Interaction between segmental and descending intersegmental reflexes in lumbar motoneurons

The effects of segmental reflexes on descending intersegmental reflexes to stimulation of forelimb afferents were studied in anesthetized cats by recording postsynaptic responses from single motoneurons. Interaction between these influences was found to be reciprocal in character for groups of neurons with primary connections with afferents of the superficial and deep branches of the peroneal nerve and afferents of the nerve to the gastrocnemius muscle. Excitatory postsynaptic responses arising in groups of motoneurons of the peroneal nerve to stimulation of forelimb afferents underwent profound and prolonged inhibition during conditioning stimulation of afferents in the deep and superficial peroneal nerves. Activation of segmental afferents during conditioning stimulation of the gastrocnemius nerve was accompanied by inhibition of excitatory intersegmental responses and deinhibition of inhibitory responses in motoneurons of the gastrocnemius muscle. Segmental inhibition of intersegmental descending impulse activity appeared in the interneuron system of the segmental reflex centers connecting the descending propriospinal tracts with the motoneurons of these centers.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 16872-175, March–April, 1972.     

Activity of lumbar interneurons during late long-lasting discharges in motor nerves of immobilized thalamic cats

Activity of lumbar spinal neurons was recorded extracellularly during late long-lasting discharges in efferent nerves in immobilized thalamic cats. Of the total number of cells tested, 70% changed their activity during late discharges. The activity of 35% of neurons was increased during late discharges in nerves to flexors, but inhibited during discharges in nerves to extensors. Responses of 27% of neurons were of the opposite character. Other neurons were found whose activity was increased (5%) and reduced (3%), respectively, during later discharges in both flexor and extensor nerves. Most interneurons which changed their activity during late discharges were located in lateral parts of the intermediate zone of gray matter and the ventral horn at a depth of 2.8 mm. The character of the afferent input to a neuron was found to depend on the late efferent discharges and activity of the neurons correlated with them. Neurons whose activity was unchanged during late discharges (30%) were mainly located rather more dorsally, at a depth of about 2.0 mm. The possible mechanisms of the participation of these groups of interneurons in the generation of late discharges are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 236–244, May–June, 1979.     

Reorganization of segmental responses to peripheral stimulation during fictitious scratching in cats

Segmental reflex responses of the lumbosacral region of the spinal cord to stimulation of peripheral afferents were studied in immobilized decerebrate cats before and after application of D-tubocurarine or bicuculline to the superior cervical segments, potentiating the scratch reflex, and also during fictitious scratching evoked by mechanical stimulation of the ear. Application of these substances led to inhibition of the N₁-component of the dorsal cord potential, the dorsal root potential, and polysynaptic responses in efferent nerves. The appearance of fictitious scratching was accompanied by additional tonic inhibition of these responses, against the background of which modulation of the amplitudes of the responses was observed depending on the phase of fictitious scratching. Modulation of amplitudes of monosynaptic reflexes also developed during fictitious scratching. Against the background of these results the mechanisms and physiological role of reorganization of segmental responses during activation of the spinal scratching generator are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 196–203, March–April, 1981.     

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 162–172, March–April, 1978.     

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.     

Presynaptic mechanisms of changes in segmental responses accompanying the formation of a spinal locomotor generator in the cat

Using unanesthetized and decorticated (or decerebrated at level A 13) cats, it was found that spinalization leads to depolarization of the central terminals of primary afferents and an increase in the N₁ component of dorsal surface potential and dorsal root potential (DRP) produced by stimulating the low-threshold cutaneous and muscle afferents. Other effects include an increase in early polysynaptic responses and DRP produced by stimulation of high-threshold muscle afferents, a reduction in the intensity of interneuron activation in the nucleus interpositus mono- and polysynaptically connected with primary afferents, and a rise in the activity of n. interpositus interneurons di- and oligo-synaptically connected with afferent terminals. Changes in the opposite direction were produced by injecting DOPA into spinal animals. The connection between changes in the state of the segmental neuronal apparatus of the lumbosacral spinal cord and the level of spinal locomotor generator activity is discussed in the light of the findings obtained.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 669–678, September–October, 1986.     

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.     

