Reticulofugal influences of interneurons in the lateral region of gray matter of the cat spinal cord

Responses of lumbar interneurons located in the most lateral regions of Rexed's laminae IV–VII to stimulation of the medial longitudinal bundle and gigantocellular reticular nucleus of medullary pyramids, red nucleus, and peripheral nerves were investigated in cats anesthetized with pentobarbital. Stimulation of the reticulospinal fibers evoked monosynaptic excitation of many interneurons specialized for transmitting activity of the lateral descending systems, but not of peripheral afferents. Convergence of excitatory influences of all three descending systems (cortico-, rubro-, and reticulospinal) was observed on some cells of this group. In addition, monosynaptic "reticular" E PSPs appeared in interneurons transmitting activity of group Ia muscle fibers and in some interneurons of the flexor reflex afferent system. Stimulation of reticulospinal fibers evoked IPSPs in some neurons of this last group. Neurons not exposed to reticulofugal influences (both specialized neurons and interneurons of segmental reflex arcs) were located chiefly in the dorsal zones of the region studied. Recordings were also obtained from single fibers of the lateral reticulospinal tracts (conduction velocity from 26 to 81 m/sec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 525–536, September–October, 1973.     

Cortico- and rubrofugal activation of interneurons forming the propriospinal pathways of the dorsolateral funiculus of the cat spinal cord

Interneurons of the lumbar division of the cat spinal cord responding after a short latent period with intensive excitation to stimulation of the medullary pyramids and red nucleus but not responding (or excited after a long latent period) to stimulation of peripheral nerves were investigated by microelectrode recording. Most of these neurons, located in the lateral zones of Rexed's laminae IV–VII of the gray matter, were identified as propriospinal cells sending axons into the dorsolateral funiculus of the white matter (mean velocity of antidromic conduction in the group 34.6 m/sec). Marked convergence of corticofugal and rubrofugal excitatory influences was found on the overwhelming majority of neurons. Some neurons were activated monosynaptically by fast-conducting fibers of both descending systems. The minimal and mean values of the latent periods of the pyramidal EPSPs for the neurons tested were 4.5 and 6.28 msec, and for the rubral EPSPs 3.3 and 4.94 msec respectively. A distinguishing feature of the activation of these neurons is the intensive potentiation of their synaptic action on the arrival of a series of corticofugal and rubrofugal waves.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 489–500, September–October, 1972.     

Transmission of descending activity evoked by prolonged stimulation of the pyramids and red nucleus by groups of spinal interneurons

Responses of two groups of spinal interneurons to prolonged stimulation of the medullary pyramids and the red nucleus by repetitive and random sequences of stimuli were investigated in cats anesthetized with pentobarbital. Interneurons specialized for transmission of descending, but not peripheral, effects were excited by impulses from both higher structures; the evoked activity was stable and stationary in character in response to stimulation within the range from 20–30 to 75–100/sec. The response of interneurons activated by flexor reflex afferents was more complex and, as a rule, it was not stationary. Prolonged pyramidal stimulation led to an increase in the mean spontaneous firing rate, while stimulation of the red nucleus inhibited spontaneous activity. Statistical analysis of the records of unit activity on the "Dnepr'-1" computer was used to study some possible mechanisms of the transformation of activity in the lateral descending systems by these groups of interneurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 644–653, November–December, 1973.     

Synaptic connections of fibers of the rubrospinal tract in the cat spinal cord

The ultrastructure of the lateral part of laminae VI and VII of the spinal gray matter (the location of most of the terminal branches of the rubrospinal tract) was investigated in cats under normal conditions and at various times after destruction of the red nucleus. The neuron population of this region is formed by cells fairly homogeneous in size (25–40µ). The structure of the dendritic profiles is simple and they carry only infrequent and small membranous appendages. Most synapses are axo-dendritic. The axon terminals are divided into three groups depending on the size and shape of the synaptic vesicles and the presence of post-synaptic specialization. A few glomerular axon terminals contacting with various structures are found. Small axon terminals located chiefly on dendrites and their appendages show degenerative changes 1–8 days after destruction of the red nucleus. As a rule the degenerating terminals contain round synaptic vesicles. The glomerular terminals do not degenerate.A. A. Bogomol'ets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 6, No. 6, pp. 610–618, November–December, 1974.     

