Brain Research, 558 (1991) 353-356 © 1991 Elsevier Science Publishers B.V. All fights reserved. 0006-8993/911503.50 ADONIS 0006899391248368
353
BRES 24836
Effects of muscular contraction on discharge patterns of neurons in the medullary raphe nuclei Gary A. Iwamoto 1, Mark E. Clement 2, Richard D. Brtva I and Robert B. McCall 2 1Department of Veterinary Biosciences, University of Illinois, Urbana, IL 61801 (U.S.A.) and 2Division of Cardiovascular Diseases, UpJohn Company, Kalamazoo, MI 49001 (U.S.A.)
(Accepted 11 June 1991) Key words: Raphe nuclei; Muscular contraction; 5-Hydroxytryptamine; Cat
Cells of the medullary raphe nuclei were characterized as sympathoinhibitory (SI), sympathoexcitatory (SE) or serotonergic (5-HT). When muscular contraction (MC) was evoked by stimulation of the L 7 and S1 ventral roots, putative SI cells were inhibited while putative SE cells were excited. 5-HT cells were unaffected by MC. These data are discussed in relation to integration of somatosensory and cardiovascular reflexes. The medullary raphe nuclei (RN) are thought to be involved in many integrative processes. Recent lines of investigation involving the RN have indicated that they play a substantial role in modulating somatosensory 4'5' 13,14 and cardiovascular information 1's-12. Cells of the RN are know n to receive'somatosensory input 14 and an important raphe-spinal projection is thought to be involved with stimulation-produced analgesia (SPA) 4'13'14. The transmission of SPA is thought to be mediated in part by 5-hydroxytryptamine or s e r o t o n i n (5-HT) 4'13'14. In addition, raphe neurons are involved in sympathoexcitatory (SE) and sympathoinhibitory (SI) pathways 1'11' 12. Finally, identified 5-HT neurons 2'it provide a tonic excitatory input to sympathetic preganglionic cells 9'11, but are not correlated with the 2-6 Hz rhythm of sympathetic nerve discharge (SND) 11. SE, SI and 5-HT neurons thus represent 3 distinct cardiovascular neuronal types in the medullary R N 11. It is also known that the pressor response to muscular contraction which is mediated by Group III and Group IV small diameter afferents has a vital supraspinal component 7. While the ventrolateral medulla is known to participate as an integrative site in this response 7, it is not clear if the RN have any role in this process. This possibility exists since the midline medulla modulates both somatosensory and cardiovascular information. Therefore, the present study was designed to determine if individual raphe neurons could serve to integrate both somatosensory and cardiovascular information.
Anesthesia was induced in adult cats using ketamine hydrochloride (11 mg/kg, i.m.). Blood pressure was monitored through one common carotid artery. Anesthesia was continued with alpha chloralose (80 mg/kg i.v.) (5 cats) or Dial/urethane (60 mg/kg; 240 mg/kg) (2 cats). A lumbar laminectomy exposed the L 7 and S: ventral roots which were mounted on hook-stimulating electrodes. Exposed neural tissue was covered with mineral oil. The triceps surae muscle group was isolated at the calcaneal tendon to measure muscle tension. Stimulation of the cut ventral roots (0.1 ms monophasic pulses, 30-40 Hz, 3x motor threshold) evoked muscular contraction (MC) which in turn evoked pressor reflexes. The baroreceptor (BARO) reflex was induced by the inflation of a Fogarty embolectomy balloon catheter in the abdominal aorta at the level of the diaphragm introduced through a femoral artery. Peripheral sympathetic activity was recorded from the central end of the sectioned left postganglionic inferior cardiac nerve. Potentials were recorded monophasically under mineral oil with a bipolar platinum hook electrode. A bandpass of 1-1000 Hz was used to display the synchronized discharges of the whole sympathetic nerve in the form of slow waves. Activity of cells was monitored with either 4-MQ tungsten microelectrodes or 5-barrel micropipettes inserted at the midline in a zone which included the rostral end of raphe obscurus and raphe pallidus and the caudal pole of the raphe magnus.
Correspondence: G.A. Iwamoto, Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, Urbana, IL 61801, U.S.A.
354 The 5-barrel micropipettes were also used to apply 5-HT iontophoretically] 1. Inferior cardiac SND, unitary cell discharges, blood pressure and pulses derived from the R-wave of the electrocardiogram were recorded on magnetic tape. The signals were analyzed with an RC Electronics Computerscope system (IBM AT computer-based): the unit discharges (conditioned by a window discriminator) were used to trigger averages of the SND (spike-triggered averaging 1L12. A random pulse generator was used in place of the unit discharge to trigger 'dummy' averages for comparison purposes. The R-wave was used to trigger compilation of a histogram of the unit discharges. SI, and SE cells were identified in the RN (Fig. 1) by previously established criteria 3'11'12. Fig. 1 (left) shows a cell which exhibited an irregular discharge but was temporally correlated with the slow wave sympathetic nerve
A1
A2
B1 ~6Osec~
lllrli ..... i ...........
