Analysis of spontaneous unit activity in the cat pyramidal tract

For a statistical analysis of spontaneous activity of cortical pyramidal neurons (PN) of the cat, recordings were obtained from axons of those neurons descending in the lateral pyramidal tract in lumbar segments of the spinal cord. Spontaneous activity of all investigated PN is not random in sequence but has a complex temporal structure. Three types of spontaneous activity were distinguished by the character of distribution of the interspike intervals (ISI); the degree of grouping of the spikes into volleys separated by long intervals increases from type I to type III. Type III is more often found in PN with fast-conducting axons. As a rule the number of volleys in the spontaneous activity differed from that expected by the hypothesis of random spike sequence. In some cases repetition of volleys with an identical, or nearly identical, temporal structure was observed. It is postulated that the type of spontaneous activity is determined by the functional state of the neuron and by its morphological properties. Experiments were carried out on two groups of animals: 1) briefly anesthetized a long time before the recording was obtained, and then immobilized; 2) anesthetized with chloralose and Nembutal. The differences between the character of spontaneous PN activity were mainly in the degree of grouping of the spikes (which was greater in the second group). Significant positive correlation was found between the velocity of conduction along the PN axon and the mean ISI of the spontaneous activity.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 3–11, January–February, 1972.     

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.     

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.     

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.     

Spontaneous unit activity in the rabbit limbic cortex

Spontaneous unit activity in different parts of the limbic cortex, recorded extracellularly in waking rabbits during chronic experiments, was analyzed. Attention was paid particularly to unit activity in theta- and delta-rhythms. Theta-modulation was found in a small proportion (5–12%) of neurons in all parts except the lateral entorhinal cortex. Delta-activity was found in all structures tested but its characteristics varied. In the subiculum (45% of neurons) it consists of short, high-frequency discharges with long pauses, in the entorhinal cortex (22%) opposite characteristics were found (long loosely packed bursts with short intervals between them). Activating influences raised the frequency and increased the resistance of the theta component and desynchronized the delta volleys in the subiculum and most other structures; in the entorhinal cortex under these circumstances the density of the volleys of spikes was increased but without any change in their frequency or regularity. The spectral composition of unit activity in the presubiculum was mixed. The nature of rhythmic modulation of unit activity in areas of the limbic cortex is discussed.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 753–760, November–December, 1984.     

Pyramidal unit activity in unanesthetized cats

Pyramidal unit activity in unanesthetized cats at rest and during voluntary movement was recorded by a microelectrode technique from the motor cortex for the forelimb. Some pyramidal neurons were not spontaneously active. The conduction velocity along the axon of these neurons was sometimes high (up to 71.5 m/sec), sometimes low (up to 11.2 m/sec). The remaining pyramidal neurons had spontaneous activity with a mean frequency of 1.29 to 43 spikes/sec. Analysis of interspike interval histograms of spontaneous activity and of autocorrelation histograms showed grouping of the spikes into volleys in most pyramidal neurons (irrespective of the conduction velocity). During voluntary movements the change in the activity of many pyramidal units correlated with changes in the EMG. The firing rate of the pyramidal neurons under these circumstances began to rise at least 50 msec before the increase in amplitude of the EMG and it remained high throughout the movement. The firing rate of most neurons during movement was 40–60/sec. The results are compared with those obtained by other workers who studied pyramidal unit activity of monkeys during voluntary movement.     

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 destruction of afferent inputs on spontaneous unit activity and character of neuronal interconnection in the rat neostriatum

The effect of destruction of afferent inputs on relations between types of spontaneous unit activity, its mean frequency, the distribution of minimal and maximal intervals, and the character of neuronal interconnection in the neostriatum was studied in acute experiments on rats immobilized with D-tubocurarine. In addition, spontaneous activity derived from neurons in slices of rat neostriatum was analyzed. Spontaneous activity of grouped type was not observed, and no positive symmetrical maxima in the zero region were present on graphs of cross-correlation function. The results of the investigation showed that the grouped type of spontaneous activity is determined by activity of the cortical input whereas activity of the thalamic input has a tendency to prevent the development of this type of neostriatal unit activity. Activation of the cortical input also was shown to be probably responsible for the presence of a positive symmetrical peak on the cross-correlation function graph for neurons with the grouped type of spontaneous activity.Institute of Biological Physics, Academy of Sciences of the USSR, Puchchino-on-Oka. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 110–115, January–February, 1984.     