Respiratory modulation of the startle reflex in cats

Phase respiratory influences on reflex after-discharges in response to stimulation of the segmental nerves as well as tactile and acoustic stimulation in the limb and intercostal nerves — physiological analogs of startle reflexes (SR) were studied in unanesthetized (decerebrate) or chloralose-anesthetized cats. It was found that the level of these reflexes in the inhalation phase of respiration was 8–58% lower than during exhalation. The difference between the inhalation and exhalation phases was determined for different types of reflexes and under varying experimental conditions. Evidence was obtained that respiratory modulation of reflexes occurs mainly at the level of suprasegmental (reticular) mechanisms. Clear distinctions could be drawn between the pattern of reflex modulation in the lower intercostal nerves and those of the limbs. Findings would lead to the conclusion that the likely mechanisms underlying suprasegmental respiratory influences on these reflexes differ, as does the organization of their reticular centers.S. V. Kurashov Medical Institute, Ministry of Public Health of the RSFSR, Kazan'. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 593–603, September–October, 1986.     

Depolarization of primary afferents during fictitious scratching in thalamic cats

The dorsal cord and dorsal root potentials were recorded in immobilized thalamic cats during fictitious scratching evoked by mechanical stimulation of the ear. Depolarization of primary afferents was shown to be simulated by the central scratching generator. Antidromic spike discharges appeared at the peak of the primary afferent depolarization waves in certain afferent fibers. Similar discharges arise in the resting state in response to stimulation of limb mechanoreceptors. It is suggested that during real scratching primary afferent depolarization and antidromic spikes evoked by it may effectively modulate the level of the afferent flow to spinal neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 173–176, March–April, 1978.     

Efferent activity in the phrenic nerve during startle reflex in chloralose anesthetized cats

Efferent activity was investigated in the phrenic nerve during startle reflex manifesting as somatic nerve discharges (lower intercostal nerves and the nerve endings) in chloralose anesthetized cats. Inhibition (usually of short duration, lasting 23–36 msec) of inspiration activity was found to be the main component of response in the phrenic nerve in the shaping of "low threshold" startle reflex produced by acoustic and tactile stimuli and stimulation of low threshold peripheral afferents. Reflex discharge prevailed amongst the response patterns produced in the phrenic nerve by stimulating high threshold afferents, i.e., early (propriospinal) and late (suprasegmental, arising from stimulating intercostal nerve) or late only (when stimulating the hindlimb nerves). Two patterns of late response could be distinguished, one on inspiration (found in roughly 3 out of 4 experiments) and other on exhalation — the respiratory homologs of somatic startle reflex. Response pattern is described throughout the respiratory cycle. Structure and respiratory modulation of reflex responses produced in the phrenic nerve by stimulating bulbar respiratory structure are also examined. Possible neurophysiological mechanisms underlying phrenic response during the shaping of startle reflex are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 473–482, July–August, 1987.     

Action of ammonium acetate on central primary afferent depolarization

Experiments on anesthetized spinal cats showed that ammonium acetate, injected intravenously (2–4 mmoles/kg) inhibits the depolarization of the central endings of primary afferent fibers activated by stimulation of afferent nerves. Inhibition of primary afferent depolarization is transient in character and develops parallel with depression of postsynaptic inhibition of monosynaptic reflexes. The depression produced by the action of ammonium was not due to blocking of negative postsynaptic potentials of the dorsal surface of the spinal cord or blocking of reflex electrical discharges in the ventral spinal roots. It is suggested that depression of primary afferent depolarization is due to a decrease in the emf for synaptic ion currents producing depolarization.Allergologic Research Laboratory, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 52–60, January–February, 1977.     

Changes in antidromic discharges in peripheral nerves during polarization of the cat spinal cord by a steady current

The effect of a steady current passed through the spinal cord on antidromic discharges in primary afferent groups of Agb cutaneous nerves of the hind limb, evoked by single and paired stimulation of the terminals of these fibers, was investigated by Wall's technique in acute experiments on spinal and anesthetized cats. A current of up to 50–100 µA, flowing in the dorso-ventral direction, led to an increase in amplitude of antidromic dischanges evoked by single stimulation of afferent terminals; if the current flowed in the opposite direction, the opposite effect was observed. The relative degree of facilitation of antidromic discharges caused by conditioning stimulation of these same fibers was reduced by a polarizing current in either direction. It is suggested that the effects of the action of a steady current flowing through the spinal cord observed in these experiments are due mainly to shifts of membrane potential in primary afferent terminals.Dnepropetrovskii State University. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 386–391, July–August, 1982.     

