Tissue culture study of unit activity of the rat cerebral cortex

Spontaneous unit activity and morphological characteristics of visual cortical neurons from young rats aged 1 and 2 days were investigated during long-term culture (up to 34 days) of explants in vitro. Three types of spontaneous unit activity were found: single spikes, volleys, and grouped discharges. The types of spontaneous activity were found to depend on the duration of cultivation of the brain tissue. The discharge of single spikes, characteristic of neurons during the first 7–15 days in culture, subsequently was replaced by grouped discharges or volleys of spikes. The changes in unit activity were shown to coincide in time with morphological maturation of the synapses. In experiments in which strychnine (10 µg/ml) was added to the culture medium, a marked increase was observed in the mean frequency of spontaneous unit activity, accompanied by the appearance of discrete series of volley-type discharges. The genesis of spontaneous cortical unit activity is discussed on the basis of these findings.     

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

Spontaneous activity of slow- and fast-adapted abdominal stretch receptor (SAR and FAR) of the crayfish and their activity evoked by adequate stimulation were investigated in the presence of efferent regulation. Activity of the receptors was shown to be under effective inhibitory control of two central neurons, principal and accessory; activity of these neurons, in turn, is determined by the current receptor activity. The closest interaction is found between SAR and the principal inhibitory neuron. Two types of efferent regulatory action of this neuron were discovered: grouped and continuous. Its powerful discharges (up to 361 spikes) arising in response to only one SAR afferent impulse are described. The character of synaptic connections between the peripheral and central neurons is discussed.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. 3, pp. 317–327, May–June, 1972.     

Spontaneous unit activity in anterior (limbic) nuclei of rabbit thalamus

Spontaneous spike activity in three anterior (limbic) neurons of the thalamic nucleus was studied by means of extracellular recording during chronic experiments on anesthetized rabbits. Neurons of the anteroventral nucleus showed high mean rate (24.8±5.8 spikes/sec) and varying structure of spike discharges ("inactivating" bursts of discharges, modulations in delta- and theta-rhythms, and bursts of discharges with a spindle rhythm of 12–14 Hz). "Inactivating" bursts of discharges alternating with single discharges predominated in the activity of neurons of the anteromedial nucleus (mean rate 10.0±1.4 spikes/sec). Activity of the anterodorsal nucleus could be clearly distinguished by the predominance of high-frequency groups of spikes (mean group frequency 67±5 spikes/sec) with prolonged intervals between groups.Institute of Biological Physics, Academy of Sciences of the USSR, Puschino, Moscow Province. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 579–586, September–October, 1985.     

Various forms of potentials recorded from caudate nucleus neurons

Spontaneous and evoked activity of caudate nucleus neurons was recorded extracellularly in acute experiments on cats. Different forms of potentials were found by analysis of the results. The potentials recorded belong to three types: ordinary action potentials; prepotentials or incomplete spikes differing from ordinary action potentials in their lower amplitude and slower decline, and complex discharges in which a spike of somewhat reduced amplitude is followed by a slow positive-negative wave. In the spontaneous activity prepotentials were observed both in complete action potentials and in isolation. The frequency of the complex discharges was 0.5–1 per second. The slow wave of these discharges blocked prepotential and action potential formation. The origin of these forms of potentials in neurons of the caudate nucleus is discussed and they are compared with analogous forms of potentials described for the Purkinje cells of the cerebellum.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukranian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 149–156, March–April, 1977.     

Dendritic action potentials of pyramidal tract neurons in the cat sensorimotor cortex

The intracellular activity of pyramidal tract neurons was studied during electrical stimulation of ventrolateral and ventroposterolateral thalamic nuclei in acute experiments on cats immobilized by myorelaxants. Somatic action potentials were observed and spontaneous spikes were also produced by single and rhythmic stimulation of the thalamic nuclei at the rate of 8–14 Hz, by iontophoretic application of strychnine, and by intracellular depolarizing current pulses. These potentials had a relatively low and variable amplitude of 5–60 mV and are presumed to be dendritic action potentials. It is postulated that these variable potentials arise in the dendrites of pyramidal neurons with multiple zones generating such activity. No interaction was observed where somatic and dendritic action potentials occur simultaneously. The possible functional role of dendritic action potentials is discussed.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 435–443, July–August, 1986.     