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.     

Synaptic mechanisms of spike generation in bursts by neurons of the carp tectum and olfactory bulb

Synaptic mechanisms of burst activity generation in certain neurons of the tectum opticum and mechanisms of generation of stimulation-induced group discharges by certain secondary neurons of the olfactory bulb were analyzed in carp (Cyprinus carpio L.). Spikes of the spontaneous discharge in neurons of the tectum were accompanied by depolarizing after-potentials, which caused the burst discharges of these cells. Evidence is given in support of the synaptic nature of the after-potential; it is suggested that it is generated by a recurrent collateral mechanism. Synaptic bombardment causing the appearance of a group discharge in olfactory bulb neurons and groups of spikes in their spontaneous activity was found to be intermittent in character. These features of unit activity in the olfactory bulb are shown to be connected with the presence of excitatory synaptic interaction between several neurons, probably dendro-dendritic in nature.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiay, Vol. 14, No. 5, pp. 483–490, September–October, 1982.     

Structure of background neuronal activity in thin slices of guinea-pig neocortex

We recorded background neuronal discharges extracellularly in guinea-pig cerebral cortex slices maintainedin vitro. The following types of activity were delineated: 1) regular single discharges (38.5%), 2) irregular spikes (6.5%), 3) bursts (6.5%), 4) burst-and-single discharge (mixed) activity (26.5%), 5) group discharges (2.5%), 6) multicellular volleys (18.5%). Each of these types corresponds to a characteristic distribution of interspike intervals in the form of an autocorrelogram. Regular pacemaker-type discharges, which are never observed in normal or isolated cortex, appeared in small volumes of grey matter and in the absence of afferentation.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 441–449, July–August, 1985.     

Multicellular discharges in the somatosensory cortex of cats at rest and during spontaneous EEG activation

Multicellular activity and the EEG were recorded from the somatosensory cortex by means of metal microelectrodes 30 µ in diameter in chronic experiments on waking unrestrained cats. Unit activity was separated into three different amplitudes by means of a discriminator. Three types of spontaneous activity were distinguished: with continuous, burst, and grouped discharges. Despite the outwardly identical picture of the spontaneous EEG activation reaction, parallel processes, differing in sign and distribution of unit activity were discovered in the neuron population. Their combinations were very varied. This activity could increase in frequency at all amplitude levels or at only one or two levels, accompanied by inhibition of discharges (or by no change) at other levels. The character of reorganization was shown to depend largely on the degree of the spontaneous EEG activation reaction and on the type of spontaneous unit activity. Computer analysis of the changes in the mean discharge frequency showed that during EEG activation stimulation of unit activity (55%) predominated over depression (21%). In some cell populations the sequence of discharges was altered without any change in mean frequency. The experimental results are discussed from the standpoint of the role of unit activity in spontaneous EEG activation.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 339–348, July–August, 1980.     

Formation of spontaneous and evoked unit activity in organotypical hippocampal tissue culture

Spontaneous and evoked single unit activity of Ammon's horn and the dentate fascia was investigated by extracellular recording in organotypical explants of neonatal mouse hippocampus during the first 2 weeks in culture. Three main types of spontaneous activity were observed: single, group, and volley. After the fifth to sixth day in culture the neurons were found to respond to stimulation of the entorhinal cortex and dentate fascia. Both short-latency (evidently monosynaptic) and long-latency responses were observed, and they usually varied if the stimulus was repeated. The appearance of evoked unit activity in the explants is considered to be due to maturation of synaptic contacts at axon endings of granule cells and perforant path, the formation of which continues during culture.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 257–266, May–June, 1977.     

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.     

The amplitude principle of the structural-functional classification of cortical neurons

Some literature and author's experimental data are presented on functional and morphological characteristics of nerve cells by their electrophysiological parameters. The proposition is substantiated that in multineuron discharges reflecting the activity of microgroups of neighbouring cells, the absolute size of impulses indicates the distance of cortical neurones from the tip of the electrode, while amplitudes correlation may characterize the size of the cell and some of its functional properties. Arguments for this proposition are: latencies of impulse responses to afferent and antidromic stimulations and amplitude changes of multineuronal activity during movement of the electrode through the cortex thickness in acute experiments. As the electrode (with the tip diameter of 50 mcm) approaches a microgroup of neurons, the amplitude of the recorded impulse discharges increases, while the relation of big spikes to small ones remains almost the same.     

