculated based on the tree-minute recall drawing. A high score reflects better performance. 2.8. Statistics The statistical analysis was based on the intention-to-treat principle including all randomised patients regardless of subsequent withdrawal or deviation from the protocol. Assessment of variables measured at baseline and post-intervention was reported using mean and standard deviation. Post-intervention values were compared using student's t-test for unpaired data. Missing values were imputed using the multiple imputation technique available in SPSS, with 100 imputations and 20 iterations having allocation and baseline values as the predicting variables. Per protocol analysis was undertaken including participants who attended Z50% of the scheduled sessions. All significance tests were 2-tailed and p-values r0.05 were considered significant. Statistical analysis was conducted using SPSS version 19.0 (SPSS, Inc.: Chicago, USA).
3. Results The initial 90 patients included in the DEMO-II trial were considered for enrolment in the current sub-study, as displayed in Fig. 1. The inclusion of patients occurred between September 2008 and April 2010. Eleven patients were excluded from MRI due to either severe claustrophobia (n¼10) or metallic implants (n¼1), leaving 79 participants to constitute the current sample. Forty-one were allocated to the aerobic exercise group and 38 were allocated to the control group. The mean age in the included group was 41.3 (SD 12.1) years and consisted of 53/79 (67.1%) female participants. The mean HAM-D17 was 19.0 (SD 4.3), 32/79 (40.5%) had recurrent depression, and 43/79 (54.4%) generalised anxiety disorder comorbid with their depression. The aerobic exercise group and control group were comparable with respect to baseline demographic and clinical characteristics as displayed in Table 1. 3.1. Compliance The mean attendance was 12.9 (SD 9.6) sessions in the aerobic exercise group compared to 12.4 (SD 8.6) sessions in the control group (p¼0.54) of a planned total of 36 sessions. This corresponds to an average participation of one session per week. The per-protocol population (Z18 sessions) consisted of 14 participants from the aerobic exercise group with a mean number of attended sessions of 24.1 (SD 4.7) and 13 participants from the control group with a mean number of attended sessions of 22.4 (SD 2.8) (p¼0.10). 3.2. Follow-up Post-intervention, 33/41 (80.5%) in the aerobic exercise group participated in a MRI scan and 22/38 (57.9%) in the control group (p¼ 0.03) suggesting that follow-up was skewed. The pre-intervention right hippocampal volume was 182 mm3 lower (95% CI 0.1–364; p¼0.05), diastolic blood pressure was 5.3 mmHg higher
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Fig. 1. Flow-diagram of participant flow.
3.4. Hippocampal volume
Table 1 Clinical and demographical characteristics. Aerobic exercise N ¼ 41
Exercise control N¼ 38
P value
Age, years Female, n (%) Smoking, daily, n (%)
38.9 (11.7) 30 (73.2) 13 (31.7)
43.8 (12.2) 23 (60.5) 15 (39.5)
0.07 0.34 0.54
Psychometrics HAM-D17 HAM-A14 Generalised anxiety, n (%) Recurrent depression, n (%) Age at first depression
19.0 18.1 23 17 33.9
18.9 16.3 20 20 38.8
(4.6) (6.0) (52.6) (52.6) (13.1)
0.92 0.17 0.82 0.37 0.09
124.3 (17.7)
0.52
80.1 (9.2)
82.6 (13.0)
0.34
76.0 25.8 5.2 26.5
75.6 25.2 5.3 27.2
0.96 0.70 0.72 0.65
Somatic Systolic blood pressure, mmHg Diastolic blood pressure, mmHg Weight, kg (SD) Body mass index (SD) Cholesterol (SD) Maximal oxygen uptake
(3.9) (5.0) (56.1) (41.4) (11.6)
121.8 (15.5)
(22.5) (6.4) (1.1) (7.2)
(17.5) (5.1) (1.4) (5.9)
Mean and standard deviation are reported unless otherwise noted. Abbreviations: HAM-D17—Hamilton Depression Scale, 17 items; HAM-A14—Hamilton Anxiety Scale, 14 items.