Convergence of corticospinal and rubrospinal influences on cervical motoneurons

Synaptic responses of 121 identified cervical motoneurons to stimulation of the pyramidal tract and red nucleus were investigated by intracellular recording in cats. Responses of EPSP or EPSP-IPSP type were predominant in motoneurons of distal groups of muscles and proximal flexors, while responses of IPSP type were predominant in motoneurons of the proximal extensors. The minimal effective number of stimuli for most motoneurons was 2 or 3. The mean latent period, counted from the first stimulus in the series, was 7.86 msec for EPSPs for stimulation of the pyramidal tract and 7.91 msec for stimulation of the red nucleus, while the corresponding periods for IPSPs were 8.68 and 8.75 msec. The segmental delay of 1.3–2 msec for EPSPs and IPSPs generated in certain motoneurons in response to stimulation of both structures indicates that the shortest pathway for transmission of activity from the fibers of these tracts to the motoneurons may be disynaptic. At the same time, the possible presence of an additional neuron for most inhibitory pathways cannot be ruled out. Analysis of the results also suggests the presence of a common interneuronal apparatus for both systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.3, No.6, pp. 599–608, November–December, 1971.     

Experimental morphological study of primary afferent terminals at the base of the dorsal horn of the cat spinal cord

The distribution and ultrastructure of primary afferent terminals in the gray matter of the cervical and lumbar regions of the cat spinal cord were studied by the experimental degeneration method of Fink and Heimer. Most preterminals of primary afferents were shown to be concentrated in the region of the intermediate nucleus of Cajal (central part of Rexed's laminae VI–VII), in the substantial gelatinosa (laminae II–III), and in the nucleus proprius of the dorsal horn (central and medial parts of lamina IV). Fewer are found in the region of the motor nuclei. The number of degenerating axon terminals in the lateral parts of laminae IV and V differed: 31.5 and 0.4% respectively of all axon terminals. Many terminals of primary afferents in lamina IV contribute to the formation of glomerular structures in which they exist as terminals of S-type forming axo-axonal connections with other terminals. These results are in agreement with electrophysiological data to show that interneurons in different parts of the base of the dorsal horn differ significantly in the relative numbers of synaptic inputs formed by peripheral afferents and descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 406–414, July–August, 1973.     

Synaptic processes in spinal cord interneurons under rubrospinal effects

Synaptic processes of the spinal cord interneurons under rubrospinal effects have been investigated. A recording was made of 156 interneurons from the different parts of the gray matter, 111 of the interneurons were activated by descending effects from the red nucleus and 47 were not activated. Sixty nine interneurons of the first group responded only to rubrospinal impulsation and 42 neurons were also activated by afferent volleys. Interneurons activated only by the rubrospinal tract were located in the most lateral part of the VII Rexed's gray matter layer; the majority of interneurons activated by both rubrospinal and peripheral afferent volleys were located in the nucleus propius of the dorsal horn and the Cajal intermediate nucleus. The mean latencies of EPSP's and action potentials in interneurons activated only by a rubrospinal tract were 64±0.2 and 9.5±0.62 msec, respectively. The mean latency of EPSP's in motoneurons of flexor muscles was 10.3±0.62 msec and of IPSP's in motoneurons of extensor muscles, it was 11.5±1.28 msec. It is assumed that rubrospinal impulsation evokes excitatory PSP's in the motoneurons via the disynaptic pathway with the participation of special interneurons located in the lateral part of the VII layer. Inhibitory and late excitatory responses are, apparently, evoked via additional interneurons.A. A. Bogomolets Institute of Physiology of the Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 158–166, September–October, 1969.     

