- Email: [email protected]
The blockade of presynaptic and postsynaptic bulbospinal inhibition of the cat spinal monosynaptic reflex by imipramine
Brain Research, 110 (1976) 399--402
399
© ElsevierScientificPublishingCompany,Amsterdam- Printed in The Netherlands
The blockade of presynaptic and postsynaptic bulbospinal inhibition of the cat spinal monosynaptic reflex by imipramine
BHAGAVATULA SREE RAMA SASTRY AND JOHN GORDON SINCLAIR Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, B.C. V6T 1 W5 (Canada)
(Accepted March 30th, 1976)
Bulbospinal inhibition of the monosynaptic reflex (MSR) is evoked by a conditioning stimulation in the ventromedial bulbar reticular formationlz. This inhibition involves a postsynaptic inhibition of the MSR (see refs. 9-11). Carpenter et aL 1 found that stimulation in the dorsomedial but not the ventromedial bulbar reticular formation increased the excitability of spinal Ia afferents. On the other hand, Chan and Barnes 3 reported that stimulation in the ventromedial reticular formation did increase the excitability of Ia afferents. Due to the discrepancy in these results it is not clear whether presynaptic inhibition is involved in bulbospinal inhibition of the MSR. Previous findings from our laboratory suggested that a tonically active 5hydroxytryptamine (5-HT) system antagonized bulbospinal inhibition of the MSR (refs. 13 and 14). The present study was conducted to examine whether bulbospinal inhibition of the MSR, evoked by the bulbar stimulation parameters used previouslyl3,14, involves presynaptic and postsynaptic types of inhibition and, if so, to test whether 5-HT systems antagonize both types of inhibition. A mid-collicular decerebration and a spinal laminectomy were performed on 8 cats under temporary ether anesthesia as described in a previous report (Sinclair and Sastry14). The extensor quadriceps (QUAD) nerve was cut peripherally and the ventral roots from L5 to $2 were sectioned at their exit through the dura. The QUADMSR was evoked at 5-see intervals by stimulating the QUAD nerve and recording from the Le ventral root. Bulbospinal inhibition of the MSR was produced by a tlain of square wave pulses (300 msec train, 150 Hz, 0.5 msec pulses) delivered through a concentric bipolar stainless steel electrode positioned in the ventromedial bulbar reticular formation (P 6.7-11.3; L 0-0.5; V --6.2 to --9.4 in the stereotaxic atlas of Snider and NiemerlS). The interval between the end of the train and the stimulus to evoke the MSR was 7.5 msec. The bulbar sites and stimulus intensities were chosen so that the MSR was reduced to about 40 ~ of the control value without producing movement of the facial, neck and the forelimb muscles or disturbing the blood pressure.
400 To determine if bulbospinal inhibition of the MSR revolves both postsynapt~c and presynaptic inhibition we examined the effects of bulbar stimulation on both the antidromic field potential recorded from the QUAD motor nucleus and the excltabrhty of the QUAD Ia afferents as described by Wall 16. The increase in excitablhty of group Ia afferents produced by an appropriate conditioning stimulus is correlated with the negative dorsal tool potential, the depression of the MSR and the depolarization observed by lntrafiber recording of la fibersa.7,8, ~6, and thus is presumed to be the basis for presynaptic inhibition 5. Thus, a tungsten ( < 5 #m exposed tip, about 5 M~2) or a glass microelectrode filled with 3 M NaC1 (about 2 #m, about 3 M£2) was directed towards the QUAD motor nucleus while recording the orthodromic and antidromic field potentials as described by Eccles et al. 6. The tip of the electrode was assumed to be m the QUAD motor nucleus when the magnitudes of the field potentials were maximal. This site was usually 2 mm lateral to the midline and about 4.1 mm below the surface of the spinal cord. The same electrode was also used as a stimulating electrode to antidromically activate the QUAD Ia afferents. It is hkely that only group la afterents are activated by stimulating at th~s depth since group Ib afferents do not extend so far ventrally (Eccles et al.6.7). The resulting compound action potential was recorded from the QUAD peripheral nerve and the magnitude