Effect of electrical stimulation of the septum on subicular neurons with different kinds of spontaneous activity in rabbits

The effect of electrical stimulation of the medial nucleus of the septum and of hippocampal area CA₁ on subicular neurons with three different types of spontaneous activity (with theta-modulation, with delta-modulation and complex spikes, and with irregular single-spike activity) was studied in unanesthetized rabbits by extracellular recording of unit activity. Cells with theta-activity were found to respond in a distinctive functional manner to stimulation of the medial nucleus of the septum: Their reactivity was higher but latent periods of their responses were much shorter than those of cells with delta-activity and irregular discharges. Stability of modulation of theta-cell activity increased both during and after stimulation of the medial septal nucleus. Electrical stimulation of hippocampal area CA₁, on the other hand, led to disappearance of rhythm modulation. Average response latencies of all three types of cells to stimulation of area CA₁ were equal. The results indicate special properties of the septal input to subicular cells with theta-modulation.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 326–333, May–June, 1985.     

Spike Discharge Patterns of Spontaneous and Continuously Stimulated Activity in the Cochlear Nucleus of Anesthetized Cats

Interspike interval histograms of spontaneous and stimulated activity were computed from spike discharges of single units in the cochlear nucleus. These histograms indicate that a number of different types of spontaneous discharge patterns exist in the nucleus. The type of spontaneous activity of a given unit is related to its activity in response to continuous tones. Correlations were found between the discharge patterns of units and their anatomical locations within the nucleus.     

Unit activity in an epileptic focus formed in the cat motor cortex with tetanus toxin

Single unit activity was recorded intracellularly in the zone of an epileptic focus produced by injection of tetanus toxin into the cerebral cortex of cats. Epileptic activity of all neurons tested correlated with cortical discharges between fits. A group of neurons with continuous spontaneous activity, in which a steady fall of membrane potential and cyclic changes in the frequency of the spike discharges were observed was distinguished. In these neurons paroxysmal depolarization changes of membrane potential were found in the discharges between fits, without subsequent hyperpolarization of the membrane. Hyperpolarization potentials after paroxysmal depolarization shifts could be observed in neurons of other groups. The role of neurons of the different groups in the formation of an "epileptic aggregate," the main generator of pathologically enhanced excitation, is discussed.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Institute of Clinical and Experimental Neurology, Ministry of Health of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 582–589, November–December, 1978.     

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.     

Action of calcitonin gene-related peptide (CGRP) and substance P on neurons in the insular cortex and the modulation of taste responses in the rat

Using multibarrel electrodes, recordings were made from single neurons in the insular cortex including the cortical taste area (CTA) of urethane-anesthetized rats. The effects of an iontophoretic application of calcitonin gene-related peptide (CGRP) and substance P (SP) on the spontaneous discharges and taste responses were tested. In a total sample of neurons (mostly non-taste), CGRP affected the spontaneous discharges in 35.6% of the 571 neurons studied and SP in 38.3% of the 775 neurons studied. The effects were mostly (approximately 85-87%) facilitatory. Peptide-sensitive neurons were found at a similar frequency in all three insular areas-granular, dysgranular and agranular (areas GI, DI and AI). This is in contrast to previous reports that CGRP receptors were rich in area DI and CGRP-immunoreactive afferents numerous in area AI, but consistent with previous reports that the distribution of SP receptors and SP fibers was dense in the insular cortex. In approximately 40% of the 76 taste neurons recorded from areas GI and DI, the peptides affected the spontaneous discharges (mostly facilitated). When the taste responses were examined during application of the peptides, significant (mainly depressant) effects were seen in 61% of 18 neurons for CGRP and in 70.5% of 17 for SP. Such effects were not recognized on responses to specific taste stimuli and were not correlated with the effects on the spontaneous discharges. The findings indicate that both peptides modify taste coding in CTA neurons presynaptically and/or postsynaptically, independently of the existence of receptors on the neurons.