Inhibition of jaw opening reflexes by stimulation of the central gray matter and raphe nuclei in cats

The effect of stimulation of the mesencephalic central gray matter and raphe nuclei on jaw opening reflexes evoked by excitation of high-threshold (dental pulp) and low-threshold (A-alpha) fibers of the infraorbital nerve afferents was studied in cats anesthetized with chloralose and pentobarbital. The jaw opening reflex evoked by stimulation of the dental pulp was shown to be effectively suppressed by conditioning stimulation of the central gray matter and raphe nuclei. The reflex evoked by stimulation of low-threshold infraorbital nerve afferents also was depressed (but less deeply and for a shorter period than the reflex evoked by stimulation of the dental pulp) during stimulation of the raphe nuclei and caudal zone of the central gray matter, but was unchanged after stimulation of the points located in the rostral zone of the central gray matter. Application of single stimuli or bursts of five stimuli with a frequency of 100 Hz had no effect on the reflexes studied. Short-term stimulation with a burst of 10–20 stimuli with a following frequency of 200–400 Hz led to inhibition of the reflexes, which lasted 450–1000 msec. Long-term stimulation of the central gray matter and raphe nuclei for 30 sec with a frequency of 50 Hz caused inhibition of jaw opening reflexes evoked by stimulation of both high- and low-threshold afferents for 60 min. Impulses from the central gray matter and raphe nuclei thus have a mainly inhibitory action on the jaw opening reflex evoked by stimulation of high-threshold afferents, but they act less effectively on the reflex evoked by stimulation of low-thres-hold afferents. The duration of inhibition depends essentially on the parameters of stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 374–387, May–June, 1984.     

Effect of substances potentiating or inhibiting unit activity in the locus coeruleus on some types of spinal inhibition in cats

Microinjections of aspartic acid and chlorpromazine into the region of the locus coeruleus, which strengthen spontaneous unit activity in that structure, in decerebellate cats anesthetized with chloralose, led to depression of the inhibitory influence of flexor reflex afferents on extensor discharges, but did not change the facilitatory action of these afferents on flexor monosynaptic discharges and had no effect on recurrent inhibition of extensor discharges or reduced it. Microinjection of noradrenalin into this region, which depresses spontaneous unit activity in the locus coeruleus, or of procaine, which blocks action potential generation in neurons, led to potentiation of the inhibitory action of flexor reflex afferents on extensor discharges and to strengthening of recurrent inhibition, but did not affect the facilitatory action of these afferents on flexor discharges. The role of tonic descending influences of the locus coeruleus in the control of spinal inhibition evoked by flexor reflex afferents is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 247–256, May–June, 1981.     

Contribution of homosynaptic depression to stabilization of spinal cord potentials

The following were measured during experiments on spinal anesthetized cats: firstly, variations in the amplitude of dorsal root potentials produced by applying single or regular stimuli in 120–150 trails to hindlimb cutaneous nerves and dorsal surface of the spinal cord and secondly, numbers of extracellular discharges in neurons involved in generating these potentials. A reduction in the variation between these parameters was found when applying stimulation at the rate of 0.1–5.0 Hz. The authors attribute the effect observed to the influence of homosynaptic depression.Institute of Biology, State University Commemorating 300th Anniversary of Russian-Ukrainian Reunion, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 180–185, March–April, 1988.     

Reticular structures and reticulospinal pathways participating in the initiation and inhibition of spino-bulbo-spinal activity

Reflex discharges in intercostal nerves and activity of reticulospinal fibers of the ventral and lateral funiculi, evoked by stimulation of the reticular formation and of the splanchnic and intercostal nerves were investigated in cats anesthetized with chloralose (50 mg/kg). Brain-stem neuronal structures participating in the "relaying" of spino-bulbo-spinal activity were shown to lie both in the medial zones of the medullary and pontine reticular formation and in its more lateral regions; they include reticulospinal neurons and also neurons with no projection into the spinal cord. Structures whose stimulation led to prolonged (300–800 msec) inhibition of reflex spino-bulbo-spinal activity were widely represented in the brain stem, especially in the pons. Analogous inhibition of this activity was observed during conditioning stimulation of the nerves. Reticulospinal fibers of the ventral (conduction velocity 16–120 m/sec) and lateral (17–100 m/sec) funiculi were shown to be able to participate in the conduction of spino-bulbo-spinal activity to spinal neurons. In the first case fibers with conduction velocities of 40–120 m/sec were evidently most effective. Evidence was obtained that prolonged inhibition of this activity can take place at the supraspinal level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 373–383, July–August, 1976.     

