A comparative study of the activity of motoneuron groups of intercostal muscles in cat

The activity of inspiratory and expiratory motor units (MU) has been studied. The statistical data indicate that the recruitment of expiratory motoneurons is slower and more uniform than the recruitment of the inspiratory motoneurons. Most of the expiratory motoneurons showed inhibition shortly before the start of the inspiratory phase. Data are given on other characteristics of the activity and segmental location of both groups of motoneurons. It is postulated that the changes in the MU activity at the beginning and the end of the respiratory period and the coincidence in the extremal activity values of the antagonistic groups are attributable to supraspinal influences.Information Transmission Problems Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 289–295, May–June, 1970.     

Evolution of neuronal systems of suprasegmental motor control

The study of supraspinal systems of motor control in a series of vertebrates by electroanatomical methods shows that certain key features of reticulo-motoneuronal projection persist throughout the scale of evolution from Cyclostomata to primates. There is a particularly marked similarity between the monosynaptic reticulo-motoneuronal EPSPs in primitive animals and in the advanced quadrupeds: amphibians, reptiles, and mammals. Certain general principles governing the maturation of derivatives of the reticulo-spinal system, namely the vestibulo-spinal and rubro-spinal projections, can be discussed. The most marked changes occurred in the development of the mammalian cortico-spinal system. The properties of the conducting system and synaptic connections with the spinal motoneurons differ considerably in the series rodents—carnivores—primates. In this survey the similarities and differences between the pyramidal and nonpyramidal monosynaptic projections to motoneurons in primates and the role of brain-stem structures in the mechanism of cortico-extrapyramidal control are discussed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 453–470, September–October, 1972.     

Correlation between pattern of synaptic effects and direction of changes in RNA content in spinal motoneurons in rats

Spinal motoneurons were activated orthodromically or antidromically with preservation of inhibitory synaptic influences (experiments on healthy rats) and after blocking these influences by tetanus toxin (experiments on rats with local tetanus). The RNA content in the cytoplasm of the -motoneurons was measured by cytospectrophotometry in UV light. The results showed no quantitative changes in the RNA of the motoneurons during action potential generation. Meanwhile the content of neuronal RNA depends on the character of synaptic influences. The RNA content in the motoneurons rises in response to excitatory and falls in response to inhibitory synaptic action. The possible mechanisms of the observed cytochemical changes in the RNA content during synaptic excitation and inhibition of motoneurons are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR. Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 418–422, July–August, 1972.     

Influence of forelimb afferents on the activity of lumbar spinal-cord motoneurons

Experiments were conducted on anesthetized cats with microelectrode recording to study the synaptic responses that develop in the lumbar motoneurons on stimulation of the afferent fibers of groups II and III in the nerves of the ipsilateral and contralateral forelegs. Stimulation of these afferents evoked predominantly inhibitory postsynaptic potentials (IPSP) in the extensor motoneurons and excitatory postsynaptic potentials (EPSP) in the flexor motoneurons. A basically inhibitory change in the rhythmic background activity developed under the influence of descending impulsation. The duration of the total inhibition of "spontaneous" motoneuron activity corresponded to the duration of the inhibitory influences exerted by the forelimb flexor-reflex afferents (FRA) on the interneurons. The interaction of the descending and segmental PSP resulted in inhibition and facilitation of the segmental responses in the motoneurons. The ultimate result of this interaction was determined by the shifts in the membrane potential of the motoneuron and by the effects created in the interneurons.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 58–67, January–February, 1971.     

Investigation of spinal neuronal mechanisms of movement control systems

Morphological and electrophysiological investigations of the means whereby the principal descending motor systems (the cortico-, rubro-, reticulo-, and vestibulo-spinal tracts) are connected with the segmental interneuronal apparatus and motoneurons show that these connections can be based on two different principles. Descending systems either activate motoneurons directly (monosynaptically) or are connected primarily with various interneuron systems, exerting their influence in that case by regulating the activity of simpler or more complex spinal mechanisms. The older descending system (reticulo- and vestibulo-spinal) possess a monosynaptic excitatory action of motoneurons; the evolutionarily newer descending systems, which transmit the most complex motor signals from the cerebral and cerebellar cortex to the spinal cord (cortico- and rubro-spinal), terminate synaptically in every case on interneurons. It is only in primates that a few cortico-spinal fibers form monosynaptic connections with motoneurons. The chief ways of action of the descending systems on interneurons are: control of the afferent inflow into the interneuron system by presynaptic inhibition of the corresponding synapses; control of the interneuron system by postsynaptic interaction with afferent influences; control of motoneurons through the specialized interneuron apparatus. The investigation shows that the last of these mechanisms functions in the cortico- and rubro-spinal, and possibly also in the reticulo- and vestibulo-spinal systems. The functional role of the various means of connection of the descending systems with the spinal neurons in the system of movement control is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 189–202, March–April, 1970.     

