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Modification of the responses evoked in the cerebellar cortex by limb nerve stimulation during wakefulness and sleep
SHORT COMMUNICATIONS
557
Modification of the responses evoked in the cerebellar cortex by limb nerve stimulation during wakefulness and sleep We have used the technique of recording evoked fields in order to analyse the pathways ending in the cerebellar cortex as mossy (MF) and climbing fibres (CF), during wakefulness and the different stages of sleep. An analysis of the changes of the fields evoked in the cerebellum in these behavioural conditions1, 2 has recently been done. Carli et aL e have found that limb nerve stimulation evokes in the cerebellum an early and a late wave: the former, which has been assumed to be evoked by the monosynaptic excitation of the dorsal spinocerebellar tract (DSCT), does not change during wakefulness and the different stages of sleep; whereas the latter, which has been postulated to be generated by the polysynaptic activation of the DSCT, is reduced in amplitude during desynchronized sleep, and particularly in coincidence with the bursts of rapid eye movements (REMs). It is not known if the evoked potentials were generated by afferents to cerebellar cortex or by corticocerebellar neurones.
%
~V
100
_Ll 1
~ . 200 LL Z
10
1
I
msec
50
CO
z
100
SS
pV 300
DS-REM DS-REN
W
~0
I
2OO ¢--
u_ c)
.
IO0
.
.
.
~ j j j
50
~ fJTJ fJJJ
o
Fig. I. Amplitude of the MF (N3 wave) and CF (CFn: climbing fibre negative wave) fields evoked in a molecular layer of the cerebellar cortex by stimulation of the superficial radial nerve during wakefulness (W), synchronized sleep (SS) and desynchronized sleep (DS-REM). The columns represent the average size of 50 records as obtained by the computer (see specimens in the middle of the figure). The specimen at the top shows the pattern of a single response with the stimuli and the timer. Intensity of stimulating current to superficial radial nerve is 400 t~A (1.25 times threshold). Sweep duration of computer records is 18.5 msec. Brain Research, 18 (t970) 557-559
558
SHORT COMMU NI ('A~TIONS
Experiments were performed on 3 adult cats. Electrodes for monitoring EEG, neck muscle activity and movements of the eyes were implanted under Nembutal anaesthesia (35 mg/kg i.p.). Electrodes similar to those employed by Carli et al."were used to stimulate the superficial radial and the tibial nerves. The threshold intensity of the stimulus was determined by another collar type electrode made with a single wire and placed above the stimulating electrode, Stimulus currents were kept around 1.2-1.6 times threshold in order to excite mainly the larger cutaneous afferents ; 1 or 2 shocks, 0.05-0.1 msec in duration, with a separation of 2.5-3 msec were applied every second. A ring able to carry a small micromanipulator was fixed to the skull in the cerebellar region and evoked fields were recorded by means of glass micropipettes filled with 4 M NaC1 and having a resistance of 1-3 M~}. Single evoked fields were photographed on a moving film and were also fed into an averaging device (Enhancetron 1024 ND800). For recording the evoked fields, the micropipette was positioned in molecular layers: therefore, fields evoked by M F and CF pathways were recorded mainly as negative waves a-5,8 at different latencies 4. The M F evoked wave has been called Na by Eccles e t al. '5 and represents the activity of parallel fibres and Purkinje cells. The CF evoked wave has been labelled by us CF,, (climbing fibre negative wave), and is generated by the activity of Purkinje neurones. In our experiments, the latencies of the Na waves elicited by stimulation of the superficial radial nerve and of the tibial nerve were respectively 5-6 and 7-10 msec. The latencies of the CFn were respectively 10-15 msec and 16-20 msec. The size of each M F and CF evoked field was compared during quiet wakefulness and synchronized sleep, but no significant change was detected, u In contrast,
N3
CFn
i3iFn DS-REM
W
]
pV
[~
500
250
0
N 3 (MF)
CF°
F 1
-'
Fig. 2. Comparison of MF (N3 wave) and CF (CFn: climbing fibre negative waveJ fields evoked in the molecular layer of the cerebellar cortex by stimulation o f the superficial radial nerve during wakefulness (W) and desynchronized sleep (DS-REM). The columns represent the average size of 150 records with the standard deviation (SD). The level of significance of the responsereduction during D S - R E M measured with the t test is ~> 5 %. The specimens are the average of 50 responses obtained by the computer. The episodes are different from those shown in Fig. 1. Sweep duration of specimens is 32.5 msec. Stimulating current is 1.25 times threshold.
