Neuro,~ciem'c L'llers, 136 (1992) 125 128 Elsevier Scientific Publishers Ireland Ltd.
125
NSL 08686
An electrophysiological study of D 2 dopaminergic actions in normal human retina: a tool in Parkinson's disease P a o l o Stanzione, R a i m o n d o T r a v e r s a , M a r i a n g e l a Pierantozzi, R o b e r t a Semprini, M a r i a G r a z i a M a r c i a n i and G i o r g i o B e r n a r d i CTinica Neurologica 11 L,'niver~'it(1di Roma Tot Ver~ata, Rome (ltalv)
(Received 5 February 1992: Revised version received 20 March 1992: Accepted 23 March 1992) Key wor~£:
Retina: Parkinson's disease: Dopamine; Sulpiride; Dopamine De receptor: Pattern electroretinogram: Normal human
A peculiar delicit ofelectrophysiological retinal responses to pattern reversal grating stimuli has been reported in Parkinson's disease [PD) patients. A similar abnormality has been reproduced by means of non-selective dopaminergic antagonists in normal humans. Aim of this study was to verity', by means of a selective De antagonist (sulpiride) administered to normal subjects, whether a D e blockade affects the visual electrophysiological performances with the same trend as observed in PD patients. Pattern electroretinogram (PERG) responses to I cycle per degree (c/d) of spatial frequency at 1 (transient) and 7.5 (steady state) Hz of temporal modulation of a square-wave grating pattern reversal have been recorded in 19 healthy volunteers before and after the administration of 100 mg i.m. of sulpiride. The data are consistent for the following conclusion: a selective D~ antagonist reduces steady state and delays transient retinal responses as expected tk)r a PD mimicking agent.
Several electrophysiological studies have already reported a visual dysfunction in Parkinson's disease (PD). A delay of visual evoked potentials (VEP) was firstly described in ref. 4, and later many studies highlighted a possible retinal origin of the deficit showing pattern electroretinogram (PERG) alteration in PD patients (for a rexiew see ref. 3). Both VEP and P E R G [4, 16] studies described a recovery of the impaired functions after I.DOPA therapy, suggesting that the visual deficit can be related to the involvement of dopaminergic circuits, presumably in the retina [7, 13]. Moreover a modification of the electrophysiological activity of the normal human retina tbllowing the administration of dopaminergic antagonist has been already reported [1,2, 17]. Dopaminergic receptors in the retina have been classified as either D~ or D2 type [7. 10, 13, 15]: however, the role of these two subtypes in the human retina is unknown so far. Unfortunately, none of the electrophysiological studies reported above used drugs with specific D~ or D 2 affinity, which could have provided important insights in the receptorial pathophysiology of PD visual dysfunction. Moreover all these studies did not utilize steady-state stimulation (more than 4 Hz of temporal modulation of the reversal) but only transient stimuli (1 Hz of temporal ('orrespomh, nce. P. Stanzione, Clinica Neurologica I1 Universit'a di Roma, Via O. Raimondo, 00173 Rome, Italy. Fax: (39) (6) 5922086.
modulation) which does not provide a selective response to contrast originating from ganglion cells but a mixed contrast and luminance response originating from 'all the spatial selective elements in the stimulated area' (for a review see ref. 21). Aim of this study was to test the effects of sulpiride, a selective D: antagonist, on the P E R G in normal humans to elucidate whether D: receptor blockade impairs normal human retinal activity and the affected process in the retina. A total of 19 healthy volunteers, ranging between 18 and 40 years of age (mean 25_+8.2 years), were included in the study. They all had normal or corrected-to-normal (20/25 Snellen or better) visual acuity in the tested eyes and gave their informed consent according to the Declaration of Helsinki. Intraocular pressure (by means of a Perkins ophthalmometer) was in the normal range tk~r all the subjects (12.4+0.6 mmHg (S.D.)) and did nol vary more than l mmHg after pharmacological treatment. Vertical square-wave gratings were presented as stimuli on a TV monitor screen at a distance of I 15 cm from the tested eye, subtending 11'55' degrees of visual lield with a spatial frequency (SF) of I cycle per degree (c/d). The mean luminance of the screen was 90 cd/m -~and the contrast between the bars was 97%. Both transient ( 1 Hz of temporal frequency of reversal=2 reversals per second) and steady-state (7.5 Hz of temporal frequency o1" reversal= 15 reversals per second) stimulations were used
126
