Cross-correlation analysis of the background activity of visual cortex cells separated by different distances in the alert rabbit

Values of correlation coefficients (CC) and forms of cross-correlation functions of impulse activity were studied in neurones recorded with one microelectrode or simultaneously with two sticked together microelectrodes with tangential distance between tips of 70 and 140 mcm. Three main types of cross-correlation functions were singled out differing by peaks form and modes positions. The greatest variety of forms and the greatest percentage of significantly correlated discharges of cellular pairs were found among the neurones recorded with one electrode. Mean CC of cells recorded with one electrode was significantly greater than mean CC of the neurones recorded with two microelectrodes. Comparison of the character of intercellular correlation with amplitudes of recorded spikes showed that discharges of neurones with greater amplitude mainly forestalled discharges of cells with low amplitude.     

An analysis of interneuronal connections in the auditory cortex of awake cats]

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.     

Temporal structure of the spike trains of neuronal pairs in the neocortex during calm wakefulness in rabbits

For revealing the conjugation of impulse activity of simultaneously recorded neurones in the visual and sensorimotor areas of rabbits neocortex, histograms were built of cross- and autocorrelation (CCH and ACH) of their discharges sequences. From successions of discharges of the visual cortex neurones, forming pairs of cells acting in correlation, spikes were singled out conjugated with neuronal discharges in the sensorimotor area, and their ACHs were built. In 77% of cases a resemblance was observed of temporal structure of conjugated discharges and real spike sequences, in 23%--there was no such resemblance. Analysis of conjugated discharges ACHs showed that they appeared predominantly periodically (87% of cases). The number of fragments with periodic discharges frequency within delta-frequency range from 3 to 4 Hz prevailed.     

Temporal structure of the spike trains in the neuronal impulses of the visual and sensorimotor areas of the rabbit neocortex during conditioned reflex activity

Conjugated spikes were singled out from successions of discharges of neurones in the rabbit's visual and sensorimotor neocortical areas acting in correlation. Their temporal structure was studied at intersignal intervals in transswitching of defensive positive and inhibitory conditioned reflexes and also in pseudoconditioning. The obtained results testify that conjugated discharges appeared for the most part periodically (in the average in 85% of fragments of unit activity). At positive and inhibitory conditioned reflexes, the frequency of periodical conjugated discharges belonged in most cases to the theta-rhythm range. At pseudoconditioning, periodical conjugated discharges were in the main of frequencies of delta-range (up to 4 Hz). The obtained results testify about a great significance of cortical neurones interaction in theta-range frequency at conditioned activity.     

Plastic changes of the network properties of neurons during learning in the cat

Functional connections between neurones of various types in microareas and between microareas of the motor cortex in cats have been studied during elaboration of an electro-defensive reflex to sound. A difference has been shown between neighbouring neurones in formation of their contacts with nearby neurones located within an area of 500 mc. Neurones generating spikes of high amplitude had more active "outputs" to neurones situated at different distances, while neurones generating spikes of low amplitude had more active "inputs" to them. On the other hand, as a result of conditioning "inputs" to distant neurones underwent more significant changes in the first type of neurones, and in the second type--the "outputs" changed more markedly.     

Cross-correlation as a method for discriminating impulses on multineuronal recordings

Impulses series, singled out from multineuronal activity by means of amplitude discriminator, were analyzed by creating crosscorrelation histograms. The authors consider that in studying of net brain activity with crosscorrelation method of analysis "window" discrimination of impulses series in multineuronal record is a quite correct method and may be used along with discrimination of spikes by form. It is shown that the size of the "window", used for singling out of separate impulses series, is not a determining parameter in search of temporal dependence in the activity of the investigated cells, as final discrimination of the impulses of dependently acting neuronal pairs occurs at the level of the crosscorrelation method itself. The step of the analysis under the use of crosscorrelation method is of decisive significance for revealing of direct interconnections between neurones in the cases when these connections are masked on histograms with wide peaks reflecting the influences of common sources, on the recorded cells.     

Physiological properties of sympathetic preganglionic neurones in the thoracic intermediolateral nucleus of the cat

