[Detection of c-fos expression in animal brain in a pilocarpine model of temporal lobe epilepsy].

The dynamics of the involvement of different brain structures in a pathological process is very important for decoding the mechanisms of temporal lobe epilepsy. In this work, the experimental model of temporal lobe epilepsy induced by lithium chloride and pilocarpine was used. The method of immunochemical detection of the immediate early gene c-fos was used as an indicator of functioning neurons in the brain. The c-fos expression was determined at different time points (30, 60 and 90 min) after the pilocarpine injection. An increase in the c-fos expression was observed in neuronal populations during the development of the status epilepticus, the time and degree of involvement of different brain structures being different. The expression of c-fos was first observed in the piriform cortex, the olfactory tubercle, thalamic nuclei, lateral habenular nuclei, and the caudate putamen. Then the hippocampus, the septal formation, the amygdala, and basal ganglia were involved in the activation process. In the hypothalamic areas, c-fos expression was observed latest. These data contribute to understanding the mechanisms of temporal lobe epilepsy and searching for the ways of its therapy.

Modulation of the reaction of hippocampal neurons to sensory stimuli by cholinergic substances.

The influences of increasing endogenous acetylcholine (eserine) and its blockade (scopolamine) on the effects of sensory stimuli were analyzed through the extracellular recording of the activity of individual hippocampal neurons of awake rabbits. An increase in the level of acetylcholine, accompanied by the appearance of stable theta rhythm, leads to a substantial decrease in the reactivity of neurons, the suppression, attenuation, and inversion of the majority of inhibitory reactions and of a substantial proportion of activational reactions including on-responses of a specific type. At the same time, a limited group of activational reactions is intensified and extended against the background of eserine. Scopolamine, which blocks theta rhythm, does not change or intensifies inhibitory and some activational reactions, including on-responses. Tonic reactions are shortened; however, their gradual extinction disappears. The effects described are preserved in the hippocampus in the presence of basal undercutting of the septum which eliminates ascending brainstem pathways. These data make it possible to draw the conclusion that, under normal conditions, a new (significant) sensory stimulus elicits in the hippocampus an initial stoppage (reset) of activity with the coordinated triggering of theta rhythm and the passage against this background of signals along the cortical input in a specific phase relationship to it. The period of theta modulation switched on by the signal fosters its recording and the limitation of the passage of subsequent, interfering signals. The septohippocampal influences may thus support the mechanism of selective attention, as a necessary precondition for memory.

Theta modulation of neurons of the hippocampus of the rabbit and its interrelationship with other parameters of spontaneous and evoked activity.

The reliability of the existing functional criteria of the differentiation of pyramidal ("neurons with complex spikes") and inhibitory ("theta neurons") cells of the hippocampus is examined on the basis of a statistical analysis of the spontaneous and evoked activity of neurons of the hippocampus of the awake rabbit. The analysis shows that the parameters of average frequency, the presence of theta modulation of activity, the behavior of the neurons in situations evoking theta rhythm in the EEG of the hippocampus (inhibition or activation during the effect of sensory stimuli), and the character of the influences of stimulation of the medial septal region of the internal connections of the hippocampus do not permit the reliable identification of different types of neurons of the hippocampus in the awake rabbit. The available data on the functional classification of neurons of the hippocampus are discussed in connection with notions regarding their state in situations associated with the generation of theta rhythm.