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A M Karanov

Publications and source records attributed to A M Karanov.

7 recordsLinked to original sources
PubMed1985

Frequency modulation of neuronal theta-bursts in rabbit's septum by low-frequency repetitive stimulation of the afferent pathways.

Activity of the neurons with stable theta-bursts was recorded extracellularly in intact and hippocampectomized septum of unanesthetized chronic rabbits during low-frequency (3-17 Hz) stimulation of horizontal limb of diagonal band or lateral septal nucleus. The stimulation rarely evoked standard oligosynaptic single-spike responses in stable theta-bursting units. Instead, gradual entrainment and phase-locking of the spontaneous theta-cycles occurred. Two types of entrainment were observed: "entrainment by the pause", where interburst interval was reset by the stimuli; and "entrainment by the burst", where bursts were time-locked to the stimuli. Such reorganization of the spontaneous bursts occurred in the narrow frequency range of stimulation (from 4 Hz up to 9-12 Hz), with the best resonance following in the range of "basic" theta frequencies of the awake rabbit (5-6 Hz). With stimulation beyond the theta-range three phenomena occurred: shift of the burst frequencies to higher or lower harmonics of stimulation frequencies; complex interactions of basic background frequency with rhythm of stimulation ("beating"); return to background theta-burst frequency in spite of continuing stimulation ("escape"). The properties of the septal theta-bursting cells as presumable intrinsic bursting pacemakers are discussed.

Afferent Pathways↗
PubMed1985

[Analysis of the background activity of neurons of the anterior (limbic) nuclei of the thalamus in the rabbit].

Background activity recorded extracellularly from three anterior (limbic) nuclei of the thalamus was analyzed in chronic unanesthetized rabbits. The neurons of anteroventral nucleus possessed high mean frequency of discharges and highly differentiated dynamic patterns of activity with "inactivation bursts", modulation in delta- or theta-frequencies and episodic rhythmic discharges 12-14 Hz correlated with EEG-spindles in the posterior cingulate cortex. The activity of anteromedial nucleus neurons was lower and much more uniform; it consisted of alternating randomized spikes and "inactivation bursts". The activity of anterodorsal nucleus neurons was represented mainly by high-frequency grouped discharges with long intergroup intervals.

Action Potentials↗
PubMed1984

[Background activity of neurons of the cortical portions of the limbic system of the rabbit brain].

Background activity recorded extracellularly in cortical limbic areas of unanesthetised rabbits was analyzed by means of a computer. Special attention was payed to the rhythmic components of the activity in theta- and delta-range. Only small proportion of units (5-12%) in various structures, except lateral entorhinal cortex possessed rhythmic modulation in theta-range. Delta-modulation was observed in all investigated areas, but had various characteristics. It was very prominent both in subiculum (45% of units) and in entorhinal cortex (22%). While in subiculum (as in other areas) it consisted of high-frequency short bursts with long interburst intervals, the opposite was typical of entorhinal cortex. Arousing stimuli increased frequency and regularity of theta-bursts and desynchronized delta-activity in majority of structures; in entorhinal cortex they increased intraburst frequency of discharges without influencing frequency or regularity of the bursts.

Animals↗
PubMed1980

Neuronal activity of the septum following various types of deafferentation.

Extracellular recording of neuronal activity of septal nuclei was performed in unanesthetized chronic rabbits in the following conditions: (1) intact septal nuclei; (2) complete interruption of connections with hippocampus; (3) complete basal undercutting of septum. Additional series of records were performed in transversal guinea pig septal slices incubated in vitro. Computer analysis of activity was used. Interruption of hippocampal connections increased the mean frequency of discharges in the lateral septal nucleus 2-fold. Theta-bursts were preserved and the proportion of theta-bursting neurons increased from 28 to 42%. The mean frequency of theta-bursts was slightly augmented (mean 5.4 cps versus 5.2 cps in intact septum). Twenty-six per cent of neurons were characterized by regular, pacemaker-like discharges, while in the normal septum such units were almost completely absent. After septal undercutting the mean frequency of spontaneous activity was increased 2-fold in the medial septal nucleus. Rhythmic bursts were again preserved, the proportion of bursting neurons was close to normal (25%), but the mean frequency of bursts was significantly lower (mean 3.3 cps). Rhythmic activity was extremely regular. Neurons (21%) with pacemaker-like activity were also present. In septal slices neurons possessed relatively high spontaneous activity (mean 10.2/sec). In the majority of units (64%) activity was highly regular. Twenty-two per cent of the units possessed rhythmic bursts in their activity with frequencies of 2.0-5.1 cps. The role of intrinsic septal mechanisms and afferent influences in generation and modulation of theta-bursts is discussed.

Afferent Pathways↗
PubMedDate not supplied

[Frequency modulation of theta volleys of septal neurons during rhythmic oligosynaptic stimulation in the rabbit].

Activity of the neurones with stable theta-bursts was recorded extracellularly in intact and hippocampectomized septum of unanaesthetized chronic rabbits during low-frequency (3-17 Hz) stimulation of horizontal limb of the diagonal band or the lateral septal nucleus. Gradual entrainment and phase-locking of the spontaneous theta-cycles occurred. Two types of entrainment were observed: "entrainment by pause", where interburst interval was reset by the stimuli; and "entrainment by burst", where bursts were time-locked to the stimuli. Such reorganization of the spontaneous bursts occurred in a narrow frequency range of stimulation (from 4 Hz up to 9-12 Hz), with the best resonance following in the range of "basic" theta frequencies of the awake rabbit (5-6 Hz). With stimulation beyond the theta-range three phenomena occurred: shift of the burst frequencies to higher or lower harmonics of stimulation frequencies; complex interactions of basic background frequency with the rhythm of stimulation ("beating"); escape from the influence of the stimuli with return to background theta-burst frequency.

Animals↗
PubMedDate not supplied

[Regulation of the theta activity of septal neurons by cortical and brain stem structures].

Neuronal rhythmic burst activity was recorded extracellularly in the intact septum (34 cells) and in septum deprived of hippocampal connections (100 cells) during electrical stimulation of various neocortical areas, midbrain and pontine reticular formation, and medial forebrain bundle (MFB) in the preoptic area. All structures tested influenced burst production in septal cells. Cortical influences might phasically trigger or regularize theta-activity, but more often they suppressed and desynchronized it. The reticular stimulation tonically increased frequency, regularity, and density of the theta-bursts. MFB influences were similar, but less effective. Increasing the intensity of the stimulating current resulted in a logarithmic increase of theta-burst frequency up to the upper limit of the EEG theta-frequencies (9-10 Hz). Short electrical or sensory stimulation reset the burst activity so that the series of bursts followed each other for several seconds in a stable pattern, which was reproduced by each next application of the same stimulus. Regulation of the theta-rhythm by direct influences upon various types of septal units without hippocampal involvement is discussed.

Animals↗