Background impulse activity of neurons of the fastigial cerebellar nucleus of intact and labyrinthectomized rats under conditions of vibration

In acute experiments on nembutal-anesthetized (40 mg/kg, i.p.) albino rats, we recorded extracellularly and analyzed the background impulse activity (BIA) of neurons of the fastigial nucleus of the cerebellum. Experiments were carried out on intact and labyrinthectomized rats in the norm and after long-lasting (up to 15 days) influence of general vertical vibration (60 Hz, 0.4 mm, 2-h-long everyday sessions). Distributions of the neurons according to the level of regularity of BIA, dynamics of spike trains, pattern of histograms of interspike intervals (ISIs), and different frequency ranges of BIA were plotted; the mean frequency of this activity and the coefficient of variation of ISIs were also calculated. Possible mechanisms of the effects of long-lasting vibration of different durations on the BIA generated by neurons of the fastigial cerebellar nucleus in intact animals and after switching off of labyrinth afferent inputs are discussed. Neirofiziologiya/Neurophysiology, Vol. 38, No. 1, pp. 32–39, January–February, 2006.     

Modifications of neuronal activity in the rat hypothalamic supraoptic nucleus after long-lasting vibrational stimulation

We analyzed the background impulse activity (BIA) generated by neurons of the rat hypothalamic supraoptic nucleus in the norm and under conditions of long-lasting vibrational stimulation (exposure 5, 10, or 15 days). Distributions of neurons by the level of regularity, dynamics of discharge trains, form of histograms of interspike intervals (ISIs), as well as distributions of neurons by the BIA frequency ranges, were studied. We also calculated the mean frequency of impulsation of the neurons under study and the coefficient of variation of ISIs. After vibrational influences, we found modifications of both the internal structure of the recorded spike trains and the mean frequency of impulsation within the entire studied group and different frequency subgroups. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 224–230, May–June, 2006.     

Effects of Immobilization Stress on the Background Impulse Activity of Locus Coeruleus Neurons

We studied in rats changes in the impulse background activity (BA) of locus coeruleus (LC) neurons after short- and long-term immobilization stress; distributions of LC neurons by the level of regularity of their BA, dynamics of spike trains, and pattern of histograms of interspike intervals (ISI) were taken into account. We also calculated the means of the main BA statistical indices. Both short- and long-lasting immobilizations resulted in drops in the mean frequency of background discharges of LC neurons to about half of the initial value. Two-hour-long immobilization evoked statistically significant shifts in the distribution of LC neurons by the level of regularity of their BA, while after longer (15 h) immobilization this distribution nearly returned to the initial pattern. Short-lasting immobilization exerted no significant effect on the dynamic characteristics of BA; statistically significant changes in this respect developed only after longer stress. After 15-h-long immobilization, we also observed a noticeable increase in the number of neurons with polymodal ISI distributions. Therefore, stress results in significant modifications of the temporal parameters of the BA of LC neurons; characteristics of the BA of these neurons should be considered neuronal correlates of the stress state.     

Analysis of the Neuronal Background Impulse Activity in the Rat Locus Coeruleus

Using several techniques of statistical analysis, we studied in detail the extracellularly recorded background impulse activity (BA) of neuronal elements of the rat locus coeruleus (LC). Impulse trains generated by most LC neurons were stationary and demonstrated different levels of regularity; a nonstationary type of BA was observed in 17% of the neurons under study. Statistical parameters of the BA generated by LC neurons showed a wide variability. Distributions of the BA interspike intervals (ISI) of most LC neurons were characterized by more or less expressed bimodality or polymodality. Serial correlation analysis of the ISI durations both in stationary and nonstationary spike trains allowed us to differentiate five main types of the dynamics of ISI successions in the BA of LC neurons.     

