Transmission of descending activity evoked by prolonged stimulation of the pyramids and red nucleus by groups of spinal interneurons

Responses of two groups of spinal interneurons to prolonged stimulation of the medullary pyramids and the red nucleus by repetitive and random sequences of stimuli were investigated in cats anesthetized with pentobarbital. Interneurons specialized for transmission of descending, but not peripheral, effects were excited by impulses from both higher structures; the evoked activity was stable and stationary in character in response to stimulation within the range from 20–30 to 75–100/sec. The response of interneurons activated by flexor reflex afferents was more complex and, as a rule, it was not stationary. Prolonged pyramidal stimulation led to an increase in the mean spontaneous firing rate, while stimulation of the red nucleus inhibited spontaneous activity. Statistical analysis of the records of unit activity on the "Dnepr'-1" computer was used to study some possible mechanisms of the transformation of activity in the lateral descending systems by these groups of interneurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 644–653, November–December, 1973.     

Serotonin-induced changes in the action of functionally distinct neurons in Helix pomatia

The effects of serotonin on the amplitude of summated EPSP in interneurons and on the duration of action potentials in sensory neurons, interneurons, and motoneurons involved in avoidance behavior were investigated in functionally distinct neurons isolated from theHelix pomatia nervous system. The duration of action potentials in sensory neurons was found to increase under the effects of serotonin (and this could underly the rise in EPSP amplitude), although that of interneuron and motoneuron spikes did not change. The functional significance of selective neuronal response to a rise in serotonin concentration is discussed, together with the mechanics underlying such effects.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 316–322, May–June, 1987.     

Presynaptic mechanisms for intensifying reactivity of command neurons in Helix pomatia defensive behavior under the effects of vasopressin analog

This study set out to investigate presynaptic mechanisms underlying reactivity of command neurons inHelix pomatia defensive behavior under the effects of desglycine-arginine vasopressin, a vasopressin analog. Peptide perfusion was found to intensify accumulated EPSP in command neurons during stimulation of the nerve without affecting the monosynaptic connection between primary sensory and command neurons. It was concluded that parallel pathways exist for the spread of excitation from the periphery to command neurons. Properties of such pathways are described and neurons with similar properties are identified. It is in these same cells that long-term changes in spontaneous EPSP induced by application of the peptide were noted.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 723–730, November–December, 1990.     

Electrophysiological investigation of nonpyramidal neurons of the radial layer in guinea pig hippocampal slices

The activity of 67 nonpyramidal neurons from the str. radiatum moleculare (NSRM) and 8 presumed interneurons of str. orienspyramidale (NSOP) was recorded in guinea pig hippocampal slices. In contrast with the high frequency grouped discharges characteristic of NSOP, NSRM had low frequency background activity consisting of a single action potential (77%) and grouped spikes (23%). The spontaneous firing rate of neurons of the radial layer decreased with increasing distance from the pyramidal layer. NSRM responded with one or two action potentials rather than a burst of spikes to electrical stimulation of the dentate fascia. The threshold of response for NOSP was lower, while that of NSRM was the same on average but was significantly higher than for NSOP on a number of occasions. The response of both types of neuron was usually accompanied by an inhibitory pause. During induced epileptoid activity single or grouped discharges arose in neurons of both types concurrently with synchronized bursts in the pyramidal cells. It is postulated that NSOP exert an excitatory effect on NSRM.Institute of Biophysics, Academy of Sciences of the USSR, Puschino-on-Oka, Moscow Province, Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 99–108, January–February, 1986.     

Reticulofugal influences of interneurons in the lateral region of gray matter of the cat spinal cord

Responses of lumbar interneurons located in the most lateral regions of Rexed's laminae IV–VII to stimulation of the medial longitudinal bundle and gigantocellular reticular nucleus of medullary pyramids, red nucleus, and peripheral nerves were investigated in cats anesthetized with pentobarbital. Stimulation of the reticulospinal fibers evoked monosynaptic excitation of many interneurons specialized for transmitting activity of the lateral descending systems, but not of peripheral afferents. Convergence of excitatory influences of all three descending systems (cortico-, rubro-, and reticulospinal) was observed on some cells of this group. In addition, monosynaptic "reticular" E PSPs appeared in interneurons transmitting activity of group Ia muscle fibers and in some interneurons of the flexor reflex afferent system. Stimulation of reticulospinal fibers evoked IPSPs in some neurons of this last group. Neurons not exposed to reticulofugal influences (both specialized neurons and interneurons of segmental reflex arcs) were located chiefly in the dorsal zones of the region studied. Recordings were also obtained from single fibers of the lateral reticulospinal tracts (conduction velocity from 26 to 81 m/sec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 525–536, September–October, 1973.     

