Characteristics of unit responses of the cat cerebellar cortex to acoustic stimuli

Investigation of unit responses of the cerebellar cortex (lobules VI–VII of the vermis) to acoustic stimulation showed that the great majority of neurons responded by a discharge of one spike or a group of spikes with a latent period of 10–40 msec and with a low fluctuation value. Neurons identified as Purkinje cells responded to sound either by inhibition of spontaneous activity or by a "climbing fiber response" with a latent period of 40–60 msec and with a high fluctuation value. In 4 of 80 neurons a prolonged (lasting about 1 sec or more), variable response with a latent period of 225–580 msec was observed. The minimal thresholds of unit responses to acoustic stimuli were distributed within the range from –7 to 77 dB, with a mode from 20 to 50 dB. All the characteristics of the cerebellar unit responses studied were independent of the intensity, duration, and frequency of the sound, like neurons of short-latency type in the inferior colliculi. In certain properties — firing pattern, latent period, and threshold of response — the cerebellar neurons resemble neurons of higher levels of the auditory system: the medial geniculate body and auditory cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 3–12, January–February, 1973.     

Responses of medial geniculate body neurons to auditory cortical stimulation

Extracellular and intracellular unit responses of thepars principalis of the medial geniculate body to stimulation of the first (AI), second (AII), and third (AIII) auditory cortical areas were studied in cats immobilized with D-tubocurarine. In response to auditory cortical stimulation both antidromic (45–50%) and orthodromic (50–55%) responses occurred in the geniculate neurons. The latent period of the antidromic responses was 0.3–2.5 msec and of the orthodromic 2.0–18.0 msec. Late responses had a latent period of 30–200 msec. Of all neurons responding antidromically to stimulation of AII, 63% responded antidromically to stimulation of AI also, confirming the hypothesis that many of the same neurons of the medial geniculate body have projections into both auditory areas. Orthodromic responses of geniculate neurons consisted either of 1 or 2 spikes or of volleys of 8–12 spikes with a frequency of 300–600/sec. It is suggested that the volleys of spikes were discharges of inhibitory neurons. Intracellular responses were recorded in the form of antidromic spikes, EPSPs, EPSP-spike, EPSP-spike-IPSP, EPSP-IPSP, and primary IPSP. Over 50% of primary IPSP had a latent period of 2.0–4.0 msec. It is suggested that they arose through the participation of inhibitory interneurons located in the medial geniculate body.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 5–12, January–February, 1976.     

Microelectrophoretic study of unit responses of the rabbit amygdaloid nucleus to acetylcholine and noradrenaline

Responses of 152 neurons of the basal and lateral nuclei of the amygdala and of the anterior amygdaloid field to microelectrophoretic application of acetylcholine and noradrenalin, in the case of 115 neurons to both substances, were investigated in immobilized, unanesthetized rabbit. In the basal nucleus 35% of neurons tested responded to acetylcholine, most often by an increase in discharge frequency (34%), and 63% of cells responded to noradrenalin, most of them giving inhibitory responses (53%). A response to only one of the two substances applied in turn was given by 45% of neurons. Among neurons responding to both acetylcholine and noradrenalin, 23% of cells did so in the opposite direction and only 11% in the same direction.     

Effect of vasopressin and oxytocin on spontaneous unit activity of dorsal horn cells in the isolated spinal cord of young rats

The effect of vasopressin and oxytocin, added to the perfusion solution, on the spontaneous firing rate of single dorsal horn cells was studied in experiments on an isolated segment of spinal cord from rats aged 2–3 weeks. Both neuropeptides were found to have a mainly inhibitory action. Under the influence of vasopressin the spontaneous firing rate of 74% of cells (29 of 39 cells responding to vasopressin) fell, and only in 26% (10 of 39 cells) did it rise. Oxytocin inhibited spontaneous activity of 67% of cells (14 of 21 which responded) and excited 33% of neurons (seven of 21). The effects were dose-dependent and reversible. The cells either responded in the same way to vasopressin and oxytocin or they responded to application of one peptide but not of the other.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 314–320, May–June, 1985.     