Brain Research, 18 (1970) 557-559
SHORT COMMUNICATIONS
559
in all o f the 9 episodes o f d e s y n c h r o n i z e d sleep tested, we have seen a reduction in the a m p l i t u d e o f b o t h waves (Figs. 1 a n d 2). The two waves m a y b e c o m e very small or even be abolished during intense bursts o f rapid eye movements. A c c o r d i n g to Miller and Oscarsson 7 the latency o f o u r Na waves would exclude a t r a n s m i s s i o n t h r o u g h the spinoreticulocerebellar p a t h w a y , whereas the CFn could be m e d i a t e d by all three spino-olivocerebellar p a t h s described by Oscarsson and c o l l a b o r a t o r s (see ref. 7). It has been shown that the fields e v o k e d in the cerebellar cortex, by M F and C F inputs, are r e d u c e d in a m p l i t u d e during deep sleep, and p a r t i c u l a r l y during R E M s . The fields recorded by us are p o s t s y n a p t i c responses o f the cerebellar cortex neurones; the activity o f p r e s y n a p t i c fibres was usually t o o small and has n o t been investigated. F r o m this finding it is possible to conclude that during p a r a d o x i c a l sleep, a n d particularly d u r i n g R E M s , a signal c o m i n g from the p e r i p h e r y does n o t influence the corticocerebellar neurones with the same effectiveness as it does in the other behavioural states and therefore the e l a b o r a t i o n o f external i n f o r m a t i o n is m a r k e d l y altered. It is k n o w n that during R E M s there is an increased firing o f the P u r k i n j e cells 6. Therefore it seems reasonable to p o s t u l a t e that such an altered responsiveness m a y be due, at least in part, to a m e c h a n i s m o f occlusion at cerebellar level, a l t h o u g h changes o f excitability at precerebellar level are likely to occur. Laboratorio di Neurofisiologia del CNR, e lstituto di Fisiologia dell'Universitgt, 56100-Pisa (Italy)
G. F. MARCHESI 1~. MARKEL* P. STRATA
1 BERLUCCHI, G., MUNSON, J. B., AND RIZZOLATTI, G., Changes in click-evoked responses in the auditory system and the cerebellum of free-moving cats during sleep and waking, Arch. ital. Biol., 105 (1967) 118-135. 2 CARLLG., DIETE-SPIFF, K., AND POMPEIANO,O., Cerebellar responses evoked by somatic afferent volleys during sleep and waking, Arch. ital. Biol., 105 (1967) 499 528. 3 ECCLES,J. C., LLIN~.S,R., AND SASAKI,K., The excitatory synaptic action of climbing fibres on the Purkinje cells of the cerebellum, J. Physiol. (Lond.), 182 (1966) 268-296. 4 ECCLES,J. C., PROVIN1, L., STRATA,P., AND T~.BOP,IKOV.A, H., Analysis of electrical potentials evoked in the cerebellar anterior lobe by stimulation of hindlimb and forelimb nerves, Exp. Brain Res., 6 (1968) 171-194. 5 ECCLES,J. C., SASAKr,K., AND STRATA,P., Interpretation of the potential fields generated in the cerebellar cortex by a mossy fibre volley, Exp. Brain Res., 3 (1967) 58-80. 6 MARCUeSl,G. F., AND STRATA, P., Climbing fibers of cat cerebellum: modulation of activity during sleep, Brain Research, 17 (1970) 145-148. 7 MrLLER, S., AND OSCARSSON,O., Termination and functional organization of spino-olivocerebellar paths. In W. S. FIELDS(Ed.), The Cerebellum in Health and Disease, Dallas Neurological Symposium, in press. 8 SASAK~,K., AND STRATA, P., Responses evoked in the cerebellar cortex by stimulating mossy fiber pathways to the cerebellum, Exp. Brain Res., 3 (1967) 95 110. (Accepted January 10th, 1970)
* Present address: Department of Comparative Physiology, E6tv6s Ldrfind University, Budapest VIII. Hungary. Brain Research, 18 (1970) 557-559
557
Modification of the responses evoked in the cerebellar cortex by limb nerve stimulation during wakefulness and sleep We have used the technique of recording evoked fields in order to analyse the pathways ending in the cerebellar cortex as mossy (MF) and climbing fibres (CF), during wakefulness and the different stages of sleep. An analysis of the changes of the fields evoked in the cerebellum in these behavioural conditions1, 2 has recently been done. Carli et aL e have found that limb nerve stimulation evokes in the cerebellum an early and a late wave: the former, which has been assumed to be evoked by the monosynaptic excitation of the dorsal spinocerebellar tract (DSCT), does not change during wakefulness and the different stages of sleep; whereas the latter, which has been postulated to be generated by the polysynaptic activation of the DSCT, is reduced in amplitude during desynchronized sleep, and particularly in coincidence with the bursts of rapid eye movements (REMs). It is not known if the evoked potentials were generated by afferents to cerebellar cortex or by corticocerebellar neurones.