was adjusted to less than 50~,, of its maximal value by decreasing the stimulus intensity. A switch box was used to successively record the unconditioned and bulbar conditioned QUAD-MSR, the antidromic field potential (FP) in the QUAD motor nucleus and the antidromic compound action potential on the QUAD nerve (QUADAP). Four sweeps of each signal were averaged on an Ortec stgnal averager and the resultant &splay was photographed Imipramine HC1 (4 mg/kg i.v.) was then slowly infused over a period of 20 min and its effect on the unconditioned and con&tloned QUAD-MSR, FP and QUADAP was determined after the administration of 2 and 4 mg/kg, lmlpramine had previously been shown to block bulbospinal inhibition of the MSR, very likely by enhancing 5-HT synaptlc transmission due to blocking 5-HT neuronal uptake (see refs. 13 and 14). The 5-HT antagonist, cyproheptadme HCI (5 mg/kg i.v.), was administered 20 min after completing the imipramine injections. During bulbospinal inhibition of the QUAD-MSR the antidromic FP was reduced in s~ze and the QUAD-AP was facilitated (Figs. 1 and 2). These results indicate that bulbospinal inhibition of this extensor MSR involves presynaptic inhibition in addition to postsynaptlc inhibition, which confirms similar observations made by Chan and Barnes 2,3. However, m the majority of experiments a reduction of the field potentml was seen before an enhancement of the QUAD-AP when the bulbar stimulus intensity was gradually increased. Thus, the postsynaptlc type of inhibition would appear to be predominant under these experimental conditions. However, as illustrated by Chan and Barnes 3, the effects of bulbar stimulation on the MSR vary depending on such factors as the pulse frequency, amplitude and train duration. Thus, it is possible that d~fferent stimulation parameters would have altered the ratio of presynaptic to postsynaptJc inhibition. Imipramine antagonized both the reduction of the motoneuronal field potentml
401 MSR 2my
2msec
A
r
FP
i,,
Jlmv
* \~
1reset
v
J
QUAD AP
J O'2 mv 2msec CONTROL
IMI-4
CYP-S
Fig. 1. The blockade of bulbospinal inhibition of the QUAD-MSR (MSR), and the associated reduction in the antidromic motoneuronal field potential (FP) and the facilitation of QUAD-AP by imipramine HCI (IMI, 2 mg/kg i.v. administered twice over 20 min). A reversal of the blockade was produced by cyproheptadine HCI (CYP, 5 mg/kg injected 20 min after the completion of imlpramine administration). The left signals in each pair represent the unconditioned responses and the right signals illustrate the bulbar conditioned responses. Each signal represents the averaged response of 4 sweeps. BSl M$~
OuAo
AP
-50
z
5C
10C
-
2=0
,,.II¢,L JBI.L 0 20
40
610
-2'0
0
20
40
6fO
•••0
JB.L
0
M-~.¢,
20
40
60
TIMEimtn)
Fig. 2. The blockade of bulbospinal inhibition of the QUAD-MSR (BSI-MSR), the associated facihtation of the QUAD-AP and inhibition of the antidromic motoneuronal field potent]al (BSI-FP) by imipramine HC1 (IMI, 2 mg/kg i.v. administered twice). The effects of cyproheptadine HCI (CYP, 5 mg/kg i.v.) are also shown (n = 8). The actual per cent inhibition of the MSR and FP as well as the facilitation of the QUAD-AP was equated to 100% on the final control test in each experiment.
402 a n d the facilitation o f the Q U A D - A P wh~le blocking b u l b o s p i n a l inhibltlon o f the Q U A D - M S R (Figs. 1 a n d 2). In addition, c y p r o h e p t a d i n e partmlly reversed the a b o v e actions o f i m l p r a m m e . A l t h o u g h we have shown t h a t l m i p r a m m e blocks b u l b o spinal i n h i b i h o n o f this M S R t h r o u g h a spmal site o f action 13 we do n o t k n o w ff both the p r e s y n a p t i c a n d p o s t s y n a p t i c c o m p o n e n t s o f the inhib~tlon were blocked at thl~ site. Nevertheless, these results suggest t h a t 5 - H T is involved m a n t a g o m z i n g b o t h the p r e s y n a p t i c a n d postsynapt~c c o m p o n e n t s o f b u l b o s p m a l inhibition o f this extensor MSR. This i n v e s t i g a t i o n was s u p p o r t e d by a g r a n t f r o m the M e d i c a l R e s e a r c h Council o f C a n a d a to J.G.S. a n d a M e d i c a l R e s e a r c h Council S t u d e n t s h i p to B.S.R.S.