Background activity of neurons of the supraoptic hypothalamic nucleus in rats under conditions of vibrational stimulation and electromagnetic extrahigh-frequency irradiation

We analyzed background impulse activity of neurons of the supraoptic nucleus of the rat hypothalamus in the course of 15-day-long isolated action of generalized vibrational stimulation and combination of such stimulation with irradiation of the animal’s head with low-intensity extrahigh-frequency (EHF, millimeter-range) electromagmetic waves. The distributions of the neurons by the level of regularity and dynamics of spike trains, separate frequency ranges of impulsation, and pattern of interspike interval (ISI) histograms were estimated. We also calculated the mean frequency of discharges and coefficient of variation of ISIs. A trend toward decreases in the deviations of some parameters of neuronal spike activity generated by supraoptic neurons, which were evident within early time intervals of isolated action of vibration (5 to 10 days), was observed under the influence of EHF electromagnetic irradiation; thus, the latter factor probably exerts a sedative effect. Neirofiziologiya/Neurophysiology, Vol. 39, No. 6, pp. 433–442, November–December, 2007.     

Structure of Neuronal Impulse Trains of the Rat Inferior Olive under Conditions of Long-Lasting Vibrational Influence

In acute experiments on albino rats anesthetized with Nembutal (40 mg/kg, i.p.), we recorded the background impulse activity (BIA) generated by neurons of the inferior olive in the norm and after 5-, 10-, and 15-daylong vibrational influence (60 Hz, 2 h, daily). We characterized the distributions of neurons according to the regularity of impulse successions, their dynamics, and pattern of histograms of interspike intervals (ISIs); we also calculated the mean frequency of impulsation and the coefficient of variation of ISIs. It was demonstrated that the most significant shifts of the characteristics of BIA generated by neurons of the inferior olive were formed within the first 10 days of the vibrational influence. These shifts were observed mainly in the mean discharge frequency (increased within the initial period) and, to a lesser extent, in the intrinsic structure of impulse trains. Such shifts in the background activity of the inferior olive caused by long-lasting vibrational influence result, perhaps, from intensification of the influences of excitatory cerebellar/mesodiencephalic inputs to olivary neurons within the early periods of action of the above factor and prevalence of GABAergic influences within the later periods. It seems possible that, under such conditions, the characteristics of electrical synapses of the olivary neurons are also subjected to modification. Neirofiziologiya/Neurophysiology, Vol. 40, No. 4, pp. 340–347, July–August, 2008.     

Comparative analysis of spontaneous unit activity of the cerebellum fastigial nucleus' neurons in different periods of vibration influence

In conditions of acute experiment on white rats anaesthetized with Nembutal (40 mg/kg, interperitonially) recording and analysis of spontaneous impulse activity of the fastigial nucleus' neurons in norm and after 5, 10 and 15 days of vibration influence on the organism were carried out. Distribution of the neurons was evaluated by the dynamics of neuronal current flow and the modality of the interspike interval hystograms, as well as the statistical parameters: the average discharge frequency and the coefficient of the interspike interval variation. It is shown that more significant changes in neuronal activity of fastigial nucleus cells are formed during the first 10 days of vibration influence. On the 15th day, there was a tendency towards return to control levels of the parameters under study.     

Use of the principles of computer statistical analysis for investigating the background impulse activity of neurons

A program for complex statistical analysis of the background impulse activity of neurons on a computer is proposed. The program includes: determination of the portion of the recording having a stable statistical structure; calculation of histograms of the probability density function of the interspike intervals (ISI) and statistical indexes related with them; correlation-spectral analysis of the ISI sequence; correlation-spectral analysis of the instants of appearance of impulses (from the frequency graph and graph of the function of recovery of impulse activity); and determination of the type and degree of relation of the lengths of adjacent ISI's and entropy analysis of this connection. A method is described for determining the portion of burst and group activity of the investigated neuron in the recording. The effectiveness of using the proposed program was checked by analyzing the background activity of pyramidal cells of the cat cortex. An analysis of neurons equal in frequency of background activity and rate of conduction of impulses in axons showed that the differences in the internal statistical structure of their impulses are very substantial.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 587–600, November–December, 1970.     