(95% CI 0.1–10.7; p¼0.05), and number of attended sessions was on average 10.5 higher (95% CI 7.5–13.5; po0.001) in participants attending the post-intervention MRI compared to non-attenders. Otherwise the attenders and non-attenders to post-intervention MRI were not significantly different on any other reported variable. 3.3. Maximal oxygen uptake Post-intervention the mean maximal oxygen uptake increased with 3.90 ml/kg/min (SD 5.1) in the aerobic exercise group and 0.95 ml/kg/min (SD 6.2) in the control group (p ¼0.03).
Post-intervention, there were no differences in right or left hippocampal volume as illustrated in Fig. 2. Neither did the intervention result in any changes of total hippocampal volume or grey matter volume as displayed in Table 2. Post-hoc we adjusted for age and gender as main effects. This did not change the results. Neither did inclusion of age as an interaction term (age allocation) influence post-intervention hippocampal volumes. 3.5. Neurotrophines and cognitive skills Post-intervention, we found no differences in serum BDNF, VEGF, and IGF-1 levels or any of the assessed cognitive skills between the two groups. 3.6. Per-protocol analysis The per-protocol population (Z18 sessions) consisted of 14 participants from the aerobic exercise group with a mean attendance of 24.1 (SD 4.7) sessions per week and 13 participants from the control group with a mean attendance of 22.4 (SD 2.8) sessions per week (p ¼0.10). Also in this restricted sample we did not find any differences in right hippocampal volume (p ¼0.31), left hippocampal volume (p¼ 0.35), total hippocampal volume (p¼ 0.85), or grey matter volume (p ¼0.37). 3.7. Post-hoc analysis As illustrated in Fig. 3, change in maximal oxygen uptake was not associated to change in total hippocampal volume in this study (p ¼0.85). A positive association was found between an increase in right hippocampal volume and a decrease in HAM-D17 score and an increase in left hippocampal volume and an increase in verbal performance of the Buschke selective reminding test as illustrated
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ITT analysis
cm3 P = 0.91
PP analysis Right Left
Left
Right P = 0.80
P = 0.17
P = 0.50
P = 0.31
P = 0.35
Fig. 2. Right and left hippocampal volumes in response to an exercise intervention. Data are presented as mean (SD). Intention-to-treat analysis (ITT; n¼ 41þ 38) was conducted using multiple imputation adjusting for baseline right hippocampal volume and diastolic blood pressure. Per protocol analysis (PP; n¼ 14þ 13) was conducted and post-intervention data is shown here. Table 2 Hippocampus volume, neurotrophic factors and cognitive skill before and after an exercise intervention. Aerobic exercise N ¼ 41
Brain volumes Total hippocampal, cm3 Right hippocampal Anterior part Left hippocampal Anterior part Grey matter Total brain Neurotrophic factors BDNF, pg/ml VEGF, pg/ml IGF-1, ng/ml Cognitive function DART Buschke, total Rey recall
P valuea Between-group
Exercise control N ¼ 38
Pre-intervention
Post-intervention
Pre-intervention
Post-intervention
Pre
Post
6.353 3.151 1.537 3.202 1.644 624.337 1166.187
6.325 (0.7) 3.117 (0.4) 1.546 (0.3) 3.201 (0.3) 1.605 (0.2) 621.455 (62.0) 1163.100 (108.0)
6.421 3.136 1.599 3.284 1.699 605.591 1167.996
(0.6) (0.4) (0.3) (0.3) (0.2) (101.0) (92.7)
6.380.0 (0.7) 3.110 (0.4) 1.622 (0.3) 3.267 (0.4) 1.651 (0.2) 605.960 (103.0) 1165.000 (96.0)
0.54 0.91 0.43 0.17 0.38 0.32 0.97
0.88 0.80 0.35 0.50 0.50 0.41 0.64
25488.0 (7165) 332.1 (211.3) 88.6 (104)
25043.8 (7428) 312.6 (244.7) 67.4 (110.3)
0.93 0.62 0.94b
0.47 0.86 0.54
– 12.9 (12.3) 23.4 (7.4)
0.79 0.57 0.79
– 0.60 0.28
(0.7) (0.4) (0.3) (0.3) (0.2) (60.8) (108.0)
25347.0 (6224) 309.2 (175.7) 86.6 (110) 34.0 (9.9) 16.4 (12.0) 20.9 (6.7)
26005.5 (7184) 303.8 (182.5) 81.7 (114.6) – 11.4 (10.9) 25.5 (6.4)
34.6 (7.6) 17.9 (11.8) 21.3 (7.2)
Mean and standard deviation are reported. Missing data post-intervention was handled by multiple imputations. a b
P values are based on independent t-test. All comparison of brain volumes are adjusted for whole brain volume. Confirmed in non-parametric analysis.