Unit responses in area 5b of the suprasylvian gyrus to stimulation of the posterior lateral thalmamic nucleus

In response to stimulation of the posterior lateral nucleus in unanesthetized cats immobilized with D-tubocurarine an evoked potential consisting of three components with a latent period of 3–5 msec appeared in area 5b of the suprasylvian gyrus. All three components were reversed at about the same depth in the cortex (1500–1600 µ). Reversal of the potential shows that it is generated in that area by neurons evidently located in deeper layers of the cortex and is not conducted to it physically from other regions. Responses of 53 spontaneously active neurons in the same area of the cortex to stimulation of the posterior lateral nucleus were investigated. A characteristic feature of these reponses was that inhibition occurred nearly all of them. In 22 neurons the responses began with inhibition, which lasted from 30 to 400 msec. In 30 neurons inhibition appeared immediately after excitation while one neuron responded by excitation alone. The latent periods of the excitatory responses varied from 3 to 28 msec. The short latent period of the evoked potentials and of some single units responses (3–6 msec) confirms morphological evidence of direct connections between the posterior lateral nucleus and area 5b of the suprasylvian gyrus. Repetitive stimulation of that nucleus led to strengthening of both excitation and inhibition. Influences of the posterior lateral nucleus were opposite to those of the specific nuclei: the posterior ventrolateral nucleus and the lateral and medial geniculate bodies. Stimulation of the nonspecific reticular nucleus, however, evoked discharges from neurons like those produced by stimulation of the posterior lateral nucleus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 502–509, September–October, 1973.     

Monosynaptic excitation of facial motoneurons during electrical stimulation of the red nucleus

Synaptic effects of the red nucleus on motoneurons of the facial nucleus were studied in cats. Impulses from the red nucleus activate motoneurons innervating the auricular, buccal, and orbicularis oculi muscles. Monosynaptic EPSPs appeared in all motoneurons which responded to stimulation. Their mean latent period was 1.5±0.04 msec, duration 12.3 ± 0.34 msec, and rise time between 1.5 and 3.2 msec. Repetitive stimulation of the red nucleus led to marked facilitation of the testing EPSP. Facilitation was maximal when the interval between stimuli was 3.5 msec; it was reduced by either a decrease or an increase in the interval. The functional role of the monosynaptic connections of neurons of the red nucleus and of the facial motoneurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 272–279, May–June, 1972.     

Corticofugal postsynaptic influences on red nucleus neurons

The responses of red nucleus neurons to stimulation of the sensorimotor cortex was studied on nembutal-anesthetized cats. Most of the rubrospinal neurons were identified according to their antidromic activation. Stimulation of the sensorimotor cortex was shown to evoke in the red nucleus neurons monosynaptic excitatory potentials with a latency of 1.85 msec, polysynaptic excitatory potentials (EPSP), and inhibitory postsynaptic potentials (IPSP) with a latency of 9–24 msec. The EPSP often produced spikes. The probability of generation of spreading excitation is greater with motor cortex stimulation. The monosynaptic EPSP are assumed to arise under the influence of the impulses arriving over the corticorubral neurons as a result of excitation of axodendritic synapses. The radial type of branching of red nucleus neurons facilitates the transition from electrotonically spreading local depolarization to an action potential triggered by the initial axonal segment. Polysynaptic EPSP and IPSP seem to be a result of activation of fast pyramidal neurons whose axon collaterals are connected via interneurons with the soma of the red nucleus neurons.L. A. Orbeli Institute of Physiology of the Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 43–51, January–February, 1971.     

Postsynaptic potentials of motoneurons evoked by rubrofugal impulsation in the hypoglossal nucleus of the cat

The effect of stimulation of the ipsilateral and contralateral red nuclei on motoneurons of the hypoglossal nucleus was studied in cats anesthetized with chloralose and pentobarbital. In 35 (69%) of the 51 motoneurons tested, PSPs were generated in response to stimulation of the red nuclei by series of 3 to 5 stimuli of threshold strength and with a frequency of 500–600/sec. Of this number, 33 motoneurons responded to stimulation by EPSPs, whose latent periods varied from 3.5 to 14.0 msec (mean value for the ipsilateral red nucleus 5.7±0.75, for the contralateral nucleus 6.8±0.8 msec), whereas two motoneurons responded (after 6.2 msec) by IPSPs. Of the 35 motoneurons responding to stimulation of the red nuclei, stimulation of the lingual nerve evoked EPSPs in 31 and IPSPs in 4 (two of them were inhibited by rubrofugal impulses). IPSPs were generated as a result of stimulation of the lingual nerve in 16 motoneurons which did not respond to rubrofugal impulses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 62–66, January–February, 1978.     