1 CARPENTER,D., ENGBERG, I , AND LUNDBERG,A., Primary afferent depolarizahon evoked from brain stem and the cerebellum, Arch. ital. Bwl., 104 (1966) 73-85. 2 CHAN, S. H. H., AND BARNES,C. D., A presynaptic mechanism evoked from brain stem reticular formation m the lumbar cord and its temporal significance, Brain Research, 45 (1972) 101-114. 3 CHAN,S. H. H., AND BARNES,C. D , Postsynaptic effect evoked from brain stem reticular formatmn in lumbar cord and their temporal correlations with a presynaptic mechanism, Arch. ital. Biol., 112 (1974) 81-97. 4 ECCLES,J. C., Presynaphc and postsynaptic inhibitory actions m the spinal cord. In G. MORUZZl, A. FESSARDAND H. H. JASPER (Eds.), Brain Mechanisms, Progr. Brain Res., Vol. 1, Elsevier, Amsterdam, 1963, pp. 1-18. 5 ECCLES,J. C., Presynaptic inhibition in the spinal cord. In J. C. ECCLESAND J. P. SCHAD~(Eds.), Physiology o f Spinal Neurons, Progr. Brain Res., Vol. 12, Elsevier, Amsterdam, 1964, pp. 65-91. 6 ECCLES,J. C., FATT, P., LANDGREN,S., AND WINSBURY,G. J., Spinal cord potentials generated by volleys in the large muscle afferents, J. Physiol. (Lond.), 125 (1954) 590-606. 7 ECCLES, J. C., MAGNI, F., AND WILLIS,W. D., Depolarization of central terminals of group 1 afferent fibres from muscle, J. Physiol. (Lond.), 160 (1962) 62-92 8 ECCLES,J. C., SCHMtDT, F. R., AND WILLIS,W. D., Presynaptic inhibition of the spinal monosynaptlc reflex pathway, J. Physiol. (Lond.), 161 (1962) 282-297. 9 JANKOWSKA,E., LUND, S., LUNDBERG,A., AND POMPEtANO,O., Inhibitory effects evoked through ventral reticulospmal pathways, Arch. ital. Biol., 106 (1968) 124-140. l0 LLINAS,R., ANDTERZUOLO,C. A., Mechanisms of supraspinal actions upon spinal cord activities. Reticular mhibltory mechanisms on alpha-extensor motoneurones, J. Neurophysiol., 27 (1964) 574-591. 11 LLINAS,R., AND TERZUOLO,C A., Mechanisms of supraspinal actions upon spinal cord activities Reticular inhibitory mechanisms upon flexor motoneurones, J. Neurophysiol., 28 (1965) 413-421 12 MAGOUN,H. W., AND RHINES,R., An inhibitory mechanism in the bulbar reticular formation, J Neurophysiol., 9 (1946) 165-171 13 SASTRY,B. S. R., AND StNCLAm, J. G., Serotonm involvement in the blockade of bulbospmal inhibition of the spinal monosynaptic reflex, Brain Research, (1976) in press. 14 SINCLAIR,J. G., AND SASTRY,B. S. R., The blockade of bulbospmal inhibition by imipramine, deslpramine and pargyline, Neuropharmacology, 13 (1974) 643-650. 15 SNtDER, S, AND NIEMER,T. W., A Stereotaxic Atlas of the Cat Brain, 2nd Ed, The University of Chicago Press, Chicago, Ill., 1964. 16 WALL,P. D., Excitability changes in afferent fibre terminations and their relation to slow potentials, J. Physiol. (Lond.), 142 (1958) 1-21.