in Fig. 4. An association between increase in right hippocampal volume and improved performance of the Rey memory test (rho¼ 0.23; p ¼0.10) was borderline significant. No other association between change in maximal oxygen uptake, hippocampal volume, and neurotrophines was observed. At follow-up, 4/33 (12.1%) patients in the aerobic exercise group and 4/22 (18.2%) in the control group had started antidepressant medication (p¼ 0.70). Adjusting for this in the analysis did not change the results.
4. Discussion
Fig. 3. Association between change in total hippocampal volume and change in maximal oxygen uptake. Spearmann's rho and p-value is based on all randomized participants. Missing data post-intervention were handled by multiple imputations.
The primary aim of the current study was to assess hippocampal volume in response to aerobic exercise. We did not find that a three month aerobic exercise intervention increased the hippocampal volume in a group of mild to moderate depressed outpatients. Furthermore, the aerobic exercise intervention did not increase serum levels of BDNF, VEGF or IGF-1. We did, however, find an association between an increase in hippocampal volume, improved depression, and verbal memory independent of exercise.
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Fig. 4. The association between change in right hippocampal volume and HAM-D17 and change in left hippocampal volume and verbal memory. Spearmann's rho and pvalue is based on all randomized participants. Missing data post-intervention were handled by multiple imputations. 1Busckhes Selective Reminding Test.
To our best knowledge, this is the first study to assess hippocampal volume in response to aerobic exercise in patients with major depression. Several randomized clinical trials have previously shown an increase in hippocampal volume in response to aerobic exercise. An increase of 12% was found in a small study of patients with schizophrenia in response to a three month exercise intervention (Pajonk et al., 2010) and an increase of 2% was found in healthy older adults in response to a 6 months exercise programme (Erickson et al., 2011). These findings are supported by non-controlled prospective studies in healthy humans demonstrating an association between increase in hippocampal volume and increase in aerobic fitness (Parker et al., 2011; Pereira et al., 2007). Also, a substantial volume of animal studies support the association between exercise and hippocampal volume (Voss et al., 2013b). However, a recent semi-large randomized clinical trial of patients with schizophrenia was not able to reproduce the previously reported findings in subjects with schizophrenia (Scheewe et al., 2013). Interestingly, the increase in hippocampal volume in trials with positive findings has been linked to increase in maximal oxygen uptake. In the current study the increase in maximal oxygen uptake in the aerobic exercise group was 14.7% compared to 11% in the study by Pajonk et al. (2010) and 7.8% in the study by Erickson et al. (2011) illustrating that increase in maximal oxygen uptake is not sufficient for hippocampal growth and a frequent stimulation of exercise mediated factors on the hippocampus is potentially necessary. Therefore, one potential explanation is the low participation rate in the current study compared to the study by Pajonk et al. (2010) who included 16 patients that participated in 75% of the sessions or more. In our per protocol analysis (n ¼27), including participants that participated in more than 50% of the sessions we did not find any suggestions of hippocampal growth. It is possible that the effect of exercise on hippocampal volume was less than the uncertainty of our measurement and changes of 2% would be smaller than our method would detect. Including patients for this sub-study ended after approaching patient number 90. This was based partly on a rough estimate on expected effect observed in the study by Pajonk et al. (2010), in which exercise programme was very similar to current study, and partly due to the availability and costs of MRI. Assuming a two-sided type 1 error of 5% the current study had a 92% chance (power) of finding a 10% difference post-intervention in left or right hippocampal volume, however, the current setting allow only a 10% chance (power) of finding a 2%
