Hippocampal electrical activity during development and following the establishment of a dominance-subordination relationship in rabbits

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Abstract
Hippocampal electrical activity can be modulated by social behaviour. The aim of the present experiment was to study the long-lasting effects of social interactions on hippocampal EEG. Two male rabbits, implanted with chronic nichrome electrodes in the hippocampus, were introduced to an open air, seminatural environment and their spontaneous behaviour was studied for 3 days. In this period, one of them exhibited dominant behaviour and the other signs of subordination. Hippocampal electrical activity was recorded by two high-power telemetry devices, one for each rabbit. The behaviour, recorded by video cameras, and neural activity of both rabbits were videotaped and then analyzed. This method allowed simultaneous comparisons between the electrical profiles of dominant-type and subordinate-type behavioural elements. Results show that typical hippocampal electrical patterns can be ascribed to dominant and subordinate subjects. Behavioural aspects of dominance were observed in one of the two animals early in the observations and were confirmed at the end of the experiment after the introduction of an intruder (a male rabbit). The hippocampal electrical activity of the dominant animal showed an increase of frequency which was evident after the first or second experimental session. Rhythmicity of hippocampal EEG increased in the dominant animals. These electrical variations were particularly evident during behavioural elements such as quiet immobility, exploration and interactive behaviour.