Role of the midbrain periaqueductal gray matter in conditioned reflexes

Unit activity in the midbrain periaqueductal gray matter (PGM) during an instrumental placing reflex, its extinction, differentiation, and conditioned inhibition, was studied in chronic experiments on cats. Spike responses 1–2 sec in duration in 69 (36.7%) of 182 neurons preceded by 400–800 msec the beginning of conditioned-reflex and voluntary intertrial movements. These advanced responses appeared 200 msec before the corresponding advance responses of motor cortical neurons. Fifty-eight neurons (30.9%) responded directly to acoustic stimulation with a latent period of 10–50 msec for 2–6 sec, 19 neurons (10.1%) generated double responses, linked with both the acoustic stimulus and subsequent conditioned-reflex movement, and 42 neurons (22.3%) did not respond to acoustic stimulation, although individual neurons of this group changed the level of their spontaneous activity in response to repeated conditioned stimulation, and this change was maintained for some tens of minutes. Extinction, differentiation, and conditioned inhibition all abolished conditioned-reflex movements, but each type of internal inhibition was accompanied by its own characteristic changes in the firing pattern of PGM neurons. Functional independence of neurons of the first and second groups was demonstrated during extinction and recovery of the conditioned-reflex. The results indicate the important role of PGM not only in the mechanism of the conditioned reflex, but also in the development of its internal inhibition.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 403–419, May–June, 1984.     

Connections of neurons of the cat somatosensory cortex with the thalamic relay nuclei

Of 103 neurons in the rostral part of the posterior sigmoid gyrus of the cat cortex 30 responded to stimulation of the ventro-posterolateral and ventrolateral nuclei of the thalamus (VPL and VL), 42 responded to stimulation of VL only, and 31 to stimulation of VPL only. It was shown by intracellular recording that stimulation of VPL induces a spike response with or without subsequent IPSPs in some neurons and an initial IPSP in others. The spike frequency of single neurons reached 60/sec, but the IPSP frequency never exceeded 10–20/sec. Stimulation of VL was accompanied by: a) antidromic spike responses; b) short-latency monosynaptic EPSPs and spikes capable of following a stimulation frequency of 100/sec; c) long-latency polysynaptic EPSPs and spikes appearing in response to stimulation at 4–8/sec; d) short-latency IPSPs; e) long-latency IPSPs increasing in intensity on repetition of infrequent stimuli. It is concluded that the afferent inputs from the relay nuclei to neurons of the somatosensory cortex are heterogeneous. An important role is postulated for recurrent inhibition in the genesis of the long-latency IPSPs arising in response to stimulation of VL, and for direct afferent inhibition during IPSPs evoked by stimulation of VPL. It is shown that the rostral part of the posterior sigmoid gyrus performs the role of somatic projection and motor cortex simultaneously.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 245–255, May–June, 1972.     

Effect of extracellular polarization on unit activity in the lateral geniculate bodies

Unit responses of the lateral geniculate bodies (LGB) to polarization of the cells through the recording microelectrode were investigated in acute experiments on cats anesthetized with Nembutal. Under the influence of anodic polarization the firing rate of the LGB cells clearly increased. Complete adaptation of the cells to the polarizing current was not observed during the time intervals investigated (5–10 min). Cathodic polarization by a current of 5–50 nA induced inhibitory effects; neurons with a single type of spontaneous activity under these circumstances generated volleys of 2–5 spikes. Off-responses were recorded in 75–85% of neurons. It is postulated that complex changes in unit activity produced by polarization may be due to the structural characteristics of the functional connections of the LGB neurons investigated. The change to grouped activity on the part of many of the neurons under the influence of cathodic polarization is evidently explained by the specific functional pattern of the synaptic system of the LGB cells.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 130–140, March–April, 1972.     

Effect of inhibition of prostaglandin biosynthesis on spike activity and chemical sensitivity of cortical neurons in rabbits

Experiments on unanesthetized, unrestrained rabbits using a technique of microiontophoresis showed that the non-narcotic analgesics aspirin, butadione, and indomethacin, which inhibit prostaglandin synthesis, have a marked effect on spontaneous firing and sensitivity of sensomotor cortical neurons to neurotransmitters (acetylcholine and noradrenalin). The non-narcotic analgesics in most cases inhibited spontaneous unit activity and potentiated responses to neurotransmitters. In some neurons the action of non-narcotic analgesics was to produce total but reversible inhibition of discharge activity and also of chemical sensitivity. The experimental results are discussed from the standpoint of the mechanisms of participation of prostaglandins in unit activity.P. K. Anokhin Research Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 130–134, March–April, 1982.     

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.     

