Hippocampal function and putative corticosterone receptors. Effect of septal lesions

In order to investigate the relation between septohippocampal function and hippocampal corticosterone (B) receptors, discrete septal areas were destroyed by electrolytic lesions; the effects of the lesions on cytosol receptor binding of B in the hippocampus were determined 10 or 30 days after lesioning in male rats adrenalectomized 12 h prior to sacrifice. The septal lesions were also characterized functionally by endocrine, neurophysiological and behavioral parameters in the same group of animals. Hippocampal B receptor activity was increased 30 days after lesioning the lateral septal area. The same lesions impaired the acquisition of a conditioned avoidance response. The increase was not due to a behavioral deficiency per se as lesions in the parafascicular nucleus did impair acquisition behavior without affecting B receptors. There was no change in B receptor activity 30 days after destruction of the medial septal nucleus, although such a lesion completely abolished the hippocampal theta activity measured at 10 days. In another group of animals hippocampal B receptors were not affected at 10 days after any of the lesions, while a transient increase in basal plasma levels of B was noted at that time. It appears that the hippocampal receptor activity for B depends on the integrity of the efferents from the hippocampus and/or the dorsolateral septal B receptor system rather than on the septal afferents to the hippocampus.