Background impulse activity of neurons of the fastigial nucleus in the rat cerebellum

Background impulse activity (BIA) of neuronal elements of the fastigial nucleus (FN) of rat cerebellum were investigated for the first time with the aid of various methods of statistical analysis. A clear predominance of stationary impulse flows (IFs) was discovered, along with irregularities in such flows, variously expressed and including a significant number of realizations of a regular component of impulse activity. Nonstationary IFs constituted a special variety of BIA; they were found in 15% of the total number of neurons investigated. Serial correlation analysis of the durations of interspike intervals (ISIs), both of stationary and nonstationary IFs, allowed us to identify six main varieties of ISI dynamics in the BIA of neurons of the fastigial nucleus. The patterns of recorded IFs and variations in IFs can serve as an adequate indices of the state of cellular activity during intracellular recording from cells of the central nervous system.L. A. Orbeli Institute of Physiology, Armenian Academy of Sciences, Yerevan. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 441–450, July–August, 1991.     

Modulation of Inhibitory Synaptic Transmission in the Cat Motor Cortex Related to Realization of an Operant Reflex Evoked by a Complex of Stimuli

In non-anesthetized cats, we examined the effects of iontophoretic microinjections of GABA, a blocker of GABAergic synaptic transmission, and modulators of noradrenergic transmission on impulse activity (IA) generated by motor cortex neurons in the course of realization of an operant motor reflex to the action of a complex of stimuli (warning and imperative ones). We tried to elucidate the role of different membrane receptors in modulation of spiking of cortical neurons. Microiontophoretic applications of GABA and noradrenaline resulted in decreases in the frequency of background IA of cortical neurons and suppression of their reactions related to realization of the operant reflex. The use of selective adrenoactive substances showed that applications of an α1 agonist, Mezaton, suppressed background spiking and impulsation generated within an interspike interval and in the course of the movement. An α2 blocker, yohimbine, exerted an opposite effect; the neuronal IA was intensified within the background period and other examined time intervals. There are reasons to believe that noradrenergic modulation of IA of cortical neurons is realized via direct effects on pyramidal neurons and also indirectly, through changes in the activity of inhibitory cortical interneurons.     

Background neuronal activity in thenucleus supraopticus and its modifications under the influence of parathyroid hormone

In experiments on anesthetized cats, we found that i. v. injection of 5.0 U/kg of parathyroid hormone (PTH) results in modifications of the statistical parameters of the neuronal impulse activity in thenucleus supraopticus (SO) of the hypothalamus. Sliding frequency graphs, histograms of interspike intervals, autocorrelograms, and serial correlation coefficients were plotted and calculated before and after PTH injections; their comparison demonstrates that the hormone significantly modulates the temporal organization of spike trains generated by the neurons of this nucleus. We observed that PTH mostly activated SO neurons and diminished the level of spike grouping in their activity. The effect of PTH to a certain level depended on the initial frequency of background activity: an increase in the spiking frequency was typical of primarily dominating “low-frequency” neurons, while “high-frequency” units were mostly inhibited. The possible mechanisms of the observed modifications are discussed.     

Reflection of the plastic properties of monosynaptically interconnected neurons in the statistical characteristics of their spike activity

By mathematical and biomathematical methods of neuronal interaction modelling, changes were studied of cross-correlation histograms (CCH) of impulse flows and of average interimpulse intervals of monosynaptically interconnected neurones, at changes of efficiency of forward and backward connections, of excitability of neurones and of summate action on them of independent random afferent synaptic inflows. It is shown, that a single sign of efficiency increase of monosynaptic excitatory or inhibitory connection between neurones (amplitude increase of the corresponding postsynaptic potential) consists in amplitude increase of the main peak or trough the rated CCH of their impulse flows, followed by a decrease of average interspike intervals of both neurones.     