(Grass Visual Pattern Generator 10VPGB serial 4E21T2). A multichannel system of data analysis (Brain Analyzer) was utilized for recordings. To record PERG signals, a silver-wire electrode (Ote Biomedica ref. no.=99260041133) was positioned in the lower canthus and referred to a EEG cup electrode on the ipsilateral temple [5, 18]. A ground electrode was placed on the forearm. The interelectrode resistance was below 5 KO. Amplifier gain was 200,000x, with bandpass filter set between 1 and 100 Hz (Grass Model 12 Neurodata Acquisition System). Automatic artifact rejection was used. The response analysis time was 500 ms. For the transient response, 100 sweeps were collected twice to ensure repeatability, while for the steady-state signals two trials of 500 traces were averaged and the performance with the best signal-to-noise ratio (calculated as the ratio between the amplitude at 15 Hz divided by the mean amplitude at 14 and 16 Hz) was taken into account. The high number of averaged trials allowed the reduction of the noise components to values near zero, consistently increasing the signal-to-noise ratio (see Fig. 1). Our amplitude values are in agreement with other values previously reported [191. The peak latency of the principal positive transient PERG component (P50) was measured for each experimental condition. The amplitude of P50, measured as the difference between N30 and P50, in the best of the two performances, was taken into account even if its stability is not accepted by all authors [6, 9, 14]. The steady-state signal was analyzed by means of Fast Fourier Transformer analysis (FFT) at the second harmonic frequency
~U
lc/d
~U
2 ~uV ............................ ~ lOOms
TABLE I EFFECT OF SULPtRIDE ON THE RETINAL RESPONSES OBTAINED WITH SQUARE-WAVE GRATING REVERSAL STIMULI OF 1 CYCLE PER DEGREE (c/d) OF SPATIAL FREQUENCY, REVERSED BY 1 Hz AND 7.5 Hz OF TEMPORAL MODULATION Right part: means and standard deviations of amplitude and phase and angular dispersion of PERG responses before and after sulpiride to steady-state stimuli (7.5 Hz of temporal modulation), calculated by means of fast Fourier Transforming (FFT). Note the statistically significant decrease of amplitude. The difference between mean phases was not statistically significant. Left part: mean latency and amplitude (_+standard deviations) values of PERG responses to a transient (1 Hz of temporal modulation) stimuli. Note the statistically significant increase in latency, while the difference between amplitudes is not statistically significant. Sulpiride, 100 mg; spatial frequency 1 c/d. Values are mean _+S.D.
CONTROL
S U L P I R I D E 100 m g
of 15 Hz, utilizing the zero-padding procedure [11] which allowed a resolution of 1 Hz. Phase means and angular dispersion (reported as S.D.) and comparisons between means of the 15 Hz component were accomplished by a Hotelling paired test [20]. Each experimental trial consisted of two recording sessions, performed before and after the drug administration. Nineteen subjects received an i.m. injection of l-sulpiride (100 nag) and were recorded before and 30 min after the administration. The statistical analysis of the differences between latencies and amplitudes was performed by means of the Student t-paired test and controlled by means Wilcoxon matched non-parametric test. Steady state stimulation (7.5 Hz). The mean amplitude and phase values of PERG responses at 1 c/d, before and after sulpiride in 15 subjects, are reported in Table I. Four subjects have not been considered since they had no stable potentials in the control. Sulpiride decreased the amplitude of the PERG responses of 29.8% (+33.8 S.D.). Examples of PERG recordings and FFT, before and after sulpiride injection, are given in Fig. 1 . The statistical analysis, performed by means of Student t-paired test in order to assess the amplitude decrease of the steady-state responses, gave a significance level of P=0.006 (t=-3.20 n=15) of the difference between the responses before and after sulpiride (decrease
Transient (l Hz)
7.5 HZ '"
Steady-state (7.5 Hz)
~ 15 HZ ....
Fig. 1 Steady-state retinal responses (to a grating pattern reversal stimulus of 1 c/d spatial frequency and 7.5 Hz of temporal modulation) of a normal human subject before and after 100 mg i.m. of sulpiride. Left panel: two consecutive averages are superimposed before (upper traces) and after (lower traces) sulpiride administration. Note the repeatability of the steady-state potential in each condition and the reduction of amplitude produced by sulpiride. In the right panel the spectral analyses of the second harmonic (15 Hz) by means of FFT are shown. The values are shown in pV at the analyzed frequency.