Unit responses of the first and second somatosensory areas to stimulation of the ventroposterior thalamic nucleus

Single unit responses of the first (SI) and second (SII) somatosensory areas to stimulation of the ventroposterior thalamic nucleus (VP) were investigated in cats immobilized with D-tubocurarine. In response to VP stimulation 12.0% of reacting SI neurons and 9.5% of SII neurons generated an antidromic spike. In most antidromic responses of both SI and SII neurons the latent period did not exceed 1.0 msec. The minimal latent period of spike potentials during orthodromic excitation was 1.5 msec in SI and 1.7 msec in SII. Neurons with an orthodromic spike latency of not more than 3.0 msec were more numerous in SI than those with a latency of 3.1–4.5 msec. The ratio between the numbers of neurons of these two groups in SII was the opposite. In SII there were many more neurons with a latency of 5.6–8.0 msec than in SI. EPSPs appeared after a latent period of 1.1–9.0 msec in SI and of 1.4–6.6 msec in SII. The latent period of IPSPs was 1.5–6.8 msec in SI and 2.2–9.4 msec in SII. The relative importance of different pathways for excitatory and inhibitory influences of VP on SI and SII neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 115–121, March–April, 1976.     

Pyramidal influences on interneurons of spinal segmentary reflector arcs in cat

Microelectrode discharges of potentials have been realized from segmentary interneurons of the dorsal horn and intermediate nucleus of the spinal cord in cat at the L₆–L₇ level by electrical stimulation of the sensorimotor region of the brain cortex. It has been established that corticifugal influences on segmentary interneurons of the system of the flexor reflex and on neurons activated by high threshold muscle afferents (groups Ib, II, and III), or high threshold cutaneous afferents are predominantly excitatory. Interneurons activated by muscle afferents of group Ia or by the lowest threshold cutaneous fibers are weakly subjected to pyramidal influences. The mean latencies of excitatory postsynaptic potentials (EPSP's) and discharges evoked under the influence of pyramidal volley, for the neurons under study in the system of afferents of the flexor reflex are equal to 11.8±2.6 and 20.1±1.8 msec, respectively; for interneurons, excited only by high threshold muscle afferents, they are equal to 15.5±3.6 and 16.3±2.2 msec, respectively; and for interneurons, excited by high threshold cutaneous fibers they are equal to 11.8±2.6 and 18.3±1.4 msec, respectively. Possible pathways of activating segmentary interneurons from the lateral sensorimotor region of the brain cortex have been discussed.The A. A. Bogomolets Institute of Physiology, Academy of Sciences, Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 17–25, January–February, 1970.     

Single unit responses of the reticular and ventral anterior nuclei of the thalamus to electrical stimulation of the centrum medianum

In acute experiments on cats anesthetized with thiopental (30–40 mg/kg, intraperitoneally) and immobilized with D-tubocurarine (1 mg/kg) responses of 145 neurons of the reticular and 158 neurons of the ventral anterior nuclei of the thalamus to electrical stimulation of the centrum medianum were investigated. An antidromic action potential appeared after a latent period of 0.3–2.0 msec in 4.1% of cells of the reticular nucleus and 4.4% of neurons of the ventral anterior nucleus tested in response to stimulation. The conduction velocity of antidromic excitation along axons of these neurons was 1.7–7.6 m/sec. Neurons responding with an antidromic action potential to stimulation both of the centrum medianum and of other formations were discovered, electrophysiological evidence of the ramification of such an axon. Altogether 53.8% of neurons of the reticular nucleus and 46.9% of neurons of the ventral anterior nucleus responded to stimulation of the centrum medianum by orthodromic excitation. Among neurons excited orthodromically two groups of cells were distinguished: The first group generated a discharge consisting of 6–12 action potentials with a frequency of 130–640 Hz (the duration of discharge did not exceed 60 msec), whereas the second responded with a single action potential. Inhibitory responses were observed in only 0.7% of neurons of the reticular nucleus and 4.4% of the ventral anterior nucleus tested. Afferent influences from the relay nuclei of the thalamus, lateral posterior nucleus, and motor cortex were shown to converge on neurons responding to stimulation of the centrum medianum.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 36–45, January–February, 1980.     