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 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.     

Reorganization of the efferent activity of the locomotor generator controlling forelimb movements for electrical stimulation of the descending systems

The reorganization of the parameters of the efferent activity of the forelimb locomotion generator for electrical stimulation of the descending systems is determined in experiments on decerebrate immobilized cats. This generator is found to be characterized by a stable state at which the sum of influences of the signals from different descending systems on the generator is extremely limited. It is concluded that under the influence of these signals, the reorganizations of the activity of the locomotion generators of different limbs bring the motor program into a dynamic (or nearly dynamic) relationship with the supraspinal inflow, allowing for a sufficient limitation and balancing of the influences of the corresponding descending systems on the interneuronal networks determining the temporal and phase characteristics of the activity of these generators.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 704–708, November–December, 1991.     

Cortico-pyramidal and cortico-extrapyramidal synaptic influences on lumbar motoneurons in monkeys

Postsynaptic potentials evoked by stimulation of the motor cortex or pyramids before and after acute pyramidotomy were investigated in the lumbar motoneurons of monkeys. In response to activation of fibers of the pyramidal tract monosynaptic EPSPs predominated in motoneurons innervating the distal muscles of the hind limbs. Monosynaptic EPSPs in the motoneurons of the distal muscles had a significantly higher amplitude and could be evoked by weaker stimuli than EPSPs in the motoneurons of the proximal muscles. Cortico-motoneuronal EPSPs in the motoneurons of the distal muscles had a less marked frequency potentiation than EPSPs with monosynaptic segmental delay in the motoneurons of the proximal muscles. Cortico-extrapyramidal synaptic responses appeared in the pyramidotomized monkeys during intensive repetitive stimulation of the motor cortex in motoneurons of both distal and proximal muscles. These effects, transmitted by descending projections of the brain stem, may be responsible for the partial preservation of cortical motor control after pyramidotomy.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 587–596, November–December, 1972.     

Electrotonic and chemical EPSPs evoked in lamprey motoneurons by descending tract and dorsal root afferent stimulation

Postsynaptic responses evoked by stimulation of the descending tract and dorsal roots were investigated by means of intracellular microelectrodes in experiments on preparation of the isolated lamprey spinal cord. Besides giant reticulospinal (Mullerian) axons, a broad spectrum of descending fibers and dorsal-root afferents were shown to form synaptic inputs with both chemical and electrical mechanisms of transmission with motoneurons, as revealed by the sensitivity of the corresponding PSPs to absence of calcium ions and excess of magnesium ions in the external medium. During combined stimulation electrotonic PSPs may have a rapid temporal course characteristic of elementary responses, but they may also lead to smooth and slow depolarization of the postsynaptic membrane, evidence that they may perform not only a mediator but also an integrative function.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 512–517, September–October, 1977.     

Reticulospinal and propriospinal monosynaptic influences on motoneurons in frogs

Monosynaptic effects evoked by electrical stimulation of suprasegmental structures and the ventral and lateral columns were recorded intracellularly from motoneurons of the lumbar and cervical enlargements after isolation of the spinal cord and medulla in frogs. Reticulospinal fibers arising from cells of the medial reticular formation of the medulla and running in the ventro-lateral columns evoke monosynaptic excitation of cervical and lumbar motoneurons. The reticulo-motoneuronal E PSPs do not exceed 2–3 mV in amplitude and do not reach the threshold for action potential generation. Division of the spinal cord and interaction between all synaptic inputs tested in chronic experiments showed that monosynaptic E PSPs evoked by direct stimulation of the ventral and lateral columns are due to activation of the descending system of propriospinal fibers. By transmembrane polarization experiments the equilibrium potentials of the reticulo-motoneuronal and propriospinal monosynaptic E PSPs could be determined.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 164–173, March–April, 1973.     