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.     

Effect of cortisol microiontophoresis on discharge time structure of dorsal hippocampal neurons in rabbits

The effect of microiontophoretic application of cortisol to single neurons of the dorsal hippocampus on the character of distribution of interspike intervals in their discharges was studied in chronic experiments on rabbits. Cortisol modified the time structure of regular and rhythmic discharges of hippocampal neurons. Regularization of discharges in the form of bursting activity appeared as the result of cortisol in cells with irregular spontaneous activity. Activity of more than half of the neurons, in which bursting discharges corresponded in frequency to the theta-rhythm, was intensified as a result of microapplication of cortisol. In neurons discharging complex spikes, in which under normal conditions a phenomenon of reduction of spike amplitude was observed within each burst, no definite rule as regards changes in the time structure of the discharges could be observed after administration of the hormone. It is suggested that cortisol plays a modulating role in mechanisms of generation of spike activity by hippocampal neurons.P. K. Anokhin Research Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 628–635, November–December, 1981.     

Tranformation of long reticulofugal spike trains by interneurons connected monosynaptically with the reticulospinal tract

Characteristics of transmission of activity evoked by stimulation of the reticular formation through interneurons located in the ventromedial zones of the gray matter of the lumbar division of the spinal cord and connected monosynaptically with reticulospinal fibers were investigated in cats. Responses of the neurons to relatively low-frequency (not exceeding 80–100/sec) stimulation consisted mainly of stationary discharges; with a further increase in frequency the response became nonstationary (the initial, relatively high-frequency discharge was followed by partial or complete suppression of the discharge). The maximal frequency of the initial phase of the response to high (over 400/sec) frequencies of stimulation was 180–230 spikes/sec. The "transmission factor" (ratio between the frequency of spikes in the response to the frequency of stimulation), calculated for stationary discharges, reached 0.7–0.8 at low frequencies of stimulation, and then decreased significantly. On the basis of the statistical characteristics of the stationary portions of the evoked activity and analysis of these data by the use of a mathematical model, indirect estimates were obtained of the parameters of processes lying at the basis of the transforming properties of this cell population.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 278–286, May–June, 1978.     

Role of hippocampal neurons in theta-wave generation

Temporal relations between hippocampal unit activity and phases of the theta-waves were studied in unanesthetized rabbits immobilized with tubocurarine. When spontaneous thetarhythm potentials were recorded layer by layer from the dorsal hippocampus, a change in their polarity was observed 0.15–0.2 mm deeper than the pyramidal layer (i.e., in the radial layer). Most hippocampal neurons fired synchronously with the extracellular thetawaves. The numerous pyramidal cells, in which the spontaneous activity was inhibited during stimulation of the contralateral hippocampus and sciatic nerve and a hyperpolarization potential developed, were excited mainly during the positive phase of the theta-waves. Intracellular recording showed that their membrane potential decreased during the positive phase and increased during the negative phase. The less numerous basket cells, whose response to stimulation of the contralateral hippocampus consisted of a short high-frequency volley of spikes, and whose response to sciatic nerve stimulation was marked by a prolonged increase of frequency of the spontaneous discharges, were activated mainly during the negative phase of the theta-waves. It is concluded from these findings that inhibitory mechanisms play a role in the theta-activity of the hippocampus. It is postulated that the extracellular theta-waves are integral EPSPs of the basal dendrites and of the proximal segments of the apical dendrites, and that IPSPs of the pyramidal cell bodies play the principal role in the generation of the intracellular theta-rhythm.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 531–539, September–October, 1972.     