Unit responses of the ventral posterior and ventral lateral thalamic nuclei to electrical stimulation of the thalamic reticular nucleus

A microelectrode investigation was made of responses of 72 physiologically identified neurons of the ventral posterior (VP) and 116 neurons of the ventral lateral (VL) thalamic nuclei to electrical stimulation of the reticular (R) thalamic nucleus. Mainly those neurons of VP and VL (73.7 and 86.2% respectively) which responded to stimulation of the first motor area and nucleus interpositus of the cerebellum responded to stimulation of R; 19.8% of VL neurons tested responded to stimulation of R by an antidromic action potential with latent period of 0.5–2.0 msec and 46.6% of neurons responded by orthodromic excitation; 23% of orthodromic responses had a latent period of 0.9–3.5 msec and 77% a latent period of 4.0–21.0 msec; 19.8% of VL neurons tested were inhibited. Among IPSPs recorded only one was monosynaptic (1.0 msec) and the rest polysynaptic. It is postulated that both R neurons are excitatory and that the inhibition which develops in VL neurons during stimulation of R are connected mainly with activation of inhibitory interneurons outside the reticular nucleus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 477–485, September–October, 1977.     

Synaptic activation of thoracic interneurons by reticulospinal fibers of the lateral funiculus

Synaptic responses of different functional groups of interneurons in segments T10 and T11 to stimulation of the ipsilateral and contralateral medullary reticular formation were investigated in anesthetized cats with only the ipsilateral lateral funiculus remaining intact. Activation of reticulospinal fibers of the lateral funiculus with conduction velocities of 30–100 m/sec was shown to induce short-latency and, in particular, monosynptic EPSPs in all types of cells tested: in interneurons excited by group Ia muscle afferents, in cells activated only by high-threshold cutaneous and muscle afferents (afferents of the flexor reflex), in cells activated mainly by descending systems, and, to a lesser degree, in neurons connected with low-threshold cutaneous afferents. These cell populations are located mainly in the central and lateral parts of Rexed's lamina VII. Most neurons in laminae I–V of the dorsal horn, except six cells located in the superficial layers of the dorsal horn, received no reticulofugal influences. The functional organization of connections of the lateral reticulospinal tract with spinal neurons is discussed and compared with the analogous organization of the medial reticulospinal tract, and also of the "lateral" (cortico- and rubrospinal) descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 150–161, March–April, 1978.     

Organization of bilateral spinal projections to the lateral reticular nucleus of the rat

The present study was carried out to analyze the topography of bilateral spinal projections to the lateral reticular nucleus (LRN). We used retrograde transport of fluorescent tracers Fast Blue and Diamidino Yellow to identify spinal neurons projecting to the ipsilateral and/or contralateral LRN, as well as orthograde transport of Phaseolus vulgaris leucoagglutinin to identify the LRN areas where spinoreticular axons terminate. Orthograde labeling confirmed that bilateral spinoreticular projections coming from cervical and upper-thoracic segments terminate in the magnocellular division of LRN, while those coming from the lower-thoracic, lumbar and sacral segments end in the parvocellular division of the nucleus; only a sparse spinal input has been observed in the subtrigeminal division of LRN. Retrograde labeling showed that labeled neurons were present at all spinal levels and in particular large numbers in the cervical and lumbar enlargements. Retrogradely single-labeled cells were located, with contralateral predominance, in all segments of the spinal cord, within laminae IV, V, VI, VIII, and X, whereas in laminae III and VII labeled neurons were mainly observed ipsilaterally. Furthermore, a small fraction of double-labeled cells (7.4%) was observed throughout the spinal cord, mainly in laminae III, IV, VII and VIII.     