difference post-intervention as observed in the study by Erickson et al. (2011). Therefore, we cannot exclude smaller increases in hippocampal volume in response to an exercise intervention. However, this potential effect on hippocampal volume did not produce clinically relevant results. A neurotrophin like BNDF increases in response to an acute bout of exercise and it is possible that the continuous stimulation of BDNF and other neurotrophines to the brain is responsible for hippocampal growth. To our knowledge, only three randomised clinical trials on exercise and hippocampal growth have been published to date (Erickson et al., 2011; Pajonk et al., 2010;Scheewe et al., 2013) and none of these on patients with depression. Both schizophrenia and increasing age are associated with decreased hippocampal volume. Recent metaanalysis of hippocampal volume in patients with depression suggests that hippocampal volume is reduced only in a subgroup of patients minority of patients (McKinnon et al., 2009) and it could be argued that a pragmatic exercise intervention is unlikely to increase the volume of a non-affected brain structure. The evidence of hippocampal growth in response to exercise in humans is therefore still uncertain and with the current study no data from human subjects supports that exercise in patients with depression will induce hippocampal growth. The increase in hippocampal volume is thought to be mediated partly by neurotrophines such as BDNF, VEGF, and IGF-1. BDNF is responsible for neural survival, growth, and synaptic plasticity and BDNF mRNA is upregulated in the dentate gyrus of the hippocampal region in response to exercise (Vaynman et al., 2004). The current study did not find that aerobic exercise training increases serum levels of BDNF, VEGF, or IGF-1, which is in line with a similar study of healthy older adults (Voss et al., 2013a). In rodents, peripheral blockade of VEGF and IGF-1 has been shown to inhibit the exercise induced hippocampal growth. While BDNF increases in response to acute aerobic exercise, the effect of chronic aerobic exercise training is less clear (Huang et al., 2014). Of particular interest is that Erickson et al. (2011) found that the exercise mediated increase in hippocampal volume was positively associated to increase in BDNF in healthy old participants, which was not confirmed in the present study. Neither did the study by Erickson et al., 2011 find an effect of exercise training on VEGF or IGF-1. IGF-1 should ideally be analysed in the context of the IGF-1 carrier protein IGFB-3, but that analysis was not undertaken in the current study. While it is possible that BDNF in some populations will increase in response to aerobic training there is at present no
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evidence in favour of this in psychiatric populations. Neither is there any support of aerobic exercise training will increase or decrease VEGF or IGF-1 in this patient group. We conducted post-hoc analysis to examine a number of correlations and these results should purely be seen as hypothesis generating. As illustrated, we found an increase in verbal memory performance (Buschke Selective Reminding Test). This association between verbal memory and left hippocampal volume is supported by a previous study finding an association between verbal memory and hippocampal microstructure but these findings were not specifically related to left or right hippocampal region (van Norden et al., 2012). The association between verbal memory performance and left hippocampal volume should also be interpreted in the context of speech production predominantly being situated in the left frontal–temporal region. The association between hippocampal growth and reduction in depressive symptoms supports a role for hippocampus in depression and as previously shown the volume reduction in depression is potentially state dependent and will after recovery (Ahdidan et al., 2011) regain the pre-morbid volume. In summary, an exercise intervention for outpatients with mild to moderate major depression does not increase hippocampal volume and does not increase serum levels of BDNF, VEGF, or IGF-1. Furthermore, we found no association between change in hippocampal volume and change in maximal oxygen uptake Role of the funding source None of the funders had any role in trial design, data collection, manuscript preparation or analysis of data. Jesper Krogh had full access to all of the data in the study and takes full responsibility for the integrity of the data and the accuracy of the data analysis.
Conflict of interests None of the authors report any conflicts of interest. Acknowledgement We thank all the participants, without their interest in our research this study would not have been possible. We are also grateful for the assistance of Eivy Olsen for assessing the participants' cognitive skills and Poul-Henrik Frandsen for assistance with MRI, and Pia Hogh Plougmann for analysis of neutrophines. This study was funded by Trygfonden, Nordea-Danmark fonden, Helsefonden, and Aase and Ejnar Danielsensfond.