Muscle Tension (Kg)
activity (SND) in the inferior cardiac nerve (Fig. IC1). This cell was also excited during an elevation of arterial blood pressure induced by inflating the Fogarty embolectomy catheter (Fig. 1A1). These characteristics are consistent with the neuron mediating a sympathoinhibitory function (i.e. SI neuron). The cell was inhibited during MC (Fig. 1B1). Of the I I SI cells, all were inhibited during MC. Fig. 1 (right) also shows a cell which was inhibited during the stimulation of the baroreflex (Fig. 1A2) and showed a temporal correlation with SND (Fig. 1C2). These characteristics are consistent with a sympathoexcitatory function (i.e. SE neuron). This cell was excited during muscular contraction (Fig. 1B2). We recorded from 8 of these cells of which 6 were excited during MC. The remaining SE cells were inhibited. 5-HT cells in the midline medulla were also identified
i ........
ill ...... ; .........
ill .........
'~
60 sec
B2
lilllliflJl
2,
4 [oL
200 :
Pressure
V
lOO
(mmHg) 50 ~
~v~;
loo ~v
Disoh.
Ill ji
Number of Impulses
C2
C1
L
I
I
t
I
I I I I I J Scale: 200,0 mseC/dlv.
L I l l l
L
I
I
I
I
I P I I I I Scakl: 200.0 msee-Jdh',
Fig. 1. Response of a putative sympathoinhibitory cell (left side) and a putative sympathoexcitatory cell (right side) in the raphe nuclei to muscular contraction. The SI cell was (B1) inhibited during muscular contraction. This cell was (AI) excited during baroreceptor stimulation
with a Fogarty embolectomy catheter. Finally, the cell showed a temporal correlation (C1 left) with SND on basis of the spike-triggered (1183 discharges) midsignal average compared to a dummy average (C1 right). Vertical lines in C1 right and left indicate the time the cell fires or dummy pulse appears. The SE cell was inhibited (A2) during baroreceptor stimulation but was excited (B2) during muscular contraction. This cell also showed a temporal correlation (C2 left) with SND (873 events) compared with the dummy average (C2 right).
355
A
Tension
(Kg)
o
Blood
15o
(mmHg)
too
B
,1
353
BRES 24836
Effects of muscular contraction on discharge patterns of neurons in the medullary raphe nuclei Gary A. Iwamoto 1, Mark E. Clement 2, Richard D. Brtva I and Robert B. McCall 2 1Department of Veterinary Biosciences, University of Illinois, Urbana, IL 61801 (U.S.A.) and 2Division of Cardiovascular Diseases, UpJohn Company, Kalamazoo, MI 49001 (U.S.A.)
(Accepted 11 June 1991) Key words: Raphe nuclei; Muscular contraction; 5-Hydroxytryptamine; Cat
Cells of the medullary raphe nuclei were characterized as sympathoinhibitory (SI), sympathoexcitatory (SE) or serotonergic (5-HT). When muscular contraction (MC) was evoked by stimulation of the L 7 and S1 ventral roots, putative SI cells were inhibited while putative SE cells were excited. 5-HT cells were unaffected by MC. These data are discussed in relation to integration of somatosensory and cardiovascular reflexes. The medullary raphe nuclei (RN) are thought to be involved in many integrative processes. Recent lines of investigation involving the RN have indicated that they play a substantial role in modulating somatosensory 4'5' 13,14 and cardiovascular information 1's-12. Cells of the RN are know n to receive'somatosensory input 14 and an important raphe-spinal projection is thought to be involved with stimulation-produced analgesia (SPA) 4'13'14. The transmission of SPA is thought to be mediated in part by 5-hydroxytryptamine or s e r o t o n i n (5-HT) 4'13'14. In addition, raphe neurons are involved in sympathoexcitatory (SE) and sympathoinhibitory (SI) pathways 1'11' 12. Finally, identified 5-HT neurons 2'it provide a tonic excitatory input to sympathetic preganglionic cells 9'11, but are not correlated with the 2-6 Hz rhythm of sympathetic nerve discharge (SND) 11. SE, SI and 5-HT neurons thus represent 3 distinct cardiovascular neuronal types in the medullary R N 11. It is also known that the pressor response to muscular contraction which is mediated by Group III and Group IV small diameter afferents has a vital supraspinal component 7. While the ventrolateral medulla is known to participate as an integrative site in this response 7, it is not clear if the RN have any role in this process. This possibility exists since the midline medulla modulates both somatosensory and cardiovascular information. Therefore, the present study was designed to determine if individual raphe neurons could serve to integrate both somatosensory and cardiovascular information.