Extracellular spikes were recorded from cell bodies of sympathetic preganglionic neurones in spinal segments T1-T3 of the cat. Each neurone was identified by its antidromic response to electrical stimulation of the sympathetic chain and was found in histological sections to lie within the intermediolateral nucleus. Physiological properties studied in detail included basal activity, spike configuration, and latency of antidromic activation. Also studied, in tests with paired stimuli, were the threshold interstimulus interval evoking two responses, as well as changes in amplitude and latency of the second spike which occurred at intervals near this threshold. Approximately 60% of the units studied were spontaneously active, the rest were silent. Spontaneous activity was characterized by a slow (mean = 3.1 +/- 2.6 (SD) spikes/s), irregular pattern of discharge. With approximately one-third of the cases there was a periodic pattern of discharge in phase with oscillations in blood pressure. This correlation of phasic activity suggests that many of the units studied were involved specifically in cardiovascular function. Silent and spontaneously active units could not be differentiated on the basis of latency of antidromic activation or threshold interstimulus interval; mean latency for the two groups was 7.2 +/- 4.9 ms, mean threshold interval was 6.4 +/- 4.7 ms. Thus, with the exception of basal activity, the physiological properties studied failed to indicate more than a single population of neurones. These results therefore suggest that the sympathetic preganglionic neurones in the intermediolateral nucleus subserving varied autonomic functions share overlapping physiological properties, and that functional differentiation of these neurones may be based on differences in synaptic inputs.     

Organization of the sensory input of command neurons

Dynamics of habituation of synaptic responses to tactile stimulation of the snail skin was used as a criterion for defining organization of the receptive field of an escape behaviour command neurone. It was shown that every command neurone had its own specific nonhabituating area of the receptive field while the size of the field was common to all command neurones - it comprised the whole skin surface. The receptive field of a command neurone system is not homogeneous in structure. Areas corresponding to ecologically significant regions can be singled out by the maximal response amplitude and low rate of habituation.     

Ca2+-dependent depolarization and burst firing of rat CA1 pyramidal neurones induced by N-methyl-D-aspartic acid and quinolinic acid: antagonism by 2-amino-5-phosphonovaleric and kynurenic acids

The excitatory effects of microiontophoretically applied quisqualic (QUIS), N-methyl-D-aspartic (NMDA), and quinolinic (QUIN) acids were investigated using intracellular recording from CAl pyramidal neurones in slices of rat hippocampus. QUIS evoked only simple action potentials superimposed upon a depolarization which attained a clear plateau. When this level had been reached, increased ejecting currents did not produce further depolarization. By contrast, with low currents NMDA and QUIN elicited small membrane depolarizations which triggered bursts of action potentials superimposed upon rhythmically occurring depolarizing shifts. Larger currents caused depolarization which if sufficiently large completely blocked spike activity. Tetrodotoxin (TTX) prevented the spikes evoked by QUIS and the bursts of action potentials seen with NMDA and QUIN, and the rhythmic depolarizing shifts then appeared as broad spikes of up to 50 mV in amplitude. These and the underlying membrane depolarization were blocked by Co2+, by the NMDA antagonist D(-)-2-amino-5-phosphonovaleric acid (DAPV), and by kynurenic acid (KYNU). It thus appears that the depolarization and burst firing of rat CAl pyramidal neurones elicited by NMDA and QUIN are Ca2+ dependent while the actions of QUIS are not.     

Relationships between amplitudes and kinetics of rapid cytosolic free calcium fluctuations in GH4C1 rat pituitary cells: roles for diffusion and calcium-induced calcium release.

We have examined statistical relationships between the amplitudes and the kinetics (rise times, fall times, and decay constants) of cytosolic free calcium fluctuations (spikes) in a population of 353 individual GH4C1 rat pituitary cells. The fast falling phase was approximated by a single exponential decay, and the decay time constant, tau, increased linearly with spike amplitude in 80% of the cells studied. The slope of the tau versus amplitude plot for each cell was inversely related to the cell's mean spike amplitude. Thus, some process responsible for prolonging the decay phase of spikes appeared to operate strongly in cells with spikes of low amplitude, but to become less prominent in cells with high amplitude spikes. Mean tau correlated more strongly with mean rise and fall times than with mean spike amplitude, indicating that the kinetic properties of spikes were not tightly coupled to spike amplitude. These findings are consistent with a model wherein the rise phase corresponds to entry of extracellular calcium via L-type calcium channels into localized sub-plasmalemmal domains, followed by diffusion of subplasmalemmal calcium into the cell interior; and the falling phase corresponds to further calcium diffusion combined with activation of cytoplasmic calcium-induced calcium release, which prolongs the falling phase.     

Temporal organization of interneuronal relations in the cerebral cortex of the cat in relation to the level of alimentary motivation

By means of records of multicellular activity, interneuronal relations and their modifications in two cortical zones (Visual and motor) were studied in cats at different levels of alimentary motivation. For quantitative evaluation of interneuronal relations the statistic method of cross-correlation analysis of impulse trains was used in determining the probability of the appearance of the discharge of one neurone after the impulse of the other one. For groups of neurones in both investigated cortical areas, three-neurones microsystems were singled out and their activity was analyzed by temporal parameters of interaction between neurones at the interval of 120 ms, both within one microarea (intraanalyzer connections) and between microareas of two cortical zones. The correlation of temporal parameters of interneuronal connections (temporal delays in the activity of neuronal pairs) changed depending on spatial localization of neurones and functional condition of the animals. The existence is suggested of "informational" (1-30 ms) and "motivational" (90-120 ms) values of interneuronal relations for interanalyser connections.     