Before After
Latency
Amplitude
Amplitude
Phase
(ms)
(,uV)
(uV)
(deg)
0,538_+0.20 0.336_+0:01 *P
125
NSL 08686
An electrophysiological study of D 2 dopaminergic actions in normal human retina: a tool in Parkinson's disease P a o l o Stanzione, R a i m o n d o T r a v e r s a , M a r i a n g e l a Pierantozzi, R o b e r t a Semprini, M a r i a G r a z i a M a r c i a n i and G i o r g i o B e r n a r d i CTinica Neurologica 11 L,'niver~'it(1di Roma Tot Ver~ata, Rome (ltalv)
(Received 5 February 1992: Revised version received 20 March 1992: Accepted 23 March 1992) Key wor~£:
Retina: Parkinson's disease: Dopamine; Sulpiride; Dopamine De receptor: Pattern electroretinogram: Normal human
A peculiar delicit ofelectrophysiological retinal responses to pattern reversal grating stimuli has been reported in Parkinson's disease [PD) patients. A similar abnormality has been reproduced by means of non-selective dopaminergic antagonists in normal humans. Aim of this study was to verity', by means of a selective De antagonist (sulpiride) administered to normal subjects, whether a D e blockade affects the visual electrophysiological performances with the same trend as observed in PD patients. Pattern electroretinogram (PERG) responses to I cycle per degree (c/d) of spatial frequency at 1 (transient) and 7.5 (steady state) Hz of temporal modulation of a square-wave grating pattern reversal have been recorded in 19 healthy volunteers before and after the administration of 100 mg i.m. of sulpiride. The data are consistent for the following conclusion: a selective D~ antagonist reduces steady state and delays transient retinal responses as expected tk)r a PD mimicking agent.
Several electrophysiological studies have already reported a visual dysfunction in Parkinson's disease (PD). A delay of visual evoked potentials (VEP) was firstly described in ref. 4, and later many studies highlighted a possible retinal origin of the deficit showing pattern electroretinogram (PERG) alteration in PD patients (for a rexiew see ref. 3). Both VEP and P E R G [4, 16] studies described a recovery of the impaired functions after I.DOPA therapy, suggesting that the visual deficit can be related to the involvement of dopaminergic circuits, presumably in the retina [7, 13]. Moreover a modification of the electrophysiological activity of the normal human retina tbllowing the administration of dopaminergic antagonist has been already reported [1,2, 17]. Dopaminergic receptors in the retina have been classified as either D~ or D2 type [7. 10, 13, 15]: however, the role of these two subtypes in the human retina is unknown so far. Unfortunately, none of the electrophysiological studies reported above used drugs with specific D~ or D 2 affinity, which could have provided important insights in the receptorial pathophysiology of PD visual dysfunction. Moreover all these studies did not utilize steady-state stimulation (more than 4 Hz of temporal modulation of the reversal) but only transient stimuli (1 Hz of temporal ('orrespomh, nce. P. Stanzione, Clinica Neurologica I1 Universit'a di Roma, Via O. Raimondo, 00173 Rome, Italy. Fax: (39) (6) 5922086.
modulation) which does not provide a selective response to contrast originating from ganglion cells but a mixed contrast and luminance response originating from 'all the spatial selective elements in the stimulated area' (for a review see ref. 21). Aim of this study was to test the effects of sulpiride, a selective D: antagonist, on the P E R G in normal humans to elucidate whether D: receptor blockade impairs normal human retinal activity and the affected process in the retina. A total of 19 healthy volunteers, ranging between 18 and 40 years of age (mean 25_+8.2 years), were included in the study. They all had normal or corrected-to-normal (20/25 Snellen or better) visual acuity in the tested eyes and gave their informed consent according to the Declaration of Helsinki. Intraocular pressure (by means of a Perkins ophthalmometer) was in the normal range tk~r all the subjects (12.4+0.6 mmHg (S.D.)) and did nol vary more than l mmHg after pharmacological treatment. Vertical square-wave gratings were presented as stimuli on a TV monitor screen at a distance of I 15 cm from the tested eye, subtending 11'55' degrees of visual lield with a spatial frequency (SF) of I cycle per degree (c/d). The mean luminance of the screen was 90 cd/m -~and the contrast between the bars was 97%. Both transient ( 1 Hz of temporal frequency of reversal=2 reversals per second) and steady-state (7.5 Hz of temporal frequency o1" reversal= 15 reversals per second) stimulations were used
126
