Functional properties of propriospinal pathways of the dorsolateral tract of the cat spinal cord

The characteristics of conduction of the excitation wave along propriospinal fibers of the dorsolateral tract of the spinal cord were studied in cats anesthetized with pentobarbital. At a preliminary operation, 10–18 days beforehand, lateral hemisection of the spinal cord was performed, cranially in the lumbar division and caudally and cranially in the cervical division to the segments to be studied, leading to degeneration of the long descending and ascending fibers. During stimulation, the dorsolateral tract developed a composite response consisting of a positive-negative wave recorded up to 60–65 mm (4 or 5 segments) from the point of stimulation. The mean conduction velocity of this wave in the lumbar division was 37.9 m/sec compared with 44.5 m/sec in the cervical division. From its properties as a whole this wave can be regarded as the result of excitation of relatively fast-conducting propriospinal fibers of the dorsolateral tract. If the strength of stimulation was increased, late components began to appear in the response. These were evidently connected with excitation of thinner propriospinal fibers and synaptic activation of other other groups of spinal neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 54–60, January–February, 1973.     

Spatial distribution of descending propriospinal tract neurons in the cat spinal cord

Quantitative estimates of the density of distribution of interneurons forming descending intersegmental connections in the cat spinal cord were obtained. Neurons were labeled by retrograde axonal transport of horseradish peroxidase injected unilaterally at different segmental levels. The mean number of labeled units per section 50 µ thick, in a given zone, was used as the measure of density. The density of distribution of the propriospinal neurons forming the longest tracts between the cervical and lumbosacral regions of the cord was found to be about half the density of distribution of neurons with short (not more than two segments) axons, and to be several times less than the corresponding value for neurons with axons of intermediate length. No marked local peaks of density of distribution of long-axon neurons were found at the level of the brachial enlargement. The number of neurons with crossed axons in most segments was close to half of the total number of propriospinal units. Zones of transverse section of the spinal cord with maximal concentrations of neurons forming direct and crossed propriospinal tracts of different lengths were determined at different levels. Correlation between the quantitative composition of propriospinal neuron populations with characteristics of influences transmitted by these populations is examined.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 96–105, January–February, 1984.     

Synaptic links of propriospinal neurons of the lumbar section of the cat spinal cord

The distribution of propriospinal fiber terminals of the lateral funiculus in the lumbar segments of the cat spinal cord was examined by light and electron microscopy. For the selective demonstration of these terminals, preliminary hemisectioning of the brain at the boundary of the thoracic and lumbar segment, eliminating all the long descending pathways, and subsequent hemisectioning or sectioning of the lateral funiculus at the level of the third lumbar segment was carried out. It was established by staining the degenerating endings (by the Fink—Heimer method) that the terminals of the descending and ascending propriospinal fibers, which form part of the lateral and ventral funiculi, are located mainly in the lateral and medial parts of lamina VII and the dorsal section of lamina VIII, according to Rexed, as well as in the regions adjacent to the dorsolateral and ventromedial motor nuclei. A large number of these terminals is found in the corresponding regions of the gray matter on the contralateral side of the brain. Since, in the case of selective injury of the lateral funiculus the number of degenerating terminals in lamina VIII is noticeably decreased, it can be assumed that the propriospinal neuron terminals of the ventral funiculus are concentrated mainly in lamina VIII. The axons of the propriospinal neurons extend over several segments both in the ascending and in the descending directions. It was shown in an electron microscopic study of the regions in which most of the propriospinal terminals are located that these terminals are of an axo-dendritic nature and terminate in the dendrites of both inter- and motor neurons. Their degeneration can be of the "light" or "dark" type.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 401–407, July–August, 1971.     

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.     

Synaptic responses of propriospinal neurons to stimulation of the stepping strip of the dorsolateral funiculus in cats

Synpatic responses were recorded extracellularly from single neurons at levels T12–T13 in response to microstimulation of the stepping strip of the dorsolateral funiculus in the thoracic and cervical portions of the spinal cord in cats decerebrated at the precollicular level [4]. The latent periods of these responses increased when the distance between the stepping point and recording point exceeded 20 mm, and when two stimuli had to be applied in order to evoke responses. Axons of neurons respondingtrans-synaptically to stimulation of the stepping strip were located on the boundary between the lateral and ventral funiculi close to the gray matter. Antidromic responses of neurons sending their axons in the caudal direction were found on average in 37% of cases, provided that the distance between the recording and stimulation points did not exceed 40 mm. Half of the neurons which generated synaptic responses to stimulation of spinal stepping points could be excited also by a series of three to six stimuli, applied to the mesencephalic locomotor point [15]. It is suggested that the neurons discovered may participate in the spread of activity toward the generator of stepping movements of the hind limb.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 270–278, March–April, 1985.     