399
© ElsevierScientificPublishingCompany,Amsterdam- Printed in The Netherlands
The blockade of presynaptic and postsynaptic bulbospinal inhibition of the cat spinal monosynaptic reflex by imipramine
BHAGAVATULA SREE RAMA SASTRY AND JOHN GORDON SINCLAIR Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, B.C. V6T 1 W5 (Canada)
(Accepted March 30th, 1976)
Bulbospinal inhibition of the monosynaptic reflex (MSR) is evoked by a conditioning stimulation in the ventromedial bulbar reticular formationlz. This inhibition involves a postsynaptic inhibition of the MSR (see refs. 9-11). Carpenter et aL 1 found that stimulation in the dorsomedial but not the ventromedial bulbar reticular formation increased the excitability of spinal Ia afferents. On the other hand, Chan and Barnes 3 reported that stimulation in the ventromedial reticular formation did increase the excitability of Ia afferents. Due to the discrepancy in these results it is not clear whether presynaptic inhibition is involved in bulbospinal inhibition of the MSR. Previous findings from our laboratory suggested that a tonically active 5hydroxytryptamine (5-HT) system antagonized bulbospinal inhibition of the MSR (refs. 13 and 14). The present study was conducted to examine whether bulbospinal inhibition of the MSR, evoked by the bulbar stimulation parameters used previouslyl3,14, involves presynaptic and postsynaptic types of inhibition and, if so, to test whether 5-HT systems antagonize both types of inhibition. A mid-collicular decerebration and a spinal laminectomy were performed on 8 cats under temporary ether anesthesia as described in a previous report (Sinclair and Sastry14). The extensor quadriceps (QUAD) nerve was cut peripherally and the ventral roots from L5 to $2 were sectioned at their exit through the dura. The QUADMSR was evoked at 5-see intervals by stimulating the QUAD nerve and recording from the Le ventral root. Bulbospinal inhibition of the MSR was produced by a tlain of square wave pulses (300 msec train, 150 Hz, 0.5 msec pulses) delivered through a concentric bipolar stainless steel electrode positioned in the ventromedial bulbar reticular formation (P 6.7-11.3; L 0-0.5; V --6.2 to --9.4 in the stereotaxic atlas of Snider and NiemerlS). The interval between the end of the train and the stimulus to evoke the MSR was 7.5 msec. The bulbar sites and stimulus intensities were chosen so that the MSR was reduced to about 40 ~ of the control value without producing movement of the facial, neck and the forelimb muscles or disturbing the blood pressure.
400 To determine if bulbospinal inhibition of the MSR revolves both postsynapt~c and presynaptic inhibition we examined the effects of bulbar stimulation on both the antidromic field potential recorded from the QUAD motor nucleus and the excltabrhty of the QUAD Ia afferents as described by Wall 16. The increase in excitablhty of group Ia afferents produced by an appropriate conditioning stimulus is correlated with the negative dorsal tool potential, the depression of the MSR and the depolarization observed by lntrafiber recording of la fibersa.7,8, ~6, and thus is presumed to be the basis for presynaptic inhibition 5. Thus, a tungsten ( < 5 #m exposed tip, about 5 M~2) or a glass microelectrode filled with 3 M NaC1 (about 2 #m, about 3 M£2) was directed towards the QUAD motor nucleus while recording the orthodromic and antidromic field potentials as described by Eccles et al. 6. The tip of the electrode was assumed to be m the QUAD motor nucleus when the magnitudes of the field potentials were maximal. This site was usually 2 mm lateral to the midline and about 4.1 mm below the surface of the spinal cord. The same electrode was also used as a stimulating electrode to antidromically activate the QUAD Ia afferents. It is hkely that only group la afterents are activated by stimulating at th~s depth since group Ib afferents do not extend so far ventrally (Eccles et al.6.7). The resulting compound action potential was recorded from the QUAD peripheral nerve and the magnitude was adjusted to less than 50~,, of its maximal value by decreasing the stimulus intensity. A