Types of spontaneous discharges of muscle receptors

Characteristics of discharges of 462 muslce spindle receptors located in the deefferented triceps surae muscle with a divided tendon were analyzed in anesthetized cats. Of the total number, 205 units had spontaneous activity which, depending on its stability, could be divided into three types. A long continuous spike train was generated by 87% of units. Distributions of interspike intervals were unimodal and symmetrical. Spontaneous activity of this type was more regular in secondary than in primary endings. Action potentials in 8% of units were grouped in volleys and interval distributions were bimodal. Spontaneous activity of the remaining 5% of units was characterized by sporadically appearing spikes with long intervals between them. The first two types of spontaneous activity cannot be placed in the category of stochastic processes. Threshold discharges during static stretching of the muscle sufficient to cause the appearance of a long spike train were studied in 231 of 257 initially "silent" units. By the same criteria these discharges were divided into corresponding types. Comparison of the characteristics of spontaneous activity and evoked responses suggests that they share the same mechanism of origin. It is concluded that the spontaneous discharge can be regarded as a static response of the receptors due not to an externally applied stretching load, but to the action of internal factors, depending on interaction between extrafusal and intrafusal muscle fibers.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 315–321, May–June, 1981.     

Character of evoked responses of the dorsomedial thalamic nucleus to stimulation of the periamygdalar cortex and area amygdaloidea anterior in rats

Characteristics of focal potentials and single unit responses of the dorsomedial nucleus of the thalamus to electrical stimulation of the anterior periamygdalar cortex (APC) and area amygdaloidea anterior (AAA) were compared in acute experiments on rats. Differences were found in the parameters, dynamics, and duration of the recovery cycle of focal potentials in response to stimulation of APC and AAA. Stimulation of APC and AAA was accompanied by changes in the discharges of 26.9 and 19.2% of neurons studied respectively. Four types of unit responses are described: activating (64.3% of responding cells), biphasic activating (14.3%), inhibitory or inhibitory-activating (14.3%), and complex (7.1%). Spontaneous activity was exhibited by 25% of reacting cells. Stimulation of APC was shown to give rise to both shortlatency (12–18 msec) and long-latency (23–66 msec) phasic activating responses of the neurons whereas the latent periods of the analogous responses to stimulation of AAA exceeded 20 msec (from 21 to 136 msec). Unit responses of the second type consisted of a principal phasic response of three or four spikes with mean latent periods of 9–19.1 msec, preceded by a single short-latency (2.9–4.1 msec) spike. Responses of the first two types were characteristic of 92.9 and 64.3% of neurons responding to stimulation of APC and AAA respectively.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 604–611, November–December, 1981.     

Effect of pentobarbital on unit activity of reticular and ventrolateral thalamic nuclei in cats

Responses of single units in the reticular and ventrolateral thalamic nuclei were studied in acute experiments on curarized cats before and after intravenous injection of small doses (0.5–15 mg/kg) of pentobarbital, with simultaneous derivation of activity by two electrodes. After injection of pentobarbital, unit activity in the reticular nucleus consisted of high-frequency grouped (52.5% of 40 neurons) or continuous (30%) discharges as long as barbiturate spindles were present in the electrocorticogram. Activity of only four neurons (10%) of this nucleus was inhibited during the presence of spindles. In all other neurons of the reticular nucleus (7.5%) the character of discharges was unchanged after injection of pentobarbital. The appearance of grouped discharges, repeated several times (66.5% of 40 neurons), or blocking of activity (30%) throughout the period of spindle recording was observed in neurons of the ventrolateral nucleus. The remaining neurons of that nucleus (3.5%) did not respond to intravenous pentobarbital. The appearance of high-frequency discharges in neurons of the reticular nucleus while spindles were recorded coincided with a period of silence in neurons of the ventrolateral nucleus (58.5% of 34 pairs of neurons). High-frequency electrical stimulation of the mesencephalic reticular formation led to asynchronous activation of neurons of the ventrolateral nucleus (82%) and inhibition of unit activity in the reticular nucleus (88%).I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 517–524, September–October, 1982.     

