The fusimotor activity and natural sleep in the cat The paradoxical phase of sleep in the cat is characterized by silence of the 'tonic' muscular activities and exaggeration of the 'phasic' muscular activities 9. Excitability test of the spinal motoneuron during this sleep in the cat showed an increase of the threshold value for the direct excitation 11. Associated with this, the monosynaptic reflex or recurrent discharge of the motoneuron is depressed4,6,10. It seemed of interest to know how the fusimotor neurons behave during this sleep stage. Recently Gassel and Pompeiano 5 tried to assess the fusimotor activity during the paradoxical sleep in intact cats. They attributed the decrease of the tendon tap response of gastrocnemius muscle to the depressed fusimotor activity. Attempts were made to record single fusimotor unit from the ventral root in the unanesthetized state. Preliminary operations were done under pentobarbital anesthesia. Small brass screws for EEG of cortical somatosensory area and stainless steel electrode for neck E M G were implanted as previously reported 10. The lumbar spinal cord was exposed by laminectomy. Dura was opened and dorsal roots were cut bilaterally from L5 to $2. The left L7 ventral root was also cut at the most distal part. Then the dura as well as the tissues overlying the laminectomized cord were sutured. The following method was used for the recording of single ventral root fibres in an unanesthetized animal. Two thin rod-wires were thrust, respectively, into L4 dorsal spinous process and into rostrodorsal portions of the iliac bones. They were fixed to a specially designed square frame made of light metal. The cat with this frame on its back was able to crawl on the floor, but restrained from reaching the recording site with its forelimbs. Before the observation began, the following procedures were necessary to the cat recovered from the anesthesia. The frame was fixed sufficiendy tightly so that the unit recordings may be possible on the desk. Procaine was injected into lumbar skin and lumbar muscles. Sutured skin, muscles and dura were again opened. After exposing the cord and L7 ventral root, warm liquid paraffin (4-6 ml) was poured. The ventral root L7 was then split into thin fiber strands to be mounted on silver wire electrodes. Fusimotor units were differentiated from large a-motor units by their small size (about 100/~V)I,L They were monopolarly recorded; reference were the killed filaments of the ventral root. Spontaneous activity of the fusimotor fibers was recorded directly on the moving film from the oscilloscope (Tektronix 502 or Nihonkohden VC-6) or indirectly on the ink-writer, simultaneously with EEG record, after passing the pulseshaping circuit. Observation was continued for about 2-6 h. During this period, painful and unpleasant stimuli were carefully avoided and ample care was given to the animal. In this condition the cat fell asleep and showed signs of typical paradoxical phases for 0-6 times. The fusimotor units isolated during the slow wave phase showed a considerable variation of the spontaneous firing rate from 0 to more than 50 impulses/sec. Most of fusimotor units were silent during this phase, compared with the waking state. In units sampled during the slow wave sleep, discharge frequency was compared in slow wave sleep and the succeeding paradoxical sleep phase. Fig. 1 illustrates the discharge pattern of 3 spontaneously firing fusimotor units Brain Research, 3 (1966) 198-201
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F i g 1 Sire altan~ga3ly re=arded single fusimator unit activity and the polygraph, during spontaneous transition from the slow wave sleep (A, B and left part of C ) t o the paradoxical phase of sleep (middle of C ) Polygraphic records are, from top to bottom, E E G from left somato-sensory area (I-SC), posterior cervical mascle activity (NECK), and electro-oculogram ( E Y E ) The 5th trace is the spontaneous activity of a fusimotor unit of L7 ventral r o o t In the 4th trace one spike was picked up from every consecutive 10 spikes from the 5th t r a c e Oscilloscopic traces a h in the lower half of the chart represent samples of the fa~imgtor uait activity In each trace, the upper one includes unit I[ and the lower one unit I and unit I I I Activity of unit I is also shown in the polyg r a p h Spikes are r e t o a c h e d Between A and B, and B and C, polygraphic records were omitted, respectively for 4 min and 30 s e c
recorded during the transition from slow wave to paradoxical sleep. The upper three traces show, respectively, the EEG, nuchal E M G and electro-oculogram. The 5th trace is the fusimotor activity (unit 1). When the spindle bursts appear in the E E G with a certain amount of neck muscle activity and without ocular movements, this unit showed relatively steady firing of 5-10 impulses/sec (A, B, and initial part of C). When, in C, the eyes started to move and the nuchal activity was reduced, the rate of this unit decreased and its steady firing finally stopped. The silent state was interrupted when the animal awakened. At this point (see h, at the right side of chart) the unit resumed activitywhichbecamehigher than that in the control state of slowwave sleep. Oscilloscopic traces in the b o t t o m of Fig. 1 (a to h) show the spike activities of three units which were recorded at corresponding times as indicated in the polygraphic recordings. All these units fired at relatively steady rate during the slow wave sleep. During transitory phase to paradoxical phase, unit II (upper trace) was still firing, though unit I I I (small unit of lower trace) disappeared. Unit