Reorganization of spinal segment-to-muscle projections after cross-union of the nerves to hindlimb antagonistic muscles in rats

The nervesn. tibialis comm. andperoneus comm. were transected and cross-united in rats. One and a half, three, or six months later, the parameters of single and tetanic isometric contractions of the musclesm.m. tibialis anterior andtriceps surae evoked by L4 and L5 ventral root stimulations were measured in acute experiments on spinalized animals. In addition, the changes in functional asymmetry of muscle innervation by L4 and L5 motoneurons were studied. The characteristics of them. tibialis comm. andm. triceps surae contractions recovered considerably in three and six months after the nerve cross-union, respectively. In the latter case, the contraction force and preinjury innervational relations recovered to a higher degree than in the former one. Reorganization of segment-to-muscle projections following injury of the peripheral nerves is thought to be one of the neurophysiological mechamisms responsible for compensation of motor disorders. The pattern of this reorganization correlates with initial proportions of motoneuronal axons in different segments sending nerves to the studied muscles, and depends on the level of activity in corresponding motoneurons in natural motor behavior and the intensity of descending influences upon these motoneurons.Neirofiziologiya/Neurophysiology, Vol. 26, No. 3, pp. 163–170, May–June, 1994.     

Synaptic potentials of motoneurons of the masseter muscle

Postsynaptic potentials of 93 motoneurons of the masseter muscle evoked by stimulation of different branches of the trigeminal nerve were studied. Stimulation of the most excitable afferent fibers of the motor nerve of the masseter muscle evoked monosynaptic EPSPs with a latent period of 1.2–2.0 msec, changing into action potentials when the strength of stimulation was increased. A further increase in the strength of stimulation produced an antidromic action potential in the motoneurons with a latent period of 0.9 msec. In some motoneurons polysynaptic EPSPs and action potentials developed following stimulation of the motor nerve to the masseter muscle. The ascending phase of synaptic and antidromic action potentials was subdivided into IS and SD components, while the descending phase ended with definite depolarization and hyperpolarization after-potentials. Stimulation of cutaneous branches of the trigeminal nerve, and also of the motor nerve of the antagonist muscle (digastric) evoked IPSPs with a latent period of 2.7–3.5 msec in motoneurons of the masseter muscle. These results indicate the existence of functional connections between motoneurons of the masseter muscle and its proprioceptive afferent fibers, and also with proprioceptive afferent fibers of the antagonist muscle and cutaneous afferent fibers.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 262–268, November–December, 1969.     

Excitation of accessory motoneurons by stimulation of Deiters' nucleus in the cat

Acute experiments on cats under chloralose-pentobarbital anesthesia showed that application of single stimuli to Deiters' nucleus evoked monosynaptic EPSPs in motoneurons of the accessory nucleus. Latent periods of EPSPs ranged from 1.3 to 2.3 msec (mean 1.8±0.3 msec), their rise time was 0.5–1.0 msec, and their duration 7–10 msec. During repetitive stimulation the EPSPs were weakly potentiated, but with an increase in the strength of stimulation applied to Deiters' nucleus they readily changed into action potentials. In some motoneurons polysynaptic EPSPs with latent periods of the order of 6.0 msec appeared on the descending phase of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 515–519, September–October, 1981.     

Possible organization pattern of interaction between the generators of cyclic motor activity and inputs from supraspinal and afferent systems

Possible organization patterns of scratching and locomotor generators that allow interpretation of experimentally demonstrated reorganizations in temporal parameters of these generator activities after electrical stimulation of descending and peripheral afferent systems were analyzed with application of mathematical simulation of neuronal generator systems. The results obtained led to the conclusion that patterns of such reorganizations influenced by signals from suprasegmental and/or peripheral systems may be determined by only two factors: 1) the structure of synaptic connections between interneuronal functional groups underlying these generator associations, and 2) the structure of connections between these groups of interneurons and fibers from suprasegmental and peripheral afferent sources. The existence of inhibitory-excitatory actions from descending and afferent systems upon the neurons of locomotor or scratching generator half-centers is a sufficient condition to ensure phasic changes in the sensitivity of these generators to supraspinal and afferent signals. The locomotor generator, unlike the scratching generator, is apparently characterized by a more complex organization of connections between functional neuronal groupings and descending fibers.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 45–50, January–February, 1993.     

