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 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 activation of thoracic spinal interneurons by reticulospinal pathways

Synaptic processes of 119 thoracic spinal interneurons (T10–11) were investigated in anesthetized cats in response to stimulation of the medial and central zones of the gigantocellular nucleus in the medulla and the ventral columns of the spinal cord. Fast (90–130 m/sec) reticulospinal fibers running in the ventral column were found to produce monosynaptic or disynaptic excitation of interneurons of Rexed's layers VII–VIII, which are connected monosynaptically with group I muscle afferents, and interneurons excited both by group I muscle afferents and low-threshold cutaneous afferents. In most neurons of layer IV, connected monosynaptically with low-threshold cutaneous afferents, and in neurons of layers VII–VIII excited by afferents of the flexor reflex no marked postsynaptic processes were observed during stimulation of the reticular formation. Excitatory, inhibitory, and mixed PS Ps during activation of reticulospinal fibers were found in 14 neurons, high-threshold afferents in which evoked predominantly polysynaptic IPSPs. Seventeen neurons activated monosynaptically by reticulospinal fibers and not responding to stimulation of segmental afferents were found in the medial part of the ventral horn (layers VII–VIII).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 566–578, November–December, 1972.     

Synaptic processes produced in cat rubrospinal neurons by stimulating the cerebellar nucleus interprositus

The activity produced in red nucleus rubrospinal neurons by stimulating the cerebellar nucleus interpositus was investigated in cats anesthetized with nembutal. Analysis of field potentials together with summated and single EPSP following paired and frequency stimulation of this structure revealed facilitation at cerebello-rubral synapses. It was found that this facilitation was not mediated by changes in presynaptic volleys. It is suggested that modification of the effectiveness of transmission is determined by characteristic features of the operation of cerebellar synapses on red nucleus neurons.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 630–636, September–October, 1987.     

红核脊髓运动诱发电位与脊髓损伤的关系

目的: 探讨一种可以敏感地反映脊髓损伤程度的客观、定量的电生理学指标.方法: 采用Wrathall等人描述的重力损伤法制备大鼠脊髓胸段(T8)分级损伤模型,通过测量损伤动物红核-脊髓运动诱发电位(MEPs)的变化,并与动物运动行为和组织形态学检查结果进行比较,分析红核-脊髓MEPs与脊髓分级损伤的关系.结果: 在给予红核刺激后,假损伤组红核-脊髓MEPs出现5～7个正波和4～5个负波,峰-峰总幅度值(简称总峰值)为(195.25±34.35)μV,峰潜伏时为(1.57±0.15)ms.随损伤程度加大,总峰值明显减少,而峰潜伏时明显延长.红核-脊髓MEPs总峰值与观察期末的BBB评分(r=0.79)以及损伤中心处的残余面积(r=0.87)显著相关;峰潜伏时与观察期末的BBB评分(r=-0.88)以及损伤中心处的残余面积(r=-0.86)也有显著的相关性.结论: 红核-脊髓MEPs总峰值和峰潜伏时两项指标可以敏感地反映脊髓分级损伤程度、运动功能和形态学情况,是监测胸段脊髓损伤程度的客观、定量、精细的电生理指标.     

Mechanism of inhibition following reflex discharge in spinal cord interneurons

Using the method of microelectrode (intracellular and extracellular) recording, the mechanism of inhibition following reflex discharge in interneurons of the lumbosacral section of the spinal cord of cats on activation of cutaneous and high-threshold muscle afferents was studied. It was shown that the postdischarge depression of the reflex responses 10–20 msec after the moment of activation of the neuron is due to afterprocesses in the same neuron and presynaptic pathways. The depression of spike potentials from the 20th to the 100th msec is produced by inhibitory postsynaptic potentials (IPSP). During the development of IPSP the inhibition of spike potentials can be due to both a decrease of the depolarization of the postsynaptic membrane below the critical threshold and a decrease of sensitivity of the cell membrane to the depolarizing action of the excitatory postsynaptic potential (EPSP). At intervals between the stimuli of 30–100 msec the duration of EPSP after the first stimulus does not differ from that after the second stimulus. Hence, it is suggested that the presynaptic mechanisms do not play an essential part in this type of inhibition of interneurons. The inhibition following the excitation favors the formation of a discrete message to the neurons of higher orders.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 3–9, January–February, 1970.     

Inhibition of crossed caudal interneurons by lateral interneurons in lamprey spinal cord during fictive locomotion

Templates of the membrane potential profiles from lateral (LI) interneurons and motoneurons during glutamate- and N-methyl-D-aspartate (NMDA)-induced fictive locomotion showed pronounced plateau phases. In contrast, crossed caudal (CC) interneurons had a less obvious and steeper plateau region that was followed by a clear notch coinciding with the end of the lateral interneuron plateau phase. These results indicate a significant inhibitory input from LI to CC interneurons.     

Accumulation of 3H-glycine in interneurons of the cat spinal cord

Summary After in vivo njections of ³H-glycine into the cat spinal cord autoradiography at the light and electron microscopic level revealed high concentrations of radioactivity over certain nerve endings, often containing flat vesicles, over glial cells and over neuronal cell bodies probably representing spinal interneurons. Motoneurons, on the other hand, showed only a low activity.     

Synaptic profiles in the outgrowth from chick spinal cord in vitro

Summary Synaptic profiles have been identified in the outgrowth from chick embryo spinal cord maintained in vitro for short periods. Profiles corresponding to types that may be excitatory and inhibitory in the intact central nervous system have been found. Their presence outside expiants, and in occasional relation to glial cells, suggests that neurites themselves may possess a generalised capacity for synapse formation under appropriate circumstances, rather than be limited to specific targets.     