Anesthesia was induced in adult cats using ketamine hydrochloride (11 mg/kg, i.m.). Blood pressure was monitored through one common carotid artery. Anesthesia was continued with alpha chloralose (80 mg/kg i.v.) (5 cats) or Dial/urethane (60 mg/kg; 240 mg/kg) (2 cats). A lumbar laminectomy exposed the L 7 and S: ventral roots which were mounted on hook-stimulating electrodes. Exposed neural tissue was covered with mineral oil. The triceps surae muscle group was isolated at the calcaneal tendon to measure muscle tension. Stimulation of the cut ventral roots (0.1 ms monophasic pulses, 30-40 Hz, 3x motor threshold) evoked muscular contraction (MC) which in turn evoked pressor reflexes. The baroreceptor (BARO) reflex was induced by the inflation of a Fogarty embolectomy balloon catheter in the abdominal aorta at the level of the diaphragm introduced through a femoral artery. Peripheral sympathetic activity was recorded from the central end of the sectioned left postganglionic inferior cardiac nerve. Potentials were recorded monophasically under mineral oil with a bipolar platinum hook electrode. A bandpass of 1-1000 Hz was used to display the synchronized discharges of the whole sympathetic nerve in the form of slow waves. Activity of cells was monitored with either 4-MQ tungsten microelectrodes or 5-barrel micropipettes inserted at the midline in a zone which included the rostral end of raphe obscurus and raphe pallidus and the caudal pole of the raphe magnus.
Correspondence: G.A. Iwamoto, Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, Urbana, IL 61801, U.S.A.
354 The 5-barrel micropipettes were also used to apply 5-HT iontophoretically] 1. Inferior cardiac SND, unitary cell discharges, blood pressure and pulses derived from the R-wave of the electrocardiogram were recorded on magnetic tape. The signals were analyzed with an RC Electronics Computerscope system (IBM AT computer-based): the unit discharges (conditioned by a window discriminator) were used to trigger averages of the SND (spike-triggered averaging 1L12. A random pulse generator was used in place of the unit discharge to trigger 'dummy' averages for comparison purposes. The R-wave was used to trigger compilation of a histogram of the unit discharges. SI, and SE cells were identified in the RN (Fig. 1) by previously established criteria 3'11'12. Fig. 1 (left) shows a cell which exhibited an irregular discharge but was temporally correlated with the slow wave sympathetic nerve
A1
A2
B1 ~6Osec~
lllrli ..... i ...........
Muscle Tension (Kg)
activity (SND) in the inferior cardiac nerve (Fig. IC1). This cell was also excited during an elevation of arterial blood pressure induced by inflating the Fogarty embolectomy catheter (Fig. 1A1). These characteristics are consistent with the neuron mediating a sympathoinhibitory function (i.e. SI neuron). The cell was inhibited during MC (Fig. 1B1). Of the I I SI cells, all were inhibited during MC. Fig. 1 (right) also shows a cell which was inhibited during the stimulation of the baroreflex (Fig. 1A2) and showed a temporal correlation with SND (Fig. 1C2). These characteristics are consistent with a sympathoexcitatory function (i.e. SE neuron). This cell was excited during muscular contraction (Fig. 1B2). We recorded from 8 of these cells of which 6 were excited during MC. The remaining SE cells were inhibited. 5-HT cells in the midline medulla were also identified
i ........
ill ...... ; .........
ill .........
'~
60 sec
B2
lilllliflJl
2,
4 [oL
200 :
Pressure
V
lOO
(mmHg) 50 ~
~v~;
loo ~v
Disoh.
Ill ji
Number of Impulses
C2
C1
L
I
I
t
I
I I I I I J Scale: 200,0 mseC/dlv.
L I l l l
L
I
I
I
I
I P I I I I Scakl: 200.0 msee-Jdh',
Fig. 1. Response of a putative sympathoinhibitory cell (left side) and a putative sympathoexcitatory cell (right side) in the raphe nuclei to muscular contraction. The SI cell was (B1) inhibited during muscular contraction. This cell was (AI) excited during baroreceptor stimulation
with a Fogarty embolectomy catheter. Finally, the cell showed a temporal correlation (C1 left) with SND on basis of the spike-triggered (1183 discharges) midsignal average compared to a dummy average (C1 right). Vertical lines in C1 right and left indicate the time the cell fires or dummy pulse appears. The SE cell was inhibited (A2) during baroreceptor stimulation but was excited (B2) during muscular contraction. This cell also showed a temporal correlation (C2 left) with SND (873 events) compared with the dummy average (C2 right).
355
A
Tension
(Kg)
o
Blood
15o
(mmHg)
too
B
,1