Asymmetry of Characteristics of the Background Activity of Neurons of the Medial Vestibular Nucleus in Rats After Long-Term Vibration

Using computer analysis, we compared characteristics of the impulse background activity (BA) generated by neurons in the right and left medial vestibular nuclei (MVN) of the rats under control conditions and on the 5th, 10th, and 15th day with everyday 2-h-long sessions of vibrational stimulation. In the control group, the BA frequency generated by left-side MVN neurons was, on average, higher than that in the right MVN (23.6 ± 1.5 and 16.6 ± 1.7 sec^-1, respectively); other main characteristics of the BA demonstrated no significant internuclear differences. Vibrational influences of different durations induced complex significant laterally specific modifications of the level of regularity and dynamic indices of BA generated by neurons of the right and left MVN, of proportions of the cells with different types of distribution of interspike intervals (ISI), and of coefficients of variations of ISI. The mean frequency of background spiking in the right MVN increased about twofold (to 31.6 ± 2.2 sec^-1) after 10 days with vibration sessions, but dropped on the 15th day to 20.6 ± 1.7 sec^-1. In the left MVN, the mean BA frequency monotonically decreased, to 11.6 ± 1.0 sec^-1 after 15 days with vibration sessions. Therefore, chronic vibrational stimulation results in differential shifts of the characteristics of the BA generated by neurons of two MVN and in the formation of a new significantly asymmetrical pattern of such activity. Possible reasons for lateral asymmetry of the impulsation of MVN neurons and modifications of this asymmetry after long-term vibrational influences are discussed. We suppose that such an asymmetry can be one of the factors responsible for the development of motor and autonomic manifestations of vibration-induced motion sickness.     

Spontaneous activity of auditory cortical neurons of waking cats at rest and during defensive conditioning

The results of a computerized statistical analysis of 366 realizations of spontaneous spike activity of 181 neurons in the primary auditory cortex (area 50) of waking cats at rest and during defensive conditioning are described. In both situations the parameters of spontaneous activity of most neurons differed from those of a random flow. Conditioning led, on the one hand, to a stable increase in the frequency of spontaneous activity in intertrial periods and, on the other hand, judging from changes in the mean firing rate, the coefficients of variation of the length of the interspike intervals, the histograms of their distribution, and also the increase in the number of neurons with different forms of correlation between interspike intervals, to an increase in its stability (degree of organization).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 227–238, May–June, 1978.     

Effects of coagulation of thelocus coeruleus and pontine raphe nuclei on the background activity recorded from the rat cerebellar fastigial nucleus neurons

Simultaneous or separate coagulation of thelocus coeruleus (LC) and the pontine raphe nucleus (PRN) results in a significant increase of irregular-type background activity in the cerebellar fastigial nucleus neurons. There are also considerable changes in the dynamics of impulse sequences, in particular, the number of neurons with random interpulse intervals markedly increases. Destruction of theLC and/or PRN is followed by a marked drop in the mean frequency of discharges in the neurons of the fastigial nucleus.Neirofiziologiya/Neurophysiology, Vol. 26, No. 6, pp. 437–442, November–December, 1994.     

The background and evoked neuronal impulse activity of embryonic neurotransplant of somatosensory brain cortex in rats

The investigation was intended for studying the character of the background and evoked impulse activity of embryonic neurotransplant neurons 4 months after homotopical allotransplantation into the barrel field of somatosensory recipient's brain cortex of the rat. It is established, that the current average frequency of background impulse activity of transplant neurons is reduced in comparison with one of the control rats. It is shown that the evoked impulse activity of neurotransplant develops with the long latency than in somatosensory cortex of the control animals. Thus in patterns of the evoked activity of neurotransplant cells reactions, characteristic for the neurons of barrel field somatosensory recipient's cortex of control rats are registered: an increase of frequency of pulses' generating, or alternating of the activation and reduction periods of impulse frequency with its subsequent regeneration up to a pristine level.     