Synaptic organization of supraspinal control over propriospinal ventral horn interneurons in cat and monkey spinal cord

Synaptic responses evoked in propriospinal neurons of the upper lumbar segments (L₃–L₄) by reticulo-, vestibulo-, and corticospinal impulses were studied in experiments on cats and monkeys. Propriospinal cells, identified by antidromic stimulation, were stained with Procion red, so that they could be localized in the different zones of the ventral horn. Monosynaptic reticular and vestibular excitatory influences were discovered in cats; convergence of these influences on the same neurons was demonstrated. In monkeys bulbospinal monosynaptic effects were supplemented by monosynaptic influences arriving from the motor cortex; convergence of monosynaptic excitatory influences from all supraspinal sources studied was found on some propriospinal neurons. The propriospinal neurons studied also had synaptic inputs from primary afferents.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 177–184, March–April, 1977.     

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.     

Synaptic effects evoked in motoneurons by stimulation of single propriospinal neurons

Experiments on cats with simultaneous extracellular recording, stimulation of single propriospinal neurons, and intracellular recording of unitary postsynaptic potentials from motoneurons, followed by computer averaging showed that direct stimulation of individual propriospinal cells receiving mono- and disynaptic influences from the medial reticular formation can evoke monosynaptic EPSPs and IPSPs in lower lumbar motoneurons. The amplitude of these EPSPs was 49.6±6.0 and of the IPSPs 28.9±2.9 µV and their synaptic delay was 0.34±0.05 msec. The same propriospinal neuron of the ventral horn of the upper lumbar segments may be connected with several motoneurons of the hind limb muscles.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 300–306, May–June, 1977.     

Postsynaptic effects evoked by activation of long propriospinal pathways in cervical spinal neurons in cats

Effects induced in motoneurons and interneurons of the cervical enlargements of the cat spinal cord by stimulation of the lateral and ventral funiculi at the lower thoracic level were studied under conditions producing degeneration of fibers of descending brain systems. Stimulation of this sort evoked PSPs (mainly of mixed character) in 57 of 90 motoneurons tested. In nine motoneurons the primary response consisted of monosynaptic EPSPs evoked by activity of fibers of the lateral funiculus, and in the rest it consisted of polysyanptic (at least disynaptic) EPSPs and IPSPs. Polysynaptic effects arising in the neuron in response to stimulation of the lateral and ventral funiculi usually differed only quantitatively. The intensity of excitatory synaptic action on motoneurons of the proximal muscle (especially thoracid) was much greater than that on motoneurons of distal muscles. Nearly all motoneurons with no synaptic action belonged to the latter group. Stimulation of the lateral and ventral funculi facilitated synaptic action induced in motoneurons by stimulation of high-threshold segmental afferents and led to excitation of interneurons located in the vectral quadrant, and had no effect on interneurons in the dorsal regions of gray matter. These effects are regarded mainly as the result of excitation of long ascending propriospinal pathways in the cervical parts of the cord; it is also postulated that some of them are evoked by the arrival of activity along collaterals of descending propiospinal pathways to the neurons in this region.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 339–347, July–August, 1979.     

Experimental morphological study of endings of propriospinal fibers of the lateral funiculus in the cat cervical spinal cord

The distribution and ultrastructure of terminals of the propriospinal fibers of the lateral funiculus in the cervical segments of the cat spinal cord were studied by the experimental degeneration method. A preliminary lateral hemisection of the spinal cord was carried out 5–6 months earlier at the level of segments C2 or C3 to destroy all the long descending pathways; the lateral funiculus was then divided at the level of C4 or C5. It was shown by the method of Fink and Heimer that terminals of descending and ascending propriospinal pathways damaged by the second division are distributed in the gray matter ipsilaterally in the lateral zones of Rexed's laminase V–VII and also in the dorsolateral motor nuclei. An electron-microscopic study showed that the synapses of the degenerating terminals are mainly axo-dendritic in type and account for 14.5% of the total number of terminals counted. Residual synaptic vesicles in these terminals were spherical in shape. The mean diameter of the degenerating myelinated propriospinal fibers in the lateral funiculus was 10±3 µ. The results of this investigation were compared with those of electrophysiological investigations of the function of propriospinal neurons.     

Synaptic processes in pericruciate cortical neurons evoked by pyramidal tract stimulation in cats

In cats anesthetized with chloralose and pentobarbital and immobilized with D-tubocurarine activity of 423 pericruciate cortical neurons was recorded (342 extra- and 81 intracellularly); 78 neurons had spontaneous activity. Stimulation of the pyramidal tract evoked antidromic action potentials in the pyramidal neurons with a latent period of 0.5–16.0 msec. Recurrent and lateral PSPs also developed both in pyramidal and in unidentified neurons in all layers of the cortex; IPSPs were recorded in 46.7% of neurons, EPSPs in 21.0%, mixed reponses in 26.0%, and no visible changes were found in 6.3%. The latent period of the IPSPs was 1.5–14.0 msec, their amplitude 1.3–17.0 mV, their rise time from 4 to 18 msec, and their duration 18–120 msec (sometimes up to 250–500 msec). In 30% of cases in which IPSPs appeared, their course was divided into two phases: fast (duration 10–20 msec) and slow. EPSPs developed after a latent period of 2.6–29.0 msec; their amplitude was 1.0–7.8 mV and their duration from 10.0 to 50.0 msec. In 51.2% of spontaneously active neurons the antidromic volley inhibited their activity in the course of 200–400 msec, in 19.5% it stimulated their activity, in 7.4% it had a mixed effect, and in 21.9% no visible change took place in their activity. The role and participation of axon collaterals of pyramidal neurons and of the interneuronal system in the formation of these processes are discussed.     