I disappeared at a time when the typical paradoxical state developed (d). The trace f illustrates complete silence of these three units. When the eyes moved around excessively (e and g), the spike activities reappeared, and shortest intervals of units I and II in e were significantly shorter than the respective mean firing rate in the slow-wave state. U nit I I I was silent throughout the paradoxical state. When the animal awakened, tonic spontaneous activity reappeared in all units. In total, 23 fusimotor units were recorded during paradoxical sleep phase. Without exception, the spontaneous activity was reduced in rate. In more than half of them, the spike appeared occasionally, often associated with the R E M burst. It is concluded that, while fusimotor neurons during paradoxical sleep differ from other neurons of the central nervous system, such as cells in the visual cortex, lateral geniculate body, sensory motor cortex and brain stem 1-3,8A2, they seem to bear closer resemblance to a-motoneurons. Thus, two influences to the motoneurons could be differentiated from unidentified supraspinal structures : a tonic depressive as well as a phasic facilitatory one. Department of Neurophysiology, Institute of Brain Research, School of Medicine, University of Tokyo, Tokyo (Japan)
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KISOU KUBOTA REISAKU TANAKA
BUCHWALD,J. S., ANDELDRED,E., Activity in muscle-spindle circuits during learning. In D. BARKER (Ed.), Symposium on Muscle Receptors, Hong Kong Univ. Press, 1962, p. 175.' EVARTS,E. V., Activity of neurons in visual cortex of cat during sleep with low voltage and fast EEG activity, J. Neurophysiol., 25 (1962) 812-816. EVARTS,E. V., Temporal patterns of discharge of pyramidal tract neurons during sleep and waking in the monkey, J. Neurophysiol., 27 (1964) 152-171. GASSEL,M. M., MARCmAFAVA,P. L., AND POMPEIANO,O., An analysis of the supraspinal influences acting on motoneurons during sleep in the unrestrained cat. Modification of the recurrent discharge of the alpha motoneurons during sleep, Arch. ital. Biol., 103 (1965) 25-44. GASSEL,M. M., ANDPOMPFaANO,O., Fusimotor~function during sleeffin unrestrained cats. An account of the modulation of the mechanically and electrically evoked monosynaptie reflexes, Arch. ital. Biol., 103 (1965) 347-368.
Brain Research, 3 (1966) 198-201
6 GIAQUINTO,S., POMPEIANO,O., ANDSOMOGYI,I., Supraspinal modulation of heteronymous monosynaptic and polysynaptic reflexes during natural sleep and wakefulness, Arch. ital. Biol., 102 0964) 245-281. 7 HUNT,C. C., The reflex activity of mammalian small nerve fibres, J. Physiol., 115 (1951) 416-469. 8 HUTTENLOCHER,P. R., Evoked and spontaneous activity in single unit of medial brainstem during natural sleep and waking, J. Neurophysiol, 24 (1961) 451-468. 9 JOUVET,M., Reeherches sur les structures nerveuses et lc m6canisme responsables des diff6rentes phases du sommeil physiologique, Arch. ital. Biol., 102 (1962) 125-206. 10 KUBOTA,K., IWAMURA,Y., ANDNIIMI,Y., Monosynaptic reflex and natural sleep in the cat, J. Neurophysiol., 28 (1965) 125-138. ll KUBOTA,K., AND KIDOKORO, Y., Excitability of the membrane of lumbar motor neurons and natural sleep in the cat, Jap. J. Physiol., 16 (1966) 217-226. 12 SAKAKURA,H., ANDIWAMA,K., Unitary recording from cat lateral geniculate during natural sleep. Proc. Jap. Acad., 42 (1966) 418-423. (Received July 21st, 1966) Brain Research, 3 (1966) 198-201
Identification of cerebellar projecting neurones in nucleus reticularis gigantocellularis Investigations using anatomical and electrophysiological techniques have shown that the lateral reticular and paramedian reticular nuclei project to the cerebellum and that nucleus reticularis gigantocellularis (n.r.gc.) projects rostrally and to the spinal cord 1-a,5-12,14,15. The purpose of this note is to present electrophysiological evidence that some neurones in nucleus reticularis gigantocellularis also send axons to the cerebellum. During the course of experiments on the pharmacological properties of brain stem neurones in unanaesthetized decerebrate cats, glass multibarrelled microelectrodes were inserted through the floor of the 4th ventricle as previously described 4. After removal of the cerebellum, bipolar stimulating electrodes were placed in one of the inferior cerebellar peduncles and when single units were encountered tests were made for antidromic activation from these electrodes. Criteria for antidromic excitation were the same as those used in a previous study of reticulospinal neurones 15, i.e. a response of short and constant latency which followed repetitive stimulation and which was cancelled by collision. This collision technique gave evidence that the axons of all the neurones described below were stimulated antidromically, i.e. the antidromic spike was 'cancelled' by a preceding spontaneous or evoked spike. An antidromic spike from one of these units, with a latency of 1.0 msec is shown in Fig. 1. Latencies of other spikes following stimulation of the inferior cerebellar peduncle were between 0.5 and 2.8 msec. All of these responses were from the ipsilateral peduncle and no contralateral projection was found. There were also some 'silent' units which appeared to be antidromically activated but since the collision technique could not be applied to them they have not been included in these results. After removal of the recording electrode from each insertion, surface measurements were made of the electrode placement. Fig. 2 shows a plan of the positions at which cerebellar-projecting neurones were found between 3.5 mm and 6.5 mm Brain Research, 3 (1966) 201-203