References Ahdidan, J., Hviid, L., Chakravarty, M., Ravnkilde, B., Rosenberg, R., Rodell, A., Stodkilde-Jorgensen, H., Videbech, P., 2011. Longitudinal MR study of brain structure and hippocampus volume in major depressive disorder. Acta Psychiatr. Scand. 123 (3), 211–219. Andersen, L.B., 1997. A maximal cycle exercise protocol to predict maximal oxygen uptake. Scand. J. Med. Sci. Sports 5, 143–146. Bech,P., Bech-Andersen,G., Schütze,T., 1999. Mini Internationalt Neuropsykiatrisk Interview. Dansk Version 5.0.0. www. ccmh. dk. Buschke, H., Fuld, P.A., 1974. Evaluating storage, retention, and retrieval in disordered memory and learning. Neurology 24, 1019–1025. Eisch, A.J., Petrik, D., 2012. Depression and hippocampal neurogenesis: a road to remission? Science 338, 72–75. Elfving, B., Plougmann, P., Wegener, G., 2010. Detection of brain-derived neurotrophic factor (BDNF) in rat blood and brain preparations using ELISA: pitfalls and solutions. J. Neurosci. Methods 187, 73–77.
Erickson, K., Voss, M., Prakash, R., Basak, C., Szabo, A., Chaddock, L., Kim, J., Heo, S., Alves, H., White, S., Wojcicki, T, Mailey, E, Vieira, V., Martin, S., Pence, B., Woods, J., McAuley, E, Kramer, A., 2011. Exercise training increases size of hippocampus and improves memory. Proc. Natl. Acad. Sci. USA 108, 3017–3022. FMRIB Software Library. www.fmrib.ox.ac.uk/fsl. Fabel, K., Fabel, K., Tab, B., Kaufer, D., Baiker, A., Simmons, N., Kuo, C., Palmer, T., 2003. VEGF is necessary for exercise-induced adult hippocampal neurogenesis. Eur. J. Neurosci. 18, 2803–2812. Hamilton, M., 1960. A rating scale for depression. J. Neurol. Neurosurg. Psychiatry 23, 56–62. Huang, T., Larsen, K.T., Ried-Larsen, M., Moller, N.C., Andersen, L.B., 2014. The effects of physical activity and exercise on brain-derived neurotrophic factor in healthy humans: a review. Scand. J. Med. Sci. 24 (1), 1–10. Konrad, C., Ukas, T., Nebel, C., Arolt, V., Toga, A.W., Narr, K.L., 2009. Defining the human hippocampus in cerebral magnetic resonance images – an overview of current segmentation protocols. NeuroImage 47, 1185–1195. Krogh, J., Videbech, P., Thomsen, C., Gluud, C., Nordentoft, M., 2012. DEMO-II trial. aerobic exercise versus stretching exercise in patients with major depression – a randomised clinical trial. PLoS One 7 (10), e48316. Malykhin, N.V., Bouchard, T.P., Ogilve, C.J., Coupland, N.J., Seres, P., Camicioli, R., 2007. Three-dimensional volumetric analysis and reconstruction of amygdala, hippocampal head, body and tail. Psychiatr. Res. 155 (2), 155–165. McKinnon, M.C., Yucel, K., Nazarov, A., MacQueen, G.M., 2009. A meta-analysis examining clinical predictors of hippocampal volume in patients with major depressive disorder. J. Psychiatry Neurosci. 34 (1), 41–54. Meyers, J.E., Bayless, J.D., Meyers, K.R., 1996. Rey complex figure: memory error patterns and functional abilities. Appl. Neuropsychol. 