Peculiarities of the synaptic adaptation of the intermediate neurons of the thoracic segments of the spinal cord by cutaneous,muscle, and visceral afferents

The responses of the interneurons of the thoracic segments of the spinal cord to stimulation of the intercostal and splanchnic nerves were studied on decerebrated and narcotized cats. It was established that the neurons of different layers of the gray matter (according to Rexed) differ substantially in type of afferent inputs. Cells in laminae I–III and IV are activated chiefly by somatic afferents: primarily high-threshold in laminae I–III and low-threshold in lamina IV. The neurons of lamina V and most of the neurons of laminae VII and VIII respond to stimulation of high-threshold somatic afferents (cutaneous fibers of the A group and muscle afferents of groups II and III), as well as visceral afferents of group A, conducting impulses at a rate of 9–35 m/sec. Cells of laminae VII and VIII, monosynaptically activated by muscle afferents of group I, do not respond to stimulation of the visceral afferents. The peculiarities of the "functional" laminar organization of the thoracic segments of the spinal cord are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 563–572, November–December, 1970.     

Effect of noradrenalin and serotonin on synaptic transmission in the rat spinal cord

Experiments on superfused isolated spinal cord preparations from rats aged 8–13 days showed that noradrenal in and serotonin have only a weak effect on monosynaptic reflex discharges but a substantial effect on polysynaptic motoneuronal discharges: noradrenalin potentiates whereas serotonin inhibits them. Both amines inhibit dorsal root potentials evoked by stimulation of high-threshold afferents. Potentiation of polysynaptic motoneuronal discharges induced by noradrenalin is connected with hyperpolarization of high-threshold afferents due to inhibition of the function of neurons in the substantia gelatinosa, and with increased excitability of interneurons participating in the generation of motoneuronal discharges. Serotonin inhibits polysynaptic motoneuronal discharges through its direct depolarizing effect on terminals of high-threshold afferents and depression of interneuron activity responsible for these discharges. Adrenergic and serotonin receptors, mediating these effects of noradrenalin and serotonin, were subjected to pharmacologic analysis.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 241–247, May–June, 1982.     

Effects of peripheral inputs from hindlimb on the monosynaptic reflex of motoneurons innervating tail muscles.

The effects of group II muscle (PBSt, GS) and cutaneous afferent (Sur, SPc, Tib) inputs from the hindlimb on the monosynaptic reflexes of motoneurons innervating tail muscles were studied in lower spinalized cats. Stimulation of the cutaneous nerves at the conditioning-test stimulus interval of about 10-20 ms facilitated and inhibited the monosynaptic reflexes of ipsilateral and contralateral tail muscles, respectively. The effects of the muscle nerve stimulation were not so prominent as those elicited by cutaneous nerve stimulation. The monosynaptic reflex was also inhibited by muscle nerve stimulation at 10-50 ms intervals. The effects of conditioning stimulation of the hindlimb peripheral nerves at short intervals were depressed or blocked by section of the ipsilateral lateral funiculus at S1 spinal segment. These findings show that the neuronal pathway from hindlimb afferents to tail muscle motoneurons passed the lateral funiculus of the spinal cord and modulates the motoneuronal activity of tail muscles.     

Altered excitability of and synaptic effects of motoneurons during the establishing of a locomotor generation in the cat

Research was performed on spinal cats injected with DOPA and decorticate (decerebrated at level A 13) and spinal cats. It was found that formation (activation) of the spinal locomotor generator is accompanied by heightened excitability in the extensor and the reverse trend in the flexor motoneurons, by an increase in the efficacy of recurrent and reciprocal Ia inhibition of -motoneurons, and by a weakening of the influence of Ib afferents and extensor reflex afferents on these same motoneurons. The likely functional role of these changes in tuning of the spinal segmental apparatus in the generation of locomotor rhythm is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 679–687, September–October, 1986.