Unitary responses of the caudate nucleus to direct stimulation

Unitary responses of the caudate nucleus to stimulation of various parts of it were investigated by extracellular recording. Latent periods of response discharges varied from 3.5 to 40 msec. Most neurons were excited by stimulation of the most rostral part of the head of the caudate nucleus. Irrespective of the site of stimulation, in most cases responses consisted of initial excitation in the form of one or, less frequently, two discharges followed by a period of depression of spontaneous activity. Recovery of activity took place gradually, without postinhibitory facilitation. No afterdischarges or periodic repetitions of spikes were observed after the initial response. Repetitive stimulation of the caudate nucleus showed that the neurons of this nucleus reproduce frequencies of stimulation badly above 30/sec, and under these circumstances in many cases they continued to discharge on average at a frequency of 5–15/sec. The results are examined from the standpoint of participation of the caudate nucleus in the formation of spindle activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 497–506, September–October, 1976.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

Interaction between visceral,somatic, and visual excitation on single neurons of the lateral geniculate body in cats

Acute experiments on cats anesthetized with pentobarbital and immobilized with diplacin or listhenon showed that visceral and somatic excitation may either facilitate or inhibit single unit activity in the lateral geniculate body evoked by photic stimulation. The manifestations of facilitation were: a modulatory type of enhancement of responses of silent neurons and neurons with a low level of spontaneous activity; enhancement of responses accompanied by simultaneous depression of spontaneous activity — a sensory contrast effect; enhancement of long-latency responses; appearance of a short-latency discharge from cells with an inhibitory response to light; the appearance of responses to light in neurons not responding previously or stabilization of responses in neurons responding to light irregularly. The inhibitory effects were manifested as immediate inhibition of responses, usually long-latency, and the filling up of the inhibitory pauses of the response to light with spikes, leading to a decrease in the signal-noise ratio. Somatic stimulation was more effective and more frequently evoked facilitation of responses to light (in 74% of cells). Similar results were obtained by stimulation of the mesencephalic reticular formation. Visceral excitation gave rise to facilitatory and inhibitory effects to an almost equal degree. The results show that excitation arising as the result of visceral and somatic stimulation affects the conduction of visual information in the neuronal system of the lateral geniculate body.Ivano-Frankovsk Medical Institute. Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 636–643, November–December, 1973.     

Analysis of spontaneous unit activity of the cat caudate nucleus

Spontaneous unit activity recorded extracellularly from the caudate nucleus in acute experiments on cats was analyzed. A graph of the sliding mean frequency, an interspike interval histogram, correlogram, intensity function, and histogram of correlation between adjacent intervals were plotted for the spontaneous activity of each neuron. The spontaneous activity of neurons of the caudate nucleus showed considerable variability in time and its mean frequency varied for different neurons from 0.5 to 20 spikes/sec. Depending on the temporal pattern of the spikes and also on the statistical indices, spontaneous unit activity in the caudate nucleus was conventionally divided into two types: single and grouped. A switch from one type of activity to the other was observed for the same neuron. On the basis of the data as a whole it is impossible to regard the spontaneous unit activity of the caudate nucleus as a simple random (Poissonian) spike train.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 369–376, July–August, 1977.     

Dynamics of single unit responses of the rabbit visual cortex to repetitive photic stimulation

Single unit responses in the visual cortex of the waking rabbit to repetitive photic stimulation at a frequency of once every 2.5 sec were studied. Depending on the total number of spikes in the response, the dynamics of the responses could be divided into two types: "fast" and "slow." From 5 to 15 stimuli were required to establish a stable level of response with changes of the first type, but 50 to 100 stimuli were needed for the response with changes of the second type. About 50% of all neurons did not change the characteristics of response. In the group of neurons with changing responses, partial habituation was found in 55–59% of cells; there were 25% of neurons with sensitization of discharge and 17–20% with a humpbacked type of response dynamics. A "slow" dynamics of unit responses in most cases was accompanied by changes in the duration of inhibitory pauses in the response; negative correlation of these values was observed in 65% of neurons.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 451–459, September–October, 1978.     

Hypothalamic influences on unit activity in the cat sensomotor cortex

Experiments on unanesthetized, immobilized cats showed different effects of individual hypothalamic nuclei on spontaneous unit activity in the sensomotor cortex. Compared with the posterior hypothalamic nucleus (PHN) and its anteromedial region (AMH), in response to stimulation of the lateral hypothalamic nucleus (LHN) changes in spontaneous activity were more frequently found. The ratio between activation and inhibitory responses was 36 and 36% for AMH, 51 and 30% for LHN, and 47 and 28% for PHN. An approximately equal number of sensomotor neurons (27–34%) gave tonic responses. Phasic changes in spontaneous activity were observed more often in response to stimulation of LHN, less frequently to stimulation of AMH and PHN. Responses of "nonpyramidal" neurons to stimulation of AMH and LHN were identical. "Pyramidal" units were more sensitive to LHN stimulation. Variations in hypothalamic effects depending on the type of response of sensomotor neurons to sensory stimuli were detected. Cells with tonic responses were more susceptible to influences of LHN and AMH than cells which responded by phasic changes in spontaneous activity to sensory stimuli. Fewer still positive responses were recorded in areactive neurons.Medical Institute, Chita. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 115–122, March–April, 1972.     