Existence of respiratory interneurons in the cervical spinal cord of the rabbit

A spinal "respiration" generator has been shown to fire phrenic motoneurones in rhythmic bursts. It is very likely driven through bulbo-spinal inspiratory neurones in intact preparations. Although no direct evidence for respiratory interneurones at the C4-C5 spinal levels has been obtained so far (except for Renshaw cells ), it is currently believed that only few inspiratory inputs to the phrenic motoneurones are transmitted monosynaptically from the medulla. We have tried here to record spinal interneuronal respiratory activities in decorticate, unanaesthetized, vagotomized and curarized rabbit preparations. Different functional categories of interneurones could be identified at the C4-C5 spinal levels: inspiratory and expiratory interneurons with various discharge patterns which rather well correspond to the functional categories of inspiratory and expiratory bulbo-spinal neurones described by Bianchi and Richter. In addition, multiunit inspiratory bursting could be followed over several 100 microns during each electrode penetration. The different categories of interneurones were encountered laterally from 700 to 1,000 microns, at depths ranging from 300 to 500 microns dorsally to the phrenic nucleus, down to the nucleus itself. These results indicate that part of the medullary inspiratory drive is channelled via spinal cord interneurones; they also suggest that an inhibition of phrenic motoneurones from the bulbo-spinal expiratory drive takes place via interneurones.     

Synaptic interaction between single motoneurons in the isolated frog spinal cord

The nature of synaptic interaction between two neighboring motoneurons in the isolated frog spinal cord was studied by parallel insertion of two separate micro-electrodes into the cells. In 82 of 89 motoneurons tested transmission through synapses between the motoneurons was electrical in nature, as shown by the absence or short duration of the latent period of elementary intermotoneuronal EPSPs, stability of their amplitude, and preservation of responses in Ca⁺⁺-free solution containing 2 mM Mn⁺⁺. Direct electrotonic interaction was demonstrated in both directions: artificial de- and hyperpolarization of one motoneuron led to corresponding shifts of membrane potential in the neighboring motoneuron. The time constant of rise and decay of this potential was appreciably greater than the time constant of the membrane of the two interconnected motoneurons. Blockade of the SD-component of the action potential in the "triggering" motoneuron led to a decrease in the elementary EPSP in the neighboring motoneuron. These facts suggest that electrotonic interaction takes place through dendro-dendritic junctions. Absence of rectification was demonstrated in electrical synapses between motoneurons. In four cases elementary EPSPs were chemical in nature, for they appeared 1.3–3.3 msec after the beginning of the action potential in the "triggering" motoneuron, and were blocked in Ca⁺⁺-free solution containing Mn⁺⁺; fluctuations of their amplitude approximated closely to a Poisson or binomial distribution. Such responses are evidently generated by synapses formed by recurrent axon collaterals of one motoneuron on the neighboring motoneurons. In three cases elementary intermotoneuronal EPSPs consisted of two components, the first electrical and the second chemical in nature. Morphological structures which may be responsible for generation of 2-component EPSPs are examined.Deceased.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 5, pp. 619–630, September–October, 1984.     

The effect of GABA on lumbar terminations of rubrospinal neurons in the cat spinal cord

Although GABA and piperidine-4-sulphonic acid depolarize I a afferent terminations in the cat spinal cord by activation of bicuculline-sensitive GABA receptors, no evidence was obtained for a bicuculline-sensitive alteration by either gabamimetic of the electrical threshold of rubrospinal terminations in the spinal intermediate nucleus. The terminal axonal arborizations in the spinal cord of neurons in the red nucleus thus do not have GABA receptors similar to those on the cell bodies. The results are discussed in relation to the depolarizing action of GABA on some central neurons, and on neurons with peripheral cell bodies, and to probable differences in the intracellular chloride content of neurons having peripheral or central cell bodies, and thus of different embryological origin. A presynaptic depolarizing inhibitory process mediated by GABA appears to be confined to the terminals of primary afferent fibres in the mammalian central nervous system.     

Connections of the corticospinal and rubrospinal tracts with neurons of the cervical spinal cord in cats

The distribution of focal potentials over the cross section of the 7th cervical segment of the spinal cord was studied during stimulation of the pyramids, the red nucleus, and a peripheral nerve (ulnar) in adult cats anesthetized with chloralose and Nembutal. The earliest focal potentials in the fasciculus dorsolateralis were recorded 1.4–1.5 msec after stimulation of the pyramids and 0.8–0.9 msec after stimulation of the red nucleus. These times correspond to maximal condution velocities of 56–68 and 105–124 m/sec respectively. The earliest post-synaptic activity in response to pyramidal stimulation was found in the lateral areas of laminae V and VI, and in response to stimulation of the red nucleus in laminae VI and VII in Rexed's classification. The pyramidal wave also evoked considerable postsynaptic activity in medial areas of the dorsal horn. In response to stimulation of peripheral afferents activity was evoked in neurons in the central and medial parts of laminae V and VI. It is postulated on the basis of these results that corticospinal and rubrospinal fibers may be connected monosynaptically with specialized interneurons, free from peripheral influences, in the lateral areas of laminae V and VII respectively; in the lateral part of lamina VI convergence of both types of influences on the same cells is possible. Interaction between descending and afferent influences possibly takes place on more medially located neurons.A.A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 158–167, March–April, 1972.