%
~V
100
_Ll 1
~ . 200 LL Z
10
1
I
msec
50
CO
z
100
SS
pV 300
DS-REM DS-REN
W
~0
I
2OO ¢--
u_ c)
.
IO0
.
.
.
~ j j j
50
~ fJTJ fJJJ
o
Fig. I. Amplitude of the MF (N3 wave) and CF (CFn: climbing fibre negative wave) fields evoked in a molecular layer of the cerebellar cortex by stimulation of the superficial radial nerve during wakefulness (W), synchronized sleep (SS) and desynchronized sleep (DS-REM). The columns represent the average size of 50 records as obtained by the computer (see specimens in the middle of the figure). The specimen at the top shows the pattern of a single response with the stimuli and the timer. Intensity of stimulating current to superficial radial nerve is 400 t~A (1.25 times threshold). Sweep duration of computer records is 18.5 msec. Brain Research, 18 (t970) 557-559
558
SHORT COMMU NI ('A~TIONS
Experiments were performed on 3 adult cats. Electrodes for monitoring EEG, neck muscle activity and movements of the eyes were implanted under Nembutal anaesthesia (35 mg/kg i.p.). Electrodes similar to those employed by Carli et al."were used to stimulate the superficial radial and the tibial nerves. The threshold intensity of the stimulus was determined by another collar type electrode made with a single wire and placed above the stimulating electrode, Stimulus currents were kept around 1.2-1.6 times threshold in order to excite mainly the larger cutaneous afferents ; 1 or 2 shocks, 0.05-0.1 msec in duration, with a separation of 2.5-3 msec were applied every second. A ring able to carry a small micromanipulator was fixed to the skull in the cerebellar region and evoked fields were recorded by means of glass micropipettes filled with 4 M NaC1 and having a resistance of 1-3 M~}. Single evoked fields were photographed on a moving film and were also fed into an averaging device (Enhancetron 1024 ND800). For recording the evoked fields, the micropipette was positioned in molecular layers: therefore, fields evoked by M F and CF pathways were recorded mainly as negative waves a-5,8 at different latencies 4. The M F evoked wave has been called Na by Eccles e t al. '5 and represents the activity of parallel fibres and Purkinje cells. The CF evoked wave has been labelled by us CF,, (climbing fibre negative wave), and is generated by the activity of Purkinje neurones. In our experiments, the latencies of the Na waves elicited by stimulation of the superficial radial nerve and of the tibial nerve were respectively 5-6 and 7-10 msec. The latencies of the CFn were respectively 10-15 msec and 16-20 msec. The size of each M F and CF evoked field was compared during quiet wakefulness and synchronized sleep, but no significant change was detected, u In contrast,
N3
CFn
i3iFn DS-REM
W
]
pV
[~
500
250
0
N 3 (MF)
CF°
F 1
-'
Fig. 2. Comparison of MF (N3 wave) and CF (CFn: climbing fibre negative waveJ fields evoked in the molecular layer of the cerebellar cortex by stimulation o f the superficial radial nerve during wakefulness (W) and desynchronized sleep (DS-REM). The columns represent the average size of 150 records with the standard deviation (SD). The level of significance of the responsereduction during D S - R E M measured with the t test is ~> 5 %. The specimens are the average of 50 responses obtained by the computer. The episodes are different from those shown in Fig. 1. Sweep duration of specimens is 32.5 msec. Stimulating current is 1.25 times threshold.