switch box was used to successively record the unconditioned and bulbar conditioned QUAD-MSR, the antidromic field potential (FP) in the QUAD motor nucleus and the antidromic compound action potential on the QUAD nerve (QUADAP). Four sweeps of each signal were averaged on an Ortec stgnal averager and the resultant &splay was photographed Imipramine HC1 (4 mg/kg i.v.) was then slowly infused over a period of 20 min and its effect on the unconditioned and con&tloned QUAD-MSR, FP and QUADAP was determined after the administration of 2 and 4 mg/kg, lmlpramine had previously been shown to block bulbospinal inhibition of the MSR, very likely by enhancing 5-HT synaptlc transmission due to blocking 5-HT neuronal uptake (see refs. 13 and 14). The 5-HT antagonist, cyproheptadme HCI (5 mg/kg i.v.), was administered 20 min after completing the imipramine injections. During bulbospinal inhibition of the QUAD-MSR the antidromic FP was reduced in s~ze and the QUAD-AP was facilitated (Figs. 1 and 2). These results indicate that bulbospinal inhibition of this extensor MSR involves presynaptic inhibition in addition to postsynaptlc inhibition, which confirms similar observations made by Chan and Barnes 2,3. However, m the majority of experiments a reduction of the field potentml was seen before an enhancement of the QUAD-AP when the bulbar stimulus intensity was gradually increased. Thus, the postsynaptlc type of inhibition would appear to be predominant under these experimental conditions. However, as illustrated by Chan and Barnes 3, the effects of bulbar stimulation on the MSR vary depending on such factors as the pulse frequency, amplitude and train duration. Thus, it is possible that d~fferent stimulation parameters would have altered the ratio of presynaptic to postsynaptJc inhibition. Imipramine antagonized both the reduction of the motoneuronal field potentml
401 MSR 2my
2msec
A
r
FP
i,,
Jlmv
* \~
1reset
v
J
QUAD AP
J O'2 mv 2msec CONTROL
IMI-4
CYP-S
Fig. 1. The blockade of bulbospinal inhibition of the QUAD-MSR (MSR), and the associated reduction in the antidromic motoneuronal field potential (FP) and the facilitation of QUAD-AP by imipramine HCI (IMI, 2 mg/kg i.v. administered twice over 20 min). A reversal of the blockade was produced by cyproheptadine HCI (CYP, 5 mg/kg injected 20 min after the completion of imlpramine administration). The left signals in each pair represent the unconditioned responses and the right signals illustrate the bulbar conditioned responses. Each signal represents the averaged response of 4 sweeps. BSl M$~
OuAo
AP
-50
z
5C
10C
-
2=0
,,.II¢,L JBI.L 0 20
40
610
-2'0
0
20
40
6fO
•••0
JB.L
0
M-~.¢,
20
40
60
TIMEimtn)
Fig. 2. The blockade of bulbospinal inhibition of the QUAD-MSR (BSI-MSR), the associated facihtation of the QUAD-AP and inhibition of the antidromic motoneuronal field potent]al (BSI-FP) by imipramine HC1 (IMI, 2 mg/kg i.v. administered twice). The effects of cyproheptadine HCI (CYP, 5 mg/kg i.v.) are also shown (n = 8). The actual per cent inhibition of the MSR and FP as well as the facilitation of the QUAD-AP was equated to 100% on the final control test in each experiment.
402 a n d the facilitation o f the Q U A D - A P wh~le blocking b u l b o s p i n a l inhibltlon o f the Q U A D - M S R (Figs. 1 a n d 2). In addition, c y p r o h e p t a d i n e partmlly reversed the a b o v e actions o f i m l p r a m m e . A l t h o u g h we have shown t h a t l m i p r a m m e blocks b u l b o spinal i n h i b i h o n o f this M S R t h r o u g h a spmal site o f action 13 we do n o t k n o w ff both the p r e s y n a p t i c a n d p o s t s y n a p t i c c o m p o n e n t s o f the inhib~tlon were blocked at thl~ site. Nevertheless, these results suggest t h a t 5 - H T is involved m a n t a g o m z i n g b o t h the p r e s y n a p t i c a n d postsynapt~c c o m p o n e n t s o f b u l b o s p m a l inhibition o f this extensor MSR. This i n v e s t i g a t i o n was s u p p o r t e d by a g r a n t f r o m the M e d i c a l R e s e a r c h Council o f C a n a d a to J.G.S. a n d a M e d i c a l R e s e a r c h Council S t u d e n t s h i p to B.S.R.S.