Microiontophoretic study of the effect of biogenic amines on unit activity in the rabbit visual cortex

The effect of acetylcholine, noradrenalin, and serotonin on spontaneous activity of visual cortical neurons and on their activity evoked by flashes, recorded extracellularly, was studied by microiontophoresis in unanesthetized rabbits. The ability of visual cortical neurons to respond to light does not correlate with their sensitivity to acetylcholine. This substance, which changes the spontaneous firing rate of many of the neurons tested, was less effective against their evoked activity. Noradrenalin had a powerful depressant action on both spontaneous and evoked activity of most neurons studied. Serotonin acted in different ways on the spontaneous and evoked activity of some neurons tested. It is postulated that acetylcholine mediates reticulo-cortical inputs, noradrenalin is a true inhibitory mediator in the cerebral cortex, and serotonin has a presynaptic action by preventing the liberation of natural mediators.     

Neuronal firing activity in the lateral vestibular nucleus during locomotion in the guinea pig

The effects of spontaneous locomotor activity on neuronal background firing in the lateral vestibular nucleus was investigated during experiments on decerebrate guinea pigs. The onset of rhythmic muscular activity in the extramities was found to produce a rise in the rate of such discharges, which increased from 10–15 to 100 spikes/sec in most neurons. A higher rate occurred as activity began in the ipsilateral forelimb extensor muscles (the stage corresponding to the end of the swing phase and start of the stance phase in the locomotor cycle). The alterations noted in vestibular neuronal activity during locomotion are thought to ensure the background of high anti-graveity muscle tonus against which rhythmic limb movements take place.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 536–541, September–October, 1991.     

Investigation of mechanisms of synaptic transmission in ampullae of Lorenzini in the skate

The effect of magnesium ions, L-glutamate (L-GLU), and the diethyl ester of glutamic acid (DEE-GLU) on temperature and electrical sensitivity of the ampullae of Lorenzini in skates was studied by the method of perfusion of the basal membrane of electroreceptor cells and recording spike activity from single nerve fibers. Addition of 10^–4–10^–5 M L-GLU to the solution was shown to cause an increase in the spontaneous discharge frequency of receptors with low initial level of activity (8–20 spikes/sec) and a decrease in receptors with spontaneous activity of 22–42 spikes/sec. In solution with an increased magnesium ion concentration (15–50 mM) both spontaneous and evoked receptor activity was blocked, Under these conditions the addition of L-GLU to the solution caused partial recovery of spontaneous receptor activity. Reversible blocking of spontaneous and evoked receptor activity was observed in a solution containing 10^–4–10^–3 M DEE-GLU. It is suggested that L-GLU is the synaptic transmitter in the ampullae of Lorenzini of the skate.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 292–298, May–June, 1981.     

Responses of caudate neurons to clicks in chronic experiments on cats

Spontaneous and evoked unit activity in response to repeated application of clicks at a frequency of 0.3–2.0 Hz in the caudate nucleus was studied by an extracellular recording technique in chronic experiments on cats. Four types of spontaneous unit activity in the caudate nucleus were distinguished. Altogether 44% of neurons tested responded by changes in spontaneous activity to clicks. Five types of responses of caudate neurons to clicks were discovered: phasic excitation, phasic inhibition, tonic activation, tonic inhibition, and mixed tonic responses; the commonest type was tonic activation. During prolonged stimulation by clicks extinction of the phasic responses was not observed. Complete or partial extinction of tonic responses in the course of frequent repetition of stimulation was observed in 33% of responding neurons. The question of possible convergence of specific and nonspecific influences on caudate neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 28–35, January–February, 1980.     

Responses of central auditory neurons to frequency-modulated stimuli

Unit responses of the inferior colliculi of albino rats to frequency-modulated stimuli were investigated. The number of spikes, firing pattern, and duration of the discharge were determined. Parameters of unit responses obtained with different directions of frequency modulation were compared with the results of testing the effect of constant-frequency tones on the neurons. The distinguishing features of the unit responses to stimuli with different directions of frequency modulation were compared with the characteristics of the frequency-threshold curve and the lateral inhibitory zones, taken as indices of the unit responses to constant-frequency tones. With a change in stimulus frequency upward or downward from the initial level the unit responses to both directions could be similar as regards the number of spikes per discharge and the firing pattern or could differ sharply depending on the direction or, finally, they could arise only if the stimulus frequency changed in one direction. In some cases selectivity for the direction of the change in stimulus frequency was due to the width and position of the lateral inhibitory zones. However, for one-third of the neurons tested analysis of the spatial characteristics of the excitatory and inhibitory zones alone was insufficient to explain the high selectivity in the formation of a response to a stimulus with frequency modulation in one direction only.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.3, pp.237–245, May–June, 1974.