Synaptic responses of medulla oblongata neurons to stimulation of the spinal stepping atria in the cat

Synaptic responses of medulla oblongata (bulbar) neurons to microstimulation of stepping points in the spinal dorsolateral funiculi were recorded in decrebrate cats. Upon stimulation of the stepping point both in the ipsi- and contralateral funiculi, 40% of the neurons generated synaptic responses; the remaining cells responded to stimulation of only one stepping point. A part of the bulbar neurons responds to stimulation of stepping points both at the C₂ and Th₁₂ level. The latent periods of the synaptic responses of the bulbar neurons to stimulation of the stepping point at the C₂ level were in the 2–10 msec range. The data obtained indicate that bulbar neurons, along with propriospinal neurons, can participate in evoking locomotion upon stimulating the stepping point.Institute of Information Transmission Problems, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 328–333, May–June, 1991.     

Responses of motor neurons of lumbar section of spinal cord elicited by the activity of the propriospinal pathways

We have carried out intracellular recording from the motor neurons of the lumbar section of the cat spinal cord with electrical stimulation of the propriospinal axons descending in the dorsolateral funiculus. To prevent activation of the long descending pathways of the lateral funiculus, ipsilateral hemisectioning of the spine was performed in the segments L₁-L₂ 10–14 days before the experiment. Stimulation of the dorsolateral funiculus in two segments cranial to the point of recording elicited in the flexor motor neurons essentially e.p.s.p. and in the extensor neurons i.p.s.p. with a latent period, on the average, of 1.97 and 1.93 msec, respectively. The amplitude of such p.s.p. considerably rose with rise in the frequency of stimulation of the funiculus to 50–100 a second. Activation of the segmental interneurons was observed only in a few cases. It is assumed that the synaptic processes elicited in the lumbar motor neurons are the result of the monosynaptic influences of the propriospinal neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 5–14, July–August, 1969.     

离体培养的小鼠脊髓固有神经元的突触构筑

An electron microscopic analysis of the synaptic architecture in propriospinal neurons of cultured fetal mouse spinal cord has been undertaken. The size of the perikarya in the cultured spinal cord represents a range from small- to medium sized neurons, which form many synapses each other. There are many axo-dendritic and axo-somatic synapses in the culture but direct dendro-dendritic apposition is rarely seen. Four morphological types of synaptic boutons, S, F, M and G are classified according to criteria used by previous investigators. The ultrastructural details available suggest that the propriospinal neurons receive synaptic input from propriospinal fibers through simple synapses. It may indicate that their impulses can be controlled only postsynaptically.     

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.     

Effect of epidural spinal cord stimulation on the activity of lateral vestibular nucleus neurons in the cat

The activity of neurons in Deiters' lateral vestibular nucleus was recorded in decerebrate cats before, during and after spinal cord stimulation. An almost equal number of units were inhibited and excited early during stimulation. Later during stimulation the majority of units was inhibited. Early after cessation of stimulation an ever larger number of units were inhibited to an even larger extent (for about 2 imp/s on the average). Later after stimulus cessation the predominant inhibitory effect could still be noted, as well as excitation in some units. The results could support the hypothesis that the inhibition of Deiters' neurons during and for some time after epidural cord stimulation may play a part in the decrease of limb spasticity. The mechanism of inhibitory and excitatory unitary responses, side effects during stimulation and differences between the experimental model and human state are discussed.     

Respiratory resetting induced by spinal cord stimulation in the cat

Electrical stimulation (50-150 microA, 0.5-ms duration, 3-300 Hz) was performed within three different regions (lateral, ventrolateral, and ventral) of the C2-C3 spinal cord of decerebrate, vagotomized, paralyzed, and artificially ventilated cats. Spinal cord stimulation sites were located by inserting monopolar or bipolar stimulating electrodes either at the dorsolateral sulcus or at least 1 mm medial or lateral to the sulcus. With stimulation at each site, alterations in respiratory rhythm, orthodromic phrenic nerve responses, and antidromic activation of medullary respiratory-modulated neurons were examined. Phrenic nerve responses to cervical spinal cord stimulation consisted of an early excitation (2-4 ms) and/or a late excitation (4-8 ms). Stimulation of the lateral region evoked the greatest amplitude early response and stimulation of the ventrolateral region produced the greatest late excitation. All three stimulus sites elicited antidromic activation of some respiratory-modulated neurons in the dorsal (DRG) and ventral respiratory groups (VRG). The lateral region was the least effective resetting site, and it had the highest incidence of antidromic activation of both DRG and VRG neurons. The ventrolateral region of the cervical spinal cord was the most effective resetting site, but it had the lowest incidence of antidromic activation of DRG respiratory-modulated neurons. In addition, resetting responses were observed with spinal cord stimulation at similar sites in the thoracic and lumbar spinal cord regions thought to be devoid of inspiratory bulbospinal axons.(ABSTRACT TRUNCATED AT 250 WORDS)