After-effects of repetitive stimulation in spinal neurons

Spontaneous activity of interneurons before and after repetitive stimulation at 0.1–0.5/sec was recorded in acute experiments on spinal cats and kittens. Using the dynamic selective correlation method a search was made for areas of spontaneous activity with the same distribution of action potentials in time as in the averaged evoked response to a single stimulus. In the case of some neurons portions of the background which correlate reliably in structure with the evoked response repeated at an interval equal to or a multiple of the interval of stimulation. Reproduction of the rhythm of stimulation in the spontaneous activity is intensified with an increase in the total duration of preceding stimulation with the same input and shows positive correlation with the degree of posttetanic potentiation. The facts obtained are evidence of prolonged after-processes in spinal neurons.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 272–280, May–June, 1973.     

Analysis of activity of neuron pairs in the cat caudate nucleus

Activity of neuron pairs in the caudate nucleus, derived simultaneously by a single microelectrode, was investigated in experiments on lightly anesthetized, immobilized cats. Strong temporal correlation was shown to be characteristic of the spontaneous activity of a neuron pair if grouped discharges were present in that activity. If, however, spontaneous activity was characterized by impulses randomly distributed in time, temporal correlation was observed in only 50% of cases, it was weaker, and it reflected excitatory and inhibitory interactions equally. In many cases negative correlation was observed in discharges of neurons within the time interval of 0–4 msec. Electrical stimulation of the various afferent inputs of the caudate nucleus not only did not cause correlation to appear in the discharges of the neurons but, on the contrary, it abolished correlation which existed for that same pair of neurons discharging spontaneously. Comparison of the results with data in the literature indicates that, by the character of interaction of its neurons, the caudate nucleus is one of the group of associative nuclei of the brain.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 486–493, September–October, 1978.     

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.     

Responses of cat pulvinar neurons to moving visual stimuli

Responses of 114 pulvinar neurons to moving visual stimuli were studied. Most (79) neurons possessed spontaneous activity (10–25 spikes/sec). Of 59 neurons tested, 31 responded to stimulation of both retinas and 28 to stimulation only of the contralateral retina. Of 114 neurons, 41 responded only to movement of black objects, while the rest responded to movement of both black and light objects. According to the character of their responses to movement the neurons were divided into two main groups. The first group consisted of neurons sensitive to the direction of motion and responding with a spike discharge to movement in one direction and by inhibition to movement in the opposite direction. The second group included neurons insensitive to the direction of motion and responding by an equal number of discharges to movements in two opposite directions. Besides these two main groups, other neurons responding to movement in two opposite directions by discharges with different temporal distribution and also neurons which changed the character of their response from nondirectional to directional depending on the size of the moving stimulus, were found.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 348–354, July–August, 1978.     

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.     

Nonolfactory afferent telencephalic projections in frogs

The degree of modal specificity of neurons of the tectum, dorsal thalamus, and primordial hippocampus relative to visual (photic) and somatic (tactile) stimulation was investigated in experiments on frogs (Rana temporaria) immobilized with tubocurarine. The specificity of sensory information arriving at the successive levels of the frog's thalamo-telencephalic afferent system diminishes in an ascending direction. Evoked potentials arising in the telencephalon in response to electrical stimulation of the sciatic nerve and to flashes are found not only in the primordial hippocampus, but also bilaterally in the septum and striatum. It is concluded on the basis of discharges recorded in the fibers of the thalamo-telencephalic tracts during somatic and visual stimulation that fibers carrying nonolfactory information into the telencephalon run in the medial and lateral forebrain bundles.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. International Brain Research Laboratory, Kotor, Yugoslavia. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 537–544, September–October, 1973.     

Pyramidal influences on interneurons of spinal segmentary reflector arcs in cat

Microelectrode discharges of potentials have been realized from segmentary interneurons of the dorsal horn and intermediate nucleus of the spinal cord in cat at the L₆–L₇ level by electrical stimulation of the sensorimotor region of the brain cortex. It has been established that corticifugal influences on segmentary interneurons of the system of the flexor reflex and on neurons activated by high threshold muscle afferents (groups Ib, II, and III), or high threshold cutaneous afferents are predominantly excitatory. Interneurons activated by muscle afferents of group Ia or by the lowest threshold cutaneous fibers are weakly subjected to pyramidal influences. The mean latencies of excitatory postsynaptic potentials (EPSP's) and discharges evoked under the influence of pyramidal volley, for the neurons under study in the system of afferents of the flexor reflex are equal to 11.8±2.6 and 20.1±1.8 msec, respectively; for interneurons, excited only by high threshold muscle afferents, they are equal to 15.5±3.6 and 16.3±2.2 msec, respectively; and for interneurons, excited by high threshold cutaneous fibers they are equal to 11.8±2.6 and 18.3±1.4 msec, respectively. Possible pathways of activating segmentary interneurons from the lateral sensorimotor region of the brain cortex have been discussed.The A. A. Bogomolets Institute of Physiology, Academy of Sciences, Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 17–25, January–February, 1970.     

