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.     

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.     

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.     

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.     

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.     

Synaptic processes in neurons of the cervical enlargement of the cat spinal cord during stimulation of propriospinal pathways of the dorsolateral tract

Responses of motoneurons and interneurons of the cervical enlargement of the cat spinal cord were studied by a microelectrode technique during selective stimulation of propriospinal fibers of the dorsolateral tract of the lateral white column. The long descending and ascending pathways were blocked by preliminary (10–16 days earlier) hemisection of the spinal cord cranially and caudally to the segments studied. Stimulation of the dorsolateral tract at a distance of 15–25 mm from the site of recording evoked complex postsynaptic potentials consisting of several successive waves in the motoneurons. The character of the PSPs was not clearly linked with the function of the motoneurons. By their latent periods the components of the PSPs could be placed in three groups. The "primary" components were reproduced in response to stimulation at 50–100/sec whereas the "secondary" and "tertiary" components were weakened or blocked. It is postulated that the "primary" components are evoked through monosynaptic connections between propriospinal fibers of the dorsolateral tract and motoneurons of the forelimb muscles, while the late components are evoked through polysynaptic pathways, including segmental interneurons. Many of these interneurons, located in the ventral horn and intermediate zone, were strongly excited during stimulation of the dorsolateral tract.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 61–69, January–February, 1973.     

Extensive fusion of mitochondria in spinal cord motor neurons

The relative roles played by trafficking, fission and fusion in the dynamics of mitochondria in neurons have not been fully elucidated. In the present study, a slow widespread redistribution of mitochondria within cultured spinal cord motor neurons was observed as a result of extensive organelle fusion. Mitochondria were labeled with a photoconvertible fluorescent protein (mitoKaede) that is red-shifted following brief irradiation with blue light. The behavior of these selectively labeled mitochondria was followed by live fluorescence imaging. Marking mitochondria within the cell soma revealed a complete mixing, within 18 hours, of these organelles with mitochondria coming from the surrounding neurites. Fusion of juxtaposed mitochondria was directly observed in neuritic processes at least 200 microns from the cell body. Within 24 hours, photoconverted mitoKaede was dispersed to all of the mitochondria in the portion of neurite under observation. When time lapse imaging over minutes was combined with long-term observation of marked mitochondria, moving organelles that traversed the field of view did not initially contain photoconverted protein, but after several hours organelles in motion contained both fluorescent proteins, coincident with widespread fusion of all of the mitochondria within the length of neurite under observation. These observations suggest that there is a widespread exchange of mitochondrial components throughout a neuron as a result of organelle fusion.     

Relationship between the activity of postsynaptic spinal cord elements and propriospinal and spino-bulbo-spinal reflexes.

The relationship between the activity of the lumbar spinal interneurones and propriospinal (PS) and spino-bulbo-spinal (SBS) efferent reflex responses evoked by somatic (muscle, skin) and splanchnic nerve stimulation was studied in chloralose-anaestetized adult cats. During stimulation of one somatic nerve, the postsynaptic cord elements could be divided into three groups, according to whether their activity was was synchronous with the PS component of the efferent discharge (PS group), with the SBS component (SBS group) or with both (PS-SBS-group). Group SBS and PS-SBS interneurones were localized in the ventral quadrant of the grey matter. On stimulation of different nerves, the same interneurone could in one case respond synchronously with the PS component of the efferent discharge and in another with the SBS component. The membrane of units which did not generate propagated spike potentials during PS or SBS reflex activity was hyperpolarized in this period, or failed to display changes characteristic for postsynaptic inhibition. Convergence of somatic and visceral afferentation was observed in all three groups of postsynaptic elements. In type PS-SBS and SBS units it was massive (occurring in 85% and 100% of the cases respectively). The results confirmed the intimacy of functional contact of PS and SBS systems activated by somatic and visceral afferents.     

Control of respiratory motor pattern by sensory neurons in spinal cord of lamprey

Summary Extracellular stimulation over the dorsal funiculus in the spinal cord of lampreys was found to selectively activate prolonged episodes of fictive arousal respiration (Figs. 1, 3). The induced episodes showed comparable increases in cycle frequency and motoneuron burst duration to the spontaneous arousal pattern observed in isolated brain preparations (Fig. 2). Intracellular stimulation of primary sensory neurons with axons in the dorsal funiculus, called dorsal cells, also elicited the arousal pattern (Fig. 4). Mechanoreceptive dorsal cells respond to cutaneous stimulation. When mechanical stimuli were applied to the skin of intact lampreys (Fig. 6) or to lampreys with ipsilateral vagotomy, arousal respiration was induced (Figs. 7, 8). Bilateral, but not unilateral, trigeminal lesion blocked dorsal cell induction of the arousal response (Fig. 5). Spontaneous arousal respiration was recorded from intact, unrestrained lampreys (Fig. 9). These results suggest that fictive arousal respiration is the in vitro correlate of natural arousal respiration in lampreys, and that one mechanism leading to arousal respiration may be the activity of sensory dorsal cells. A model for respiratory motor pattern switching in lamprey is proposed. The model suggests that the normal and arousal patterns are produced by separately engaging rostral or caudal pattern generators in the medulla, rather than by modifying one pattern generator (Fig. 10).     

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.     

Properties of axons of sympathetic preganglionic neurons in the cat lumbar spinal cord

Responses arising in ventral root filaments and antidromic discharges of single sympathetic preganglionic neurons in the lateral horn of gray matter in segment L₂ of the cat spinal cord were recorded during stimulation of the white rami communicantes in the same segment. Conduction velocities, thresholds, and refractory periods were determined for individual groups of sympathetic preganglionic fibers. Excitation was conducted more slowly along the intramedullary part of the axons of some sympathetic neurons than along the extramedullary part. In a third group of neurons studied the second antidromic discharge appeared in response to paired stimulation if the interstimulus interval was appreciably longer than their refractory period. It is postulated that axons of sympathetic preganglionic neurons in the lumber spinal cord have a thin intramedullary part and are supplied with recurrent collaterals.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 6, No. 2, pp. 143–151, March–April, 1974.     

Influence of afferent impulses from the nerves of the anterior limbs on the insertion neurons of the lumbar section of the spinal cord

In anesthetized cats in conditions of muscular relaxation we have studied the participation of the interneurons of the lumbar section of the spinal cord in the interaction of the FRA systems of the fore and hind limbs. Using microelectrodes we have made extra- and intracellular recordings of the potentials. It has been shown that from the flexor afferents of the fore limbs both facilitating and inhibitory influences are transmitted. The former are expressed in increased frequency of the background impulse activity of the neurons, in the appearance of evoked responses of the "silent" cells and intensification of the test responses for short time intervals with paired heteronymous stimulation. The inhibitory influences prevail over the facilitating and are manifest in depression of the background activity and evoked segmental responses of the neurons. The maximum inhibition of the segmental responses was noted for intervals of 40–140 msec. The duration of inhibition varied from 100–500 msec and more. Depending on the intensity and duration of the inhibitory influences two groups of interneurons have been isolated. The role of the pre- and postsynaptic mechanisms in the transmission of inhibitory influences from the afferents of the fore limbs on the afferents of the hind limbs is discussed.Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 235–242, November–December, 1969.