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A N Chepkova

Publications and source records attributed to A N Chepkova.

27 records · Page 2Linked to original sources
PubMed1983

[Effect of enkephalins on the reactivity of 2 hippocampal synaptic systems].

The effects of leu- and metenkephalin administration into the perfusion medium on CA-1 and CA-3 pyramidal cell reactivity to electric stimulation of Shaffer collaterals and mossy fibers, respectively, were investigated on mice hippocampal slice preparations. The reactivity changes were measured by amplitude changes in focal potential, which reflected a synchronous pyramidal cell discharge (population spike, PS). Infusion of 10(-6) M leu- or metenkephalin resulted in a rapid and reversible 200-300% increase in the PS amplitude in CA-1 field of the hippocamp, that was blocked by preliminary administration of 10(-5) M naloxone. An increase in the PS amplitude in CA-3 region was observed as a result of the infusion of much higher enkephalin concentrations (10(-4) M) and did not exceed 50%. The data obtained allow the conclusion that enkephalins enhance the reactivity in the two main intrahippocampal synaptic systems but have a more pronounced effect on CA-1 pyramids.

Animals↗
PubMed1979

["Inhibition of inhibition" in neurons of the cerebral cortex].

Light flashes and single electrical stimuli applied to the nucleus ventro-posterolateralis and to the LGB evoked protracted IPSPs in visual and sensorimotor cortical neurons respectively. High-frequency stimulation of the midbrain RF suppressed these IPSPs which was manifested in a shortening of the inhibitory pause and in a decrease in the amplitude of the IPSPs up to their complete elimination (disinhibition). Activation of noradrenergic pathways by stimuli applied to the locus coeruleus or to the lateral hypothalamus led to the same result. The suppression of cortical IPSPs followed by facilitation of cortical unit firing in response to thalamic or peripheral stimulation seems to be an imprortant mechanism underlying arousal.

Animals↗
PubMedDate not supplied

Effects of deprolorphin, a casomorphin analog, on hippocampal CA1 field potentials in vitro.

The effects of infusion of low concentrations of the synthetic opioid peptide D-Pro4-beta-casomorphin-5(deprolorphin) on electrical field responses in the in vitro hippocampal slice preparation of mice were investigated. Deprolorphin (0.01-10 microM) causes a large enhancement of the population spike (PS) and appearance of additional spikes of CA1 pyramidal cells to Schaffer-commissural stimulation, which were partially antagonized by the opiate receptor antagonist naloxone. It is likely that this analgesic peptide in the hippocampus acts through mu-receptors and neuronal mechanisms already described for morphine and enkephalin analogs.

Animals↗
PubMedDate not supplied

[Synaptic plasticity in learning and memory].

Pavlovian conditioning has been considered as one of the principal experimental approaches to understanding such complex brain functions as learning and memory. Use-dependent alterations in synaptic efficacy are believed to form the basis for these functions. The algorithm of synapse modification proposed by D. Hebb as early as 1949 is the coincident activation of pre- and postsynaptic neurons. The present review considers the evolution of experimental protocols which were used to reveal the manifestations of Hebb-type plasticity in the synaptic inputs to neocortical and hippocampal neurons. Special attention is focused on long-term modifications of synaptic efficacy in the hippocampus as a possible neuronal mechanism of learning and the role of disinhibition in their development. The effects of various neuromodulators on hippocampal long-term potentiation are considered. It is suggested that along with their involvement in disinhibition processes these substances may control the Hebb-type plasticity through intracellular second messenger systems.

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PubMedDate not supplied

[Antidromal action potentials as a manifestation of trace excitation].

The possibility of occurance of action potentials (AP) in neuronal terminals after preliminary excitation of a cortical area was studied in unanaesthetized, non-immobilized rabbits. It was found that a low-frequency subconvulsive stimulation of the sensorimotor cortex may lead to a spontaneous appearance of AP groups that spread antidromically toward the soma of callosal neurones in the opposite hemisphere. Groups of spontaneous antidromic AP were recorded in the cortex after the disappearance of convulsive activity caused by application of penicillin. It is assumed that the observed phenomena reflect a prolonged retention of increased excitability in the terminals of cortical neurones after the end of electrical stimulation or penicillin action.

Action Potentials↗
PubMedDate not supplied

[Changes in the functional characteristic of motor cortex neurons following their rhythmic polarization].

The study was devoted to the effect of rhythmical extracellular activating polarization on spontaneous and evoked (by stimulation of the ventroposterolateral nucleus of the thalamus) unit activity of the motor cortex, preliminarily sensitized by application of an epileptigen (penicillin or strychnine solution). The experiments were carried out on alert unrestrained rabbits. A 3-5 minutes rhythmical polarization of the neurons (0,12, 0, 10 c/s, 200-600 msec pulse duration) resulted in following aftereffects: 1) changes in the mean spike frequency in 58% of neurons; 2) increase of grouping of firing in units with an initial group-type spontaneous activity (21%); 3) assimilation of the polarizing rhythm (10%); 4) facilitation of excitatory phases of thalamically evoked unit responses that occured simultaneously with an increase of mean discharge frequency (18%). The results are discussed from the point of view of the hypothesis of excitatory reverberation in the microsystem of interconnected neurons.

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