EFFECTS OF WHOLE-BODY GAMMA-IRRADIATION ON ACTIVITY OF RABBIT HIPPOCAMPAL NEURONS

The hippocampal cellular activity was recorded by means of microelectrodes in unanesthetized immobilized rabbits, receiving 450 rad of whole-body γ irradiation. A statistical analysis of the data was performed by a computer program developed to process time interval series. A comparison was made between observations obtained in unirradiated and irradiated rabbits. The following results were obtained: After irradiation the hippocampal cellular activity was highly disturbed; The mean discharge rate was clearly slowed down and the variability of interspike intervals was increased; The background activity of some cells was greatly reduced or almost suppressed; The firing patterns of discharge were different from the control. The patterns which revealed a temporal organization of the action potentials in various types of bursts were more rarely observed. On the other hand, the occurrence of spikes without evident temporal organization was the predominant pattern of firing; These changes set in early and continued for the whole recording session (12 hr after the end of irradiation). Because present knowledge in the various related fields is scanty, the interpretation of these results must remain hypothetical.