3, 89–92. van Norden, A.G., de Laat, K.F., Fick, I., van Uden, I.W., van Oudheusden, L.J., Gons, R.A., Norris, D.G., Zwiers, M.P., Kessels, R.P., de Leeuw, F.E., 2012. Diffusion tensor imaging of the hippocampus and verbal memory performance: the RUN DMC study. Hum. Brain Mapp. 33 (3), 542–551. Pajonk, F., Wobrock, T., Gruber, O., Scherk, H., Berner, D., Kaizl, I., Kierer, A., Muller, S., Oest, M., Meyer, T., Backens, M., Schneider-Axmann, T., Thornton, A., Honer, W., Falkai, P., 2010. Hippocampal plasticity in response to exercise in schizophrenia. Arch. Gen. Psychiatry 67, 133–143. Parker, B.A., Thompson, P.D., Jordan, K.C., Grimaldi, A.S., Assaf, M., Jagannathan, K., Pearlson, G.D., 2011. Effect of exercise training on hippocampal volume in humans: a pilot study. Res. Q. Exerc. Sport 82 (3), 585–591. Pereira, A., Huddleston, D., Brickman, A., Sosunov, S., Hen, R., McKhann, G., Sloan, R., Gage, F., Brown, T., Small, S., 2007. An in vivo correlate of exercise-induced neurogenesis in the adult dentate gyrus. Proc. Natl. Acad. Sci. USA 104, 5638–5643. Scheewe, T.W., van Haren, N.E., Sarkisyan, G., Schnack, H.G., Brouwer, R.M., de, G.M., Hulshoff Pol, H.E., Backx, F.J., Kahn, R.S., Cahn, W., 2013. Exercise therapy, cardiorespiratory fitness and their effect on brain volumes: a randomised controlled trial in patients with schizophrenia and healthy controls. Eur. Neuropsychopharmacol. 23 (7), 675–685. Schumacher, J., Jamra, R., Becker, T., Ohlraun, S., Klopp, N., Binder, E.B., et al., 2005. Evidence for a relationship between genetic variants at the brain-derived neurotrophic factor (BDNF) locus and Major Depression. Biol. Psychiatry 58, 307–314. Shimizu, E., Hashimoto, K., Okamura, N., Koike, K., Komatsu, N., Kumakiri, C., et al., 2003. Alterations of serum levels of brain-derived neurotrophic factor (BDNF) in depressed patients with or without antidepressants. Biol. Psychiatry 54, 70–75. Smith, S.M., Zhang, Y., Jenkinson, M., Chen, J., Mathews, P., Frederico, A., De Stefano, N., 2002. Accurate, robust and automated longitudinal and cross-sectional brain change analysis. NeuroImage 17 (1), 479–489. Tapia-Arancibia, L., Rage, F., Givalois, L., Arancibia, S., 2004. Physiology of BDNF: focus on hypothalamic function. Front. Neuroendocrinol. 25, 77–107. Trejo, J.L., Llorens-Martin, M.V., Torres-Aleman, I., 2008. The effects of exercise on spatial learning and anxiety-like behavior are mediated by an IGF-I-dependent mechanism related to hippocampal neurogenesis. Mol. Cell. Neurosci. 37 (2), 402–411. Vaynman, S., Ying, Z., Gomez-Pinilla, F., 2004. Hippocampal BDNF mediates the efficacy of exercise on synaptic plasticity and cognition. Eur. J. Neurosci. 20, 2580–2590. Videbech, P., Ravnkilde, B., 2004. Hippocampal volume and depression: a metaanalysis of MRI studies. Am. J. Psychiatry 161 (11), 1957–1966. Voss, M.W., Erickson, K.I., Prakash, R.S., Chaddock, L., Kim, J.S., Alves, H., Szabo, A., Phillips, S.M., Wojcicki, T.R., Mailey, E.L., Olson, E.A., Gothe, N., Vieira-Potter, V.J., Martin, S.A., Pence, B.D., Cook, M.D., Woods, J.A., McAuley, E., Kramer, A.F., 2013a. Neurobiological markers of exercise-related brain plasticity in older adults. Brain Behav. Immun. 28, 90–99. Voss, M.W., Vivar, C., Kramer, A.F., van, P.H., 2013b. Bridging animal and human models of exercise-induced brain plasticity. Trends Cogn. Sci. 17 (10), 525–544.