Effect of noradrenalin and serotonin on responses of area CA3 neurons evoked in guinea pig hippocampal slices by electrical stimulation of mossy fibers

The effect of noradrenalin (NA) and serotonin (5-HT) on responses of area CA₃ cells evoked by electrical stimulation of mossy fibers was studied in slices of guinea pig hippocampus survivingin vitro. Both substances, which modify the general level and organization of spontaneous activity, also affected responses of area CA₃ cells. Changes in magnitude and structure of the response usually correlated with corresponding changes in spontaneous activity. In certain cases NA, which lowered the frequency of spontaneous activity but increased its relative content of "complex discharges" and also the number of reduced action potentials in the complex discharge, also led to an increase in the response to stimulation. 5-HT evoked periodic grouped activity in some cells and led to the appearance of such grouped discharges for the first time in the responses of other cells. Unlike NA, 5-HT caused prolonged (up to 40 min) after-facilitation of the response and an increase in spontaneous discharge frequency.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 410–417, July–August, 1982.     

Rhythmic background thalamic neuronal activity in patients with extrapyramidal motor disorders

The background activity of 123 thalamic neurons was recorded in 30 patients with motor extrapyramidal disorders applying microelectrode techniques to neurosurgical practice. Recordings were taken from the ventro-oral anterior and posterior thalamic nuclei and the adjacent reticular nucleus. A computer analysis was performed of neuronal activity in 44 units and plots produced of autocorrelation and spectral density functions. In patients with parkinsonism and double athetosis, rhythmic activity was found in 48% of cells. A wide variety of regular fluctuations in background neuronal discharges was noted: in the range of theta and delta rhythms (5–7 and 1–4 Hz respectively) with a periodicity of seconds (2–10 sec) and decaseconds (15–40 sec). It was thought possible that several types of regular waves may coexist: phenomena of 2 or 3 accelerated waves and reduced frequency of spike activity of differing periodicity were observed in eight neurons within the same train of spikes. The origin and significance of rhythmically occurring changes in thalamic neuronal spike activity are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR; Institute of Neurosurgery, Ministry of Public Health of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 192–201, March–April, 1987.     

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.     

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.     

Neuronal responses of a chronically isolated slab of auditory cortex to intracortical stimulation during paroxysmal electrical activity in cats

Responses of 155 neurons 3 weeks after neuronal isolation of a slab of auditory cortex (area AI) to single intracortical stimulating pulses at the level of layer IV were studied in unanesthetized, curarized cats during paroxysmal electrical activity evoked by series of high-frequency (10–20 Hz) electrical stimulation by a current 2–5 times above threshold for the direct cortical response. In response to such stimulation a discharge of paroxysmal electrical activity, lasting from a few seconds to tens of seconds, appeared in the slab. As a rule it consisted of two phases — tonic and clonic. This indicates that cortical neurons can form both phases of paroxysmal cortical activity. Depending on behavior of the neurons during paroxysmal electrical activity and preservation of their ability to respond to intracortical stimulation at this time, all cells tested in the isolated slab were divided into four groups. Their distribution layer by layer and by duration of latent periods was studied. Two-thirds of the neurons tested were shown to generate spike activity during paroxysmal discharges whereas the rest exhibited no such activity. A special role of neurons in layer II in generation of paroxysmal activity in the isolated slab was noted. The view is expressed that at each moment functional neuronal circuits, independent of each other, exist in the slab and also, evidently in the intact cortex, which can interact with one another when conditions change.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 3–11, January–February, 1984.     

Habituation of postsynaptic unit responses of the cat motor cortex to stimuli of different modalities

Habituation (extinction) of postsynaptic unit responses of the cat motor cortex to repetitive electrodermal, photic, acoustic, and combined bimodal stimulation was investigated by intracellular recording. Habituation was shown by a decrease in the number of spikes per grouped discharge and a decrease in the amplitude and duration of the EPSPs, and sometimes IPSPs, on repetition of the stimulus. The way in which the course of habituation depends on the modality and duration of stimulation (at a constant frequency of 1/sec) is examined. Habituation of postsynaptic responses to sensory stimuli is observed with neurons of different functional groups, namely identified neurons of pyramidal tract and unidentified neurons, some of which were evidently pyramidal neurons and interneurons. The hypothesis is put forward that the habituation of PSPs of the cortical neurons is based on processes taking place mainly at the subcortical level.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 545–553, September–October, 1972.     

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.     

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.