Effects of medial septal lesions on the hippocampal electrical activity and the orienting response to auditory stimulation in drinking rats

Abstract Medial septal lesions (MSL) abolished hippocampal theta activity and attenuated the overall hippocampal potential level, while frontal cortical lesions (FCL) had no effect on theta rhythm. A decrease in the overall potential level was observed only in some FCL rats. Although spontaneous behavioral patterns, including drinking, face-washing, searching, body movements, awake-and-resting, and slow-wave sleep, were not altered either by MSL or FCL during the 15 min observation, orienting responses to tones, especially searching-type, were reduced during drinking in MSL rats, while no such reductions were observed in FCL and no-lesion control rats. Auditory evoked potentials were not changed either by MSL or FCL. Spontaneous behavioral patterns were not different in FCL rats whether or not the overall hippocampal potential level was decreased.