Neuronal responses of the reticular and anterior ventral thalamic nuclei to stimulation of the thalamic ventrolateral nucleus and motor cortex

Responses of 137 neurons of the rostral pole of the reticular and anterior ventral thalamic nuclei to electrical stimulation of the ventrolateral nucleus and motor cortex were studied in 17 cats immobilized with D-tubocurarine. The number of neurons responding antidromically to stimulation of the ventrolateral nucleus was 10.5% of all cells tested (latent period of response 0.7–3.0 msec), whereas to stimulation of the motor cortex it was 11.0% (latent period of response 0.4–4.0 msec). Neurons with a dividing axon, one branch of which terminated in the thalamic ventrolateral nuclei, the other in the motor cortex, were found. Orthodromic excitation was observed in 78.9% of neurons tested during stimulation of the ventrolateral nucleus and in 52.5% of neurons during stimulation of the motor cortex. Altogether 55.6% of cells responded to stimulation of the ventrolateral nucleus with a discharge of 3 to 20 action potentials with a frequency of 130–350 Hz. Similar discharges in response to stimulation of the motor cortex were observed in 30.5% of neurons tested. An inhibitory response was recorded in only 6.8% of cells. Convergence of influences from the thalamic ventrolateral nucleus and motor cortex was observed in 55.7% of neurons. The corticofugal influence of the motor cortex on responses arising in these cells to testing stimulation of the ventrolateral nucleus could be either inhibitory or facilitatory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 460–468, September–October, 1978.     

Character of activation of medullary reticulospinal neurons by collaterals of pyramidal fibers

The character of activation of medullary reticulospinal neurons by collaterals of pyramidal fibers was investigated in cats anesthetized with pentobarbital (40 mg/kg) or a mixture of chloralose (45 mg/kg) and pentobarbital (15 mg/kg). The experiments were carried out on animals after preliminary destruction of the contralateral red nucleus and division of the ipsilateral dorsolateral fasciculus in segment C₄. A conditioning technique showed that pre- and postsynaptic effects arising in the medullary gigantocellular nucleus to stimulation of the cortex and of the isolated dorsolateral funiculus are due to activation of collaterals of pyramidal fibers projecting into the brain stem. In most reticulospinal neurons tested, stimulation of the fasciculus induced monosynaptic EPSPs. Their generation was due to influences transmitted via fast- and slow-conducting pyramidal fibers. Pyramidal fibers with different conduction velocities are distributed irregularly in the pyramidal tract in the cervical region of the spinal cord. Mainly slowly-conducting fibers are found in its medial zones and fast-conducting pyramidal fibers in its lateral zones. The results are evidence that in cats fibers of the pyramidal tract, running into the spinal cord, can activate medullary reticulospinal neurons directly.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 495–503, September–October, 1977.     

Effect of stimulation of the caudate nucleus on activity of neurons of the globus pallidus

Activity of neurons of the globus pallidus was recorded extracellularly during stimulation of the caudate nucleus. It is demonstrated that background activity (BA) of most neurons of the globus pallidus is depressed under these conditions, which is regarded as a manifestation of inhibition of the investigated neurons. The period of BA depression varied in different cells from 60 to 500 msec. In some cases this period was preceded by emergence of an action potential with a latent period of 10–20 msec. In addition to inhibition of the activity of globus pallidus neurons during stimulation of the caudate nucleus, it was possible to record evoked responses of the given neurons in the form of group discharges with a latent period of 18–40 msec and single action potentials with a latent period of 50–100 msec. The neurons that reacted with a shorter latent period were localized at the lateral limit of the globus pallidus, whereas neurons with other kinds of responses were distributed in the globus pallidus comparatively evenly.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 202–209, September–October, 1969.