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The present study comprises an attempt to investigate the influence of acetylcholine on the functional connections of the cortical cells and their frequency characteristics. The multineuronal activity was recorded in the sensorimotor cortex of immobilized and freely moving rats, and was subsequently analyzed using the method of cross-correlational analysis. In the first series of experiments, the influence of the neuromediator, acetylcholine (ACh), and calcium chelation, ethyleneglycol tetraacetate (EGTA), on the functional characteristics of adjacent neurons during the iontophoretic application of these substances to cells of the sensorimotor cortex of unanesthetized immobilized rats was investigated. In this case, the iontophoretic application of ACh led to a change in the frequency characteristics of individual neurons, and in the majority of cases did not influence the character of the interneuronal interactions. The application of EGTA led to a decrease in the average frequency of impulse activity for the majority of the neurons, as well as to the disappearance, independent of the running frequency, of excitatory connections in the cross-correlograms, with their subsequent recovery following the termination of exposure to the EGTA. In the second series of experiments, carried out in freely moving rats with a chronically implanted recording electrode, the systemic administration of the acetylcholinesterase blocker, galantamine, led to a substantial intensification of the impulse activity of the cortical neurons, and at the same time did not exert a substantial influence on the network activity of the same neurons. The hypothesis is advanced that the intracortical neuronal interactions may be accomplished independently of extracortical influences that are expressed in the fluctuations of the baseline impulse activity of individual cells. The qualitative assessment that was carried out of the influence of ACh on the functional characteristics of the cortical neurons does not make it possible to identify an influence of ACh (including a modulatory influence) on the formation of intracortical connections. The methods used in this investigation may be used for a further study of the influence of various mediator systems of the brain on the functioning of intracortical interneuronal connections.

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An attempt is made to study the influence of acetylcholine on functional connections of cortical neurons and their frequency characteristics. Multiunit activity was recorded in the sensorimotor cortex of immobilized and freely moving rats. Crosscorrelation analysis was used. Influence of acetylcholine (Ach) and Ca chelator ethyleneglicoltetraacetat (EGTA) on the functional characteristics of the neighbouring neurons was studied in the first series of experiments. The substances were iontophoretically applied to the sensorimotor cortex neurons of the immobilized unanesthetized rats. Application of Ach led to variation in the frequency characteristics of single neurons and in the majority cases did not affect the neuronal interrelations. EGTA application, independently on the background frequency of the neuronal activity, resulted in disappearance of interneuronal connections which recovered after the end of EGTA effect. The second series of experiments was carried out in freely moving rats. System injection of galantamine essentially increased the frequency of activity of the cortical neurons not affecting their network activity. We suppose that intracortical relations can be realized independently on the extracortical influences which are manifested in variations in the background impulsation of the single neurons. Qualitative estimation of Ach influence on the functional characteristics of the cortical neurons do not reveal Ach effects on formation of intracortical connections. The technique used by us may be applied in further studies of intracortical neurons connections.

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The main outcome of the experiments described in the paper is an idea on the gnostic cortical microset. Multineuronal activity recorded from the motor cortex of cats with a conditioned response to time and the following cross-correlation analysis revealed a strict distribution of interneuronal connections within the microsystems (between the adjacent neurons) and variable connections between the remote neurons during the active waiting stage of two minute interval. Additional analysis of the narrow (0.5 ms) peaks of the histograms allowed to form a view on the synaptic interaction in time. It was found that there was different temporal distribution of the spikes in the peak obtained due to correlograms of neuronal pairs. Some cortical neurons demonstrated a visible synaptic activation at the end of the waiting period when other signs of the temporary behaviour were absent. Pharmacological testing functional interneuronal connections with acetylcholine and Ca(2+)-suppressing drug EGTA have raised a question on the neurochemical specificity of the intra- and extracortical synapses.

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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.

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Experimental data are presented on reorganizations of intra- and interanalyzer functional connections of neurones in the course of conditioning, by interval cross-histograms of two impulse series, and notions on neuronal organization of local and spread conditioned states are formulated. Numerous varieties of the analysis of systemic, interconnected activity of cortical neurones in the process of learning convince of the fact that individual and integrative neuronal functions characterize different qualitative levels of their activity. The integrative function of neurones shows various degrees of complicacy and specialization. The local conditioned state is considered to represent functional integration of neurones in cortical microregions, and the spread conditioned state--as neuronal integration between cortical projection zones. The interaction of neurones in the cortical projection of conditioned stimulus is more multiform and complex than that in the motor cortex. During the elaboration of inhibitory conditioned reflex there occurs a reorganization of the cortical systemic activity in the projection zone of the conditioned stimulus and a decrease of intensity of distant connections.

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A statistical analysis has been made of the interaction of the auditory cortex units in alert cats with chronically implanted electrodes. Three neurones with an amplitude ratio of 4:2:1 were singled out from the multineuronal activity. The dependence between the firing of two neurones was determined by the cross interval histograms. The relationships between 78 pairs of units were studied in 26 three units microsystems. About a third of the studied pairs functioned independently. The number of pairs with one-way and two-way connections was about equal (26 and 30 respectively). The neurones which generated spikes of high and medium amplitude, had the largest number of two-way connections. One-way connections were equally represented in all the three neurones, though with regard to direction they depended on the amplitude characteristics of the spikes. In neurones with large and medium spikes, output connections predominated, while in neurones with small spikes input connections predominated considerably. The connection could be of inhibitory, excitatory or mixed type. The inhibitory type of connections was the most frequent occurrence (57 out of 86). At prolonged recording (6 to 16 min) of spike activity, most of the functional connections persisted.

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