(Grass Visual Pattern Generator 10VPGB serial 4E21T2). A multichannel system of data analysis (Brain Analyzer) was utilized for recordings. To record PERG signals, a silver-wire electrode (Ote Biomedica ref. no.=99260041133) was positioned in the lower canthus and referred to a EEG cup electrode on the ipsilateral temple [5, 18]. A ground electrode was placed on the forearm. The interelectrode resistance was below 5 KO. Amplifier gain was 200,000x, with bandpass filter set between 1 and 100 Hz (Grass Model 12 Neurodata Acquisition System). Automatic artifact rejection was used. The response analysis time was 500 ms. For the transient response, 100 sweeps were collected twice to ensure repeatability, while for the steady-state signals two trials of 500 traces were averaged and the performance with the best signal-to-noise ratio (calculated as the ratio between the amplitude at 15 Hz divided by the mean amplitude at 14 and 16 Hz) was taken into account. The high number of averaged trials allowed the reduction of the noise components to values near zero, consistently increasing the signal-to-noise ratio (see Fig. 1). Our amplitude values are in agreement with other values previously reported [191. The peak latency of the principal positive transient PERG component (P50) was measured for each experimental condition. The amplitude of P50, measured as the difference between N30 and P50, in the best of the two performances, was taken into account even if its stability is not accepted by all authors [6, 9, 14]. The steady-state signal was analyzed by means of Fast Fourier Transformer analysis (FFT) at the second harmonic frequency
~U
lc/d
~U
2 ~uV ............................ ~ lOOms
TABLE I EFFECT OF SULPtRIDE ON THE RETINAL RESPONSES OBTAINED WITH SQUARE-WAVE GRATING REVERSAL STIMULI OF 1 CYCLE PER DEGREE (c/d) OF SPATIAL FREQUENCY, REVERSED BY 1 Hz AND 7.5 Hz OF TEMPORAL MODULATION Right part: means and standard deviations of amplitude and phase and angular dispersion of PERG responses before and after sulpiride to steady-state stimuli (7.5 Hz of temporal modulation), calculated by means of fast Fourier Transforming (FFT). Note the statistically significant decrease of amplitude. The difference between mean phases was not statistically significant. Left part: mean latency and amplitude (_+standard deviations) values of PERG responses to a transient (1 Hz of temporal modulation) stimuli. Note the statistically significant increase in latency, while the difference between amplitudes is not statistically significant. Sulpiride, 100 mg; spatial frequency 1 c/d. Values are mean _+S.D.
CONTROL
S U L P I R I D E 100 m g
of 15 Hz, utilizing the zero-padding procedure [11] which allowed a resolution of 1 Hz. Phase means and angular dispersion (reported as S.D.) and comparisons between means of the 15 Hz component were accomplished by a Hotelling paired test [20]. Each experimental trial consisted of two recording sessions, performed before and after the drug administration. Nineteen subjects received an i.m. injection of l-sulpiride (100 nag) and were recorded before and 30 min after the administration. The statistical analysis of the differences between latencies and amplitudes was performed by means of the Student t-paired test and controlled by means Wilcoxon matched non-parametric test. Steady state stimulation (7.5 Hz). The mean amplitude and phase values of PERG responses at 1 c/d, before and after sulpiride in 15 subjects, are reported in Table I. Four subjects have not been considered since they had no stable potentials in the control. Sulpiride decreased the amplitude of the PERG responses of 29.8% (+33.8 S.D.). Examples of PERG recordings and FFT, before and after sulpiride injection, are given in Fig. 1 . The statistical analysis, performed by means of Student t-paired test in order to assess the amplitude decrease of the steady-state responses, gave a significance level of P=0.006 (t=-3.20 n=15) of the difference between the responses before and after sulpiride (decrease
Transient (l Hz)
7.5 HZ '"
Steady-state (7.5 Hz)
~ 15 HZ ....
Fig. 1 Steady-state retinal responses (to a grating pattern reversal stimulus of 1 c/d spatial frequency and 7.5 Hz of temporal modulation) of a normal human subject before and after 100 mg i.m. of sulpiride. Left panel: two consecutive averages are superimposed before (upper traces) and after (lower traces) sulpiride administration. Note the repeatability of the steady-state potential in each condition and the reduction of amplitude produced by sulpiride. In the right panel the spectral analyses of the second harmonic (15 Hz) by means of FFT are shown. The values are shown in pV at the analyzed frequency.
Before After
Latency
Amplitude
Amplitude
Phase
(ms)
(,uV)
(uV)
(deg)
0,538_+0.20 0.336_+0:01 *P