Mechanisms of interaction between central neurons and abdominal stretch receptors in the crayfish

Mechanisms of interaction between central and receptor neurons of the crayfish (the principal inhibitory neuron — PIN — and the slow-adapting stretch receptor — SAR) when functioning under different conditions were investigated: during regular spontaneous activity of SAR, grouped discharges of PIN, and regular spontaneous activity of PIN. A close connection was found between the various parameters of the PIN and SAR responses. Adaptation of SAR to the action of adequate, regular repetitive stimulation takes place faster in the presence of stationary background activity of PIN. The appearance and disappearance of SAR spike activity are determined by the ratio between the firing rates of SAR and PIN: at the moment of changeover the neuron with the higher firing rate is predominant.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Institute of Zoology, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 429–438, July–August, 1972.     

Unit activity in the superior colliculus after removal of corticofugal control

Changes in spontaneous and evoked unit activity in the superior colliculus of the cat were studied after unilateral blocking of corticofugal connections. Functional characteristics of the cells were compared in the intact and disconnected colliculus. In neurons on the side of the operation the spontaneous firing rate was reduced and responses to photic stimulation were virtually completely abolished: only 7.1% of collicular cells on the side of the operation responded to adequate stimulation. Effective mechanisms of corticofugal control, modulating the relaying of the efferent volley in the tectal neurons, evidently function in the superior colliculus.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 54–61, January–February, 1978.     

Synaptic activation of thoracic interneurons by reticulospinal fibers of the lateral funiculus

Synaptic responses of different functional groups of interneurons in segments T10 and T11 to stimulation of the ipsilateral and contralateral medullary reticular formation were investigated in anesthetized cats with only the ipsilateral lateral funiculus remaining intact. Activation of reticulospinal fibers of the lateral funiculus with conduction velocities of 30–100 m/sec was shown to induce short-latency and, in particular, monosynptic EPSPs in all types of cells tested: in interneurons excited by group Ia muscle afferents, in cells activated only by high-threshold cutaneous and muscle afferents (afferents of the flexor reflex), in cells activated mainly by descending systems, and, to a lesser degree, in neurons connected with low-threshold cutaneous afferents. These cell populations are located mainly in the central and lateral parts of Rexed's lamina VII. Most neurons in laminae I–V of the dorsal horn, except six cells located in the superficial layers of the dorsal horn, received no reticulofugal influences. The functional organization of connections of the lateral reticulospinal tract with spinal neurons is discussed and compared with the analogous organization of the medial reticulospinal tract, and also of the "lateral" (cortico- and rubrospinal) descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 150–161, March–April, 1978.     

Interaction between excitation and inhibition in presumptive hippocampal inhibitory interneurons

Electrical responses of 25 presumptive hippocampal inhibitory interneurons to stimulation of two afferent systems of fibers, originating in the contralateral hippocampus, were investigated in acute experiments on unanesthetized, immobilized rabbits. Inhibitory neurons were found to have a relatively ineffective inhibitory input as well as a very effective excitatory input. On interaction between synaptic processes during spontaneous and evoked activity the excitatory input clearly predominates over the inhibitory and plays a definite role in behavior of the neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 580–587, November–December, 1980.     

Functional properties of interneurons of the masticatory reflex

Interneurons of the supratrigeminal nucleus, transmitting effects from the sensory and motor branches of the trigeminal nerve to motoneurons of the muscles of mastication were investigated. Two groups of interneurons with different functional connections were found. The first group (A) contains neurons excited during stimulation of the sensory branches and the motor nerve to the digastric muscle (A₁), neurons excited during stimulation of sensory branches and high-threshold afferents of the motor nerve to the masseter muscle (A₂), and neurons excited only by low-threshold afferents of the motor nerve to the masseter muscle (A₃). Neurons of the second group (B) were activated only by sensory fibers of the trigeminal nerve. It is postulated that interneurons of group A transmit inhibitory effects to motoneurons of antagonist muscles of the lower jaw. Group B interneurons participate in the transmission of excitatory influences to motoneurons of the digastric muscle.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 150–157, March–April, 1972.     

A study of single sympathetic preganglionic neurons in the lateral horns of the lumbar spinal cord

Antidromic discharges and spontaneous activity of single sympathetic preganglionic neurons in the lateral horns of the second lumbar segment of the spinal cord were recorded extracellularly in cats anesthetized with a mixture of chloralose and pentobarbital. A new technique used to identify antidromic discharges of sympathetic preganglionic neurons is described and the characteristics of discharges and sites where they were recorded are investigated. Changes in the frequency of spontaneous discharges of most neurons were shown to be connected with different types of fluctuation of the arterial pressure. Absence of functional specialization of the sympathetic preganglionic neurons is postulated.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.3, pp.295–303, May–June, 1974.     

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.     

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.