Brain Research, 18 (1970) 557-559
SHORT COMMUNICATIONS
559
in all o f the 9 episodes o f d e s y n c h r o n i z e d sleep tested, we have seen a reduction in the a m p l i t u d e o f b o t h waves (Figs. 1 a n d 2). The two waves m a y b e c o m e very small or even be abolished during intense bursts o f rapid eye movements. A c c o r d i n g to Miller and Oscarsson 7 the latency o f o u r Na waves would exclude a t r a n s m i s s i o n t h r o u g h the spinoreticulocerebellar p a t h w a y , whereas the CFn could be m e d i a t e d by all three spino-olivocerebellar p a t h s described by Oscarsson and c o l l a b o r a t o r s (see ref. 7). It has been shown that the fields e v o k e d in the cerebellar cortex, by M F and C F inputs, are r e d u c e d in a m p l i t u d e during deep sleep, and p a r t i c u l a r l y during R E M s . The fields recorded by us are p o s t s y n a p t i c responses o f the cerebellar cortex neurones; the activity o f p r e s y n a p t i c fibres was usually t o o small and has n o t been investigated. F r o m this finding it is possible to conclude that during p a r a d o x i c a l sleep, a n d particularly d u r i n g R E M s , a signal c o m i n g from the p e r i p h e r y does n o t influence the corticocerebellar neurones with the same effectiveness as it does in the other behavioural states and therefore the e l a b o r a t i o n o f external i n f o r m a t i o n is m a r k e d l y altered. It is k n o w n that during R E M s there is an increased firing o f the P u r k i n j e cells 6. Therefore it seems reasonable to p o s t u l a t e that such an altered responsiveness m a y be due, at least in part, to a m e c h a n i s m o f occlusion at cerebellar level, a l t h o u g h changes o f excitability at precerebellar level are likely to occur. Laboratorio di Neurofisiologia del CNR, e lstituto di Fisiologia dell'Universitgt, 56100-Pisa (Italy)
G. F. MARCHESI 1~. MARKEL* P. STRATA
1 BERLUCCHI, G., MUNSON, J. B., AND RIZZOLATTI, G., Changes in click-evoked responses in the auditory system and the cerebellum of free-moving cats during sleep and waking, Arch. ital. Biol., 105 (1967) 118-135. 2 CARLLG., DIETE-SPIFF, K., AND POMPEIANO,O., Cerebellar responses evoked by somatic afferent volleys during sleep and waking, Arch. ital. Biol., 105 (1967) 499 528. 3 ECCLES,J. C., LLIN~.S,R., AND SASAKI,K., The excitatory synaptic action of climbing fibres on the Purkinje cells of the cerebellum, J. Physiol. (Lond.), 182 (1966) 268-296. 4 ECCLES,J. C., PROVIN1, L., STRATA,P., AND T~.BOP,IKOV.A, H., Analysis of electrical potentials evoked in the cerebellar anterior lobe by stimulation of hindlimb and forelimb nerves, Exp. Brain Res., 6 (1968) 171-194. 5 ECCLES,J. C., SASAKr,K., AND STRATA,P., Interpretation of the potential fields generated in the cerebellar cortex by a mossy fibre volley, Exp. Brain Res., 3 (1967) 58-80. 6 MARCUeSl,G. F., AND STRATA, P., Climbing fibers of cat cerebellum: modulation of activity during sleep, Brain Research, 17 (1970) 145-148. 7 MrLLER, S., AND OSCARSSON,O., Termination and functional organization of spino-olivocerebellar paths. In W. S. FIELDS(Ed.), The Cerebellum in Health and Disease, Dallas Neurological Symposium, in press. 8 SASAK~,K., AND STRATA, P., Responses evoked in the cerebellar cortex by stimulating mossy fiber pathways to the cerebellum, Exp. Brain Res., 3 (1967) 95 110. (Accepted January 10th, 1970)
* Present address: Department of Comparative Physiology, E6tv6s Ldrfind University, Budapest VIII. Hungary. Brain Research, 18 (1970) 557-559