Changes in electric activity of neurons of dorsal raphe nuclei in the development of generator of pathologically enhanced excitation in the nociceptive system

In the experiments on rats it was proved by the method of extracellular registration of impulse neuron activity of dorsal raphe nucleus, that the formation of generator of pathologically enhanced excitation (GPEE) in nociceptive structures of spinal brain underlying the pain syndrome of spinal origin, results in a change of electric neuron activity of dorsal raphe nucleus. These changes are manifested by growing number of background nucleus neurons, the increase of middle frequency of discharges, and assuming pack character of impulse activity. These changes are greater marked in a ventral nucleus part, than in a dorsal one, which is evident of the activation of this antinociceptive system structure. The changes of electric activity of dorsal raphe neurons are stable for a long time after GPEE is formed in nociceptive system, and participate in suppression of GPEE and corresponding pain syndrome.     

Interspike background activity in extracelullarly recorded Purkinje neurons: spectral analysis

The aim of this study was to investigate the spectral characteristics of Purkinje cell interspike background activity caused by the occurrence of particular action potentials or by electrically induced enhancement of cerebellar inhibitory and excitatory input drive. Spontaneously active Purkinje neurons were extracellularly recorded in anesthetized rats before and after cessation of stimulation from the inferior olive (10) or locus coeruleus (LC). After A/D conversion (30 kHz), direct spectral analysis of extracted interspike background activity was done. Our results have shown that, in contrast to simple spikes, the occurrence of complex spikes induces changes in the spectra of interspike background activity. The different spectral changes of interspike background activity induced by LC and 10 stimulation also indicated the importance of this extracellularly recorded phenomenon.     

The dependence of impulse propagation speed on firing frequency, dispersion, for the Hodgkin-Huxley model.

Propagation speed of an impulse is influenced by previous activity. A pulse following its predecessor too closely may travel more slowly than a solitary pulse. In contrast, for some range of interspike intervals, a pulse may travel faster than normal because of a possible superexcitable phase of its predecessor's wake. Thus, in general, pulse speeds and interspike intervals will not remain constant during propagation. We consider these issues for the Hodgkin-Huxley cable equations. First, the relation between speed and frequency or interspike interval, the dispersion relation, is computed for particular solutions, steadily propagating periodic wave trains. For each frequency, omega, below some maximum frequency, omega max, we find two such solutions, one fast and one slow. The latter are likely unstable as a computational example illustrates. The solitary pulse is obtained in the limit as omega tends to zero. At high frequency, speed drops significantly below the solitary pulse speed; for 6.3 degrees C, the drop at omega max is greater than 60%. For an intermediate range of frequencies, supernormal speeds are found and these are correlated with oscillatory swings in sub- and superexcitability in the return to rest of an impulse. Qualitative consequences of the dispersion relation are illustrated with several different computed pulse train responses of the full cable equations for repetitively applied current pulses. Moreover, changes in pulse speed and interspike interval during propagation are predicted quantitatively by a simple kinematic approximation which applies the dispersion relation, instantaneously, to individual pulses. One example shows how interspike time intervals can be distorted during propagation from a ratio of 2:1 at input to 6:5 at a distance of 6.5 cm.     

Electrical processes involved in the encoding of nerve impulses

A mechanism for impulse encoding is advanced for those neurones whose impulse trigger zone membrane is more excitable than the general axonal membrane. Electrical communication between an electrotonically small patch of highly excitable membrane and neighboring membrane places the control of membrane potential — in varying degree — to the larger membrane area throughout the interspike intervals. That control is relinquished to the trigger membrane near the time of action potential initiation in a natural fashion. Model calculations demonstrate that this mechanism can lead to a dramatic lowering of the minimum stable firing frequency of tonic neurons, and, additionally influence the shape of the stimulus —versus — impulse frequency curve. The results are compared with the behavior of the slowly adapting stretch receptor neuron of the crayfish.Research supported by NSF grant BNS 77-22532 and Public Health Service Grant EY 00293. Computer facilities were made available by the Air Force Office of Scientific Research (AFOSR-1221) and by the University of Minnesota Computer Center