Function of different medullary neurons in respiration]

1. We have studied the activity of 162 medullary respiratory neurones in the "encephale isole bas" cat. These neurones were classed into three groups : bulbospinal inspiratory (NBSI : 39) or expiratory (NBSE : 15) neurones whose axons enter the spinal cord ; inspiratory or expiratory laryngeal motoneurones (MLI : 17; MLE : 10) antidromically activated by vagus nerve stimulation ; propriobulbar inspiratory (NPBI : 59) or expiratory (NPBE : 22) neurones whose axons lie perhaps entirely within the medulla. 2. Correlation coefficients between number of spikes delivered in each burst and the duration of the corresponding respiratory phase (inspiration for NBSI, MLI, NPBI ; expiration for NBSE, MLE, NPBE) have been calculated for each neurone. 3. The activity of most of the NBSI and MLI is significantly correlated with the duration of the inspiration. These two groups of neurones are probably homogenous. 4. On the basis of this correlation test, NPBI do not constitute an homogeneous population ; 50% of NPBI are not significantly correlated. The same results are obtained if correlations are calculated between the number of spikes delivered and the amplitude of integrated phrenic nerve acitivty. According to the discharge pattern and correlation test, we can consider three groups of NPBI : early recruited neurones with decreasing frequency and non significantly correlated activity (23,7%); early and late neurones with increasing frequency and significantly correlated activity (32,2%); early and late neurones with increasing frequency and non significantly correlated acitivty (44,1%). 5. The activity of most of the NBSE and NPBE with increasing frequency is significantly correlated with the duration of the expiration. Among the MLE and NPBE with a decreasing frequency, a great number of neurones are not significantly correlated. 6. The functional significantion of the different neuronal types is discussed from these correlation tests and from the pattern of activity and axonal pathways.     

Adrenal versus nonadrenal sympathetic preganglionic neurones in the lower thoracic intermediolateral nucleus of the cat: physiological properties

Adrenal and nonadrenal sympathetic preganglionic neurones (SPNs) in the intermediolateral nucleus of spinal segments T8-T10 in the cat were compared according to a number of physiological properties. An SPN was classified as "adrenal" (n = 37) if it could be antidromically activated by electrical stimulation of the adrenal medulla. An SPN that could not be activated from the adrenal medulla yet could be antidromically activated by electrical stimulation of the greater splanchnic nerve was classified as "nonadrenal" (n = 123). Approximately 50% of adrenal SPNs (17 out of 37) were activated antidromically by stimulation of both the greater splanchnic nerve and adrenal medulla, suggesting that these neurones projected to the adrenal medulla via the greater splanchnic nerve, with the other adrenal SPNs taking a different route. The mean conduction velocities of adrenal (6.7 +/- 1.8 (SD) m/s) and nonadrenal (6.7 +/- 1.5 m/s) sympathetic preganglionic axons were similar. Over 80% of adrenal (31 out of 37) and nonadrenal (104 out of 116) SPNs were spontaneously active. The two types of neurone were indistinguishable in terms of the rates and patterns of discharge. Adrenal SPNs discharged with a mean rate of 1.4 +/- 1.1 spikes/s, and nonadrenal SPNs discharged with a mean rate of 1.8 +/- 1.4 spikes/s. With both types of SPN, the pattern of spontaneous activity was either irregular or phasic. With the latter pattern, periodic bursts of discharge were at the same frequency as oscillations in arterial pressure, frequency of ventilation, or phrenic nerve discharge. These data suggest that adrenal and nonadrenal sympathetic preganglionic neurones in the intermediolateral nucleus in caudal thoracic segments share a number of common physiological properties.     

An analysis of the bursting behaviour of the Aplysia R15 neurone during exposure to normoxia and hypoxia with and without external calcium present

Membrane potentials (EM), interburst intervals (IBI), burst durations (BD), the numbers of spikes within a burst, and the amplitudes of the burst pacemaker potentials (BPP) were measured in two groups (N = 7 per group) of R15 neurones under conditions of 20, 10 and 5% oxygen and under nitrogen equilibration in suffusates with either Ca2+ (10 mM) or Mg2+ (10 mM) present (Groups I and II). Under normal extracellular Ca2+ conditions, EM and the amplitude of the BPP for Group I R15 neurones increased progressively during hypoxia and reoxygenation. In the absence of external calcium, the normal bursting pattern of Group II R15 neurones was interrupted. No consistent relationships were observed among BD, IBI, and the number of spikes per burst with respect to EM or BPP. Hypoxia may alter the resting permeability of R15 to potassium as well as having ephaptic effects.     

