ALTERATION OF RHYTHMIC ACTIVITY OF THE HIPPOCAMPUS AND ENTORHINAL CORTEX IN KAINIC ACID-INDUCED NEUROTOXICITY IN FREE MOVING RATS

The hippocampus and the medial entorhinal cortex (MEC) interact through bilateral connections and play an important role in the processing, storage and reproduction of information. Data from healthy animals indicate that theta and gamma oscillations are critical activity necessary for the interaction of the hippocampus and MEC in signal processing. At the same time, these structures are one of the most vulnerable areas of the brain during excitotoxic events leading to damage and death of neurons. In this work, excitotoxicity was provoked by systemic administration of kainic acid (KA), which causes the development of epileptic status. In healthy rats with saline and rats injected with KA, local field potentials were recorded simultaneously in the CA1 field of the hippocampus and MEC during open-field research behavior. The distinct theta (4-10 Hz), slow gamma (25-50 Hz) and fast gamma rhythms (55-100 Hz) in the hippocampus and MEC were found in animals of both groups. The movement of healthy animals to the center of the open field was accompanied by an increase in the frequency of the theta rhythm and a decrease in the frequency of the fast gamma rhythm in the hippocampus; in the MEC there was a decrease in the power of the slow gamma rhythm. At the same time, this was not observed in rats with the injection of KA. This group also revealed a violation of the phase-amplitude modulation of the MEC activity by the hippocampal theta rhythm: when animals were moved from the peripheral zones to the center of the open field, the changes in this modulation were significantly less pronounced than in the control. A significant increase in theta coherence between the hippocampus and MEC was found at all animal positions in the open field. Changes in the characteristics of rhythms and hippocampal-entorhinal relationships are possible biomarkers of disturbances in the coding of spatial information and its retrieval from memory, observed as a consequence of status epilepticus often leading to the development of a seizure focus in the temporal brain structures.