1 CARPENTER,D., ENGBERG, I , AND LUNDBERG,A., Primary afferent depolarizahon evoked from brain stem and the cerebellum, Arch. ital. Bwl., 104 (1966) 73-85. 2 CHAN, S. H. H., AND BARNES,C. D., A presynaptic mechanism evoked from brain stem reticular formation m the lumbar cord and its temporal significance, Brain Research, 45 (1972) 101-114. 3 CHAN,S. H. H., AND BARNES,C. D , Postsynaptic effect evoked from brain stem reticular formatmn in lumbar cord and their temporal correlations with a presynaptic mechanism, Arch. ital. Biol., 112 (1974) 81-97. 4 ECCLES,J. C., Presynaphc and postsynaptic inhibitory actions m the spinal cord. In G. MORUZZl, A. FESSARDAND H. H. JASPER (Eds.), Brain Mechanisms, Progr. Brain Res., Vol. 1, Elsevier, Amsterdam, 1963, pp. 1-18. 5 ECCLES,J. C., Presynaptic inhibition in the spinal cord. In J. C. ECCLESAND J. P. SCHAD~(Eds.), Physiology o f Spinal Neurons, Progr. Brain Res., Vol. 12, Elsevier, Amsterdam, 1964, pp. 65-91. 6 ECCLES,J. C., FATT, P., LANDGREN,S., AND WINSBURY,G. J., Spinal cord potentials generated by volleys in the large muscle afferents, J. Physiol. (Lond.), 125 (1954) 590-606. 7 ECCLES, J. C., MAGNI, F., AND WILLIS,W. D., Depolarization of central terminals of group 1 afferent fibres from muscle, J. Physiol. (Lond.), 160 (1962) 62-92 8 ECCLES,J. C., SCHMtDT, F. R., AND WILLIS,W. D., Presynaptic inhibition of the spinal monosynaptlc reflex pathway, J. Physiol. (Lond.), 161 (1962) 282-297. 9 JANKOWSKA,E., LUND, S., LUNDBERG,A., AND POMPEtANO,O., Inhibitory effects evoked through ventral reticulospmal pathways, Arch. ital. Biol., 106 (1968) 124-140. l0 LLINAS,R., ANDTERZUOLO,C. A., Mechanisms of supraspinal actions upon spinal cord activities. Reticular mhibltory mechanisms on alpha-extensor motoneurones, J. Neurophysiol., 27 (1964) 574-591. 11 LLINAS,R., AND TERZUOLO,C A., Mechanisms of supraspinal actions upon spinal cord activities Reticular inhibitory mechanisms upon flexor motoneurones, J. Neurophysiol., 28 (1965) 413-421 12 MAGOUN,H. W., AND RHINES,R., An inhibitory mechanism in the bulbar reticular formation, J Neurophysiol., 9 (1946) 165-171 13 SASTRY,B. S. R., AND StNCLAm, J. G., Serotonm involvement in the blockade of bulbospmal inhibition of the spinal monosynaptic reflex, Brain Research, (1976) in press. 14 SINCLAIR,J. G., AND SASTRY,B. S. R., The blockade of bulbospmal inhibition by imipramine, deslpramine and pargyline, Neuropharmacology, 13 (1974) 643-650. 15 SNtDER, S, AND NIEMER,T. W., A Stereotaxic Atlas of the Cat Brain, 2nd Ed, The University of Chicago Press, Chicago, Ill., 1964. 16 WALL,P. D., Excitability changes in afferent fibre terminations and their relation to slow potentials, J. Physiol. (Lond.), 142 (1958) 1-21.