Synaptic processes in thoracic α-motoneurons evoked by segmental afferent stimulation

Synaptic processes in various functional groups of thoracic motoneurons (Th₉-Th₁₁) evoked by stimulation of segmental nerves were investigated in anesthetized and decerebrate cats. No reciprocal relations were found between these groups of motoneurons. Only excitatory mono- and polysynaptic responses were recorded in the motoneurons of the principal intercostal nerve following stimulation of the homonymous nerve. Activation of the afferents of the external intercostal muscle and dorsal branches does not cause noticeable synaptic processes in these motoneurons; much more rarely it is accompanied by the development of low-amplitude polysynaptic EPSP's. In motoneurons of the dorsal branches, stimulation of homonymous nerves leads to the appearance of simple, short-latent EPSP's. Late responses of the IPSP or EPSP - IPSP type with a predominance of the inhibitory component were observed in most motoneurons of this type following activation of the afferent fibers of the principal intercostal nerve. In other motoneurons of the dorsal muscles, stimulation of the main intercostal nerve (and nerve of the external intercostal muscle) did not evoke apparent synpatic processes. EPSP's (mono- and polysynaptic) appeared in the motoneurons of the external intercostal muscle following stimulation of the homonymous and main intercostal nerves. Activation of the afferents of the dorsal branches was ineffective. The character of the synaptic responses of the respiratory motoneurons to segmental afferent stimulation, investigated under conditions of spontaneous respiration, was different. The characteristics of synaptic activation of thoracic motoneurons by segmental afferents under conditions of hyperventilation apnea and during spontaneous breathing of the animals are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 279–288, May–June, 1970.     

Synaptic mechanisms of the action of subcortical formations on motoneurons in cat facial nerve

Characteristics of the synaptic processes produced by stimulating the head of the caudate nucleus, theglocus pallidus, and the central amygaloid nucleus were investigated in motoneurons of the facial nerve during acute experiments on cats using intracellular recording techniques. It was found that stimulating the first two of these structures causes polysynaptic activation, while both mono- and polysynaptic excitation of facial nerve motoneurons are produced by stimulation of the central amygdaloid nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 800–809, November–December, 1985.     

Factors responsible for multiple discharge of motoneurons in the facial nucleus in cats

The multiple discharge evoked by stimulation of the caudal trigeminal nucleus in motoneurons of the cat facial nucleus was investigated by an intracellular recording method in acute experiments on cats. The multiple discharge was shown to arise on the basis of gradual depolarization of the motoneuron membranes produced as a result of effective summation of high-frequency excitatory influences arriving from the caudal trigeminal nucleus. Factors facilitating the development of this process are the dendritic localization of synaptic endings of projection neurons of the caudal trigeminal nucleus, the dendritic origin of delayed depolarization processes, and the high input resistance of the motoneuron membrane in the facial nerve nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 520–530, September–October, 1981.     

Function of alpha-motoneurons of the human foot muscles in normal conditions and with descending and segmental deprivation

The characteristics of the central response of the abductor hallucis muscle to stimulation of the posterior tibial nerve were studied in healthy subjects and neurological patients. In normal subjects over 22–23 years old the response has the usual properties of a late potential recorded from the small muscles of the foot (F-wave) whereas in children and adolescents it has the features of the central response of a leg muscle. A unilateral lesion of the posterior sacral roots leads to an increase in amplitude and regularity of the F-wave of the foot muscle on the side of the lesion. This is evidence of the antidromic origin of the principle component of the F-wave and points to increased antidromic excitability of the spinal motoneurons in man in the presence of partial segmental deafferentation. A disturbance of descending control, resulting in the loss predominantly of pyramidal influences, is accompanied by regeneration of the characteristic features of the late potential found in responses recorded in adolescent subjects. The same phenomenon can also be observed in pathology of the posterior horns of the cervical portion of the spinal cord when no pyramidal disorders can be detected clinically. The central response is much less frequently changed in lesions of the ventral structures of higher segments. The significance of descending control for establishment of the level of excitability in the population of motoneurons innervating the muscles of the human foot is discussed.O. V. Kuusinen Petrozavodsk State University. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 563–570, November–December, 1973.     

Synaptic processes evoked by intracortical microstimulation in lumbar motoneurons of rats

Experiments with intracortical microstimulation and intracellular recording from motoneurons of the rat hind limb showed that synaptic effects due to activation of pyramidal neurons of the motor cortex and transmitted along the pyramidal tract are exclusively polysynaptic in character. Mainly excitatory effects were found in motoneurons of flexors and extensors, and of distal and proximal muscles. The minimal intensity of intracortical stimulation required for synaptic excitation of -motoneurons is 5–10 µA. Low-threshold synaptic effects in lumbar motoneurons and movements of the hind limbs are evoked from the same zones.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 174–180, March–April, 1973.