The characteristics of the formation of spontaneous neuronal activity in the trigeminal sensory nuclei of surviving slices of rat brain stem in postnatal ontogeny]

An attempt was made to characterize the development of neurones of sensory trigeminal nuclei--basic structure of sensory provision of alimentary behaviour at late stages of postnatal ontogenesis. The method of the brain-stem slices of rat pups [correction of ratlings] aged 2.4 and 8 weeks was applied. An increase with the age was shown of the number of neurones with spontaneous activity (44%-2 weeks; 69%-8 weeks), growth of discharges frequency, appearance of cells population with high-frequency spontaneous activity by the fourth week and an increase of such neurones number by the eighth week. Three types of background-active neurones were singled out: episodic, continuous and group; the dynamics of correlations change of these types with the age was shown. No significant changes of rest potential with the age were found, though there was a tendency to its increase between the 2-nd and 8-th weeks of postnatal development.     

Electrophysiological Actions of Oxytocin on the Rabbit Myometrium

The electrical activities of myometrial cells of the pregnant rabbit uterus have been studied by means of sucrose-gap and intracellular micro-electrode recording techniques. The resting potential of the myometrial cell was about -50 mv, and it is unaffected by the duration of pregnancy or placental attachment. Action potentials of the myometrium, although dependent on external Na⁺, were not always of the regenerative type; preparations from nonparturient uteri often produce mainly small spikes. The mean spike amplitude was 35 mv, rising at a mean maximum rate of 3 v/sec. Oxytocin, in concentrations less than 500 µU/ml, increased the mean spike amplitude to 48 mv and the mean maximum rate of rise to 7 v/sec, without affecting the resting potential. The relation between membrane potential and dV/dt of the spike was steepened by oxytocin, suggesting that oxytocin increased the number of normally sparse sodium gates in the myometrial membrane. By this action, oxytocin is believed to increase the probability of successful regenerative spikes and thereby initiate electrical activity in quiescent preparations, increase the frequency of burst discharges, the number of spikes in each burst, and the amplitude of spikes in individual cells.     

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.     

The dependence of the neuronal reactions of the sensorimotor cortex to a simultaneous complex stimulus on the level of the differentiation of its components]

On alert animals the change was studied of the neuronal activity of the sensorimotor cortical area of cats brain in dependence on the level of differentiation of the components of simultaneous heteromodal complex stimulus. According to the character of this dependence and a number of other parameters two groups of neurones were singled out in the sensorimotor cortex. It was shown that parameters of reactions of all recorded neurones of the sensorimotor cortex to the positive conditioned signal were the first established after consolidation of the animal conditioned motor activity. In the course of elaboration following parameters changed: expressiveness, intensity, duration and value of latency. Reactions of neurones of both groups to the inhibitory stimuli were stabilized only after consolidation of the habit of differentiation. Responses of the first group neurones changed only by the pattern of discharge, while the responses of the second group neurones could change by expressiveness of response, its sign, duration and value of latency. Oscillations of the differentiation level after finishing of the elaboration of inhibitory conditioned reactions affected only the responses of the second group neurones to complex components.     

Effect of electric stimulation of cortical portions of the limbic system on the activity of neurons of the anterior thalamic nuclei in the rabbit

Effects of electrical stimulation of the subiculum (SB) and posterior limbic cortex (PLC) were studied extracellularly in the anteroventral (AV) and anterodorsal (AD) limbic thalamic nuclei of awake chronic rabbits. Stimulation of SB and PLC evoked in some AV neurones discharges of 1-2 spikes. Gradual potentiation and low frequency of following (up to 10-15 Hz) were characteristic of these responses. Activity of the majority of AV cells was suppressed by stimulation with appearance of inactivation bursts, "neuronal spindles" and modulation on delta-frequencies. Spike responses were evoked by SB and (rarely) by PLC stimulation only in a certain class of AD neurones which tentatively are regarded as relay cells. The neurones with high-frequency, low-amplitude discharges (putative inhibitory interneurones) reacted to stimulation of PLC and to a lesser extent of SB by prolonged series of spikes (150 ms--2s). Stimulation of PLC exerted prolonged influence upon neuronal responses to sensory stimuli.     

A functional statistical analysis of the action potentials in the brain multineuronal activity of waking cats

In the present work a method is substantiated of the correction of singled out impulses series by identification of parameters of neurones discharges (PD) during a long period of recording (up to 120 days) of the neuronal activity by means of chronically implanted nichrome semimicroelectrode in different brain part of alert cats.