Adrenal Stress Responses Following Septal Lesions in the Rat

In order to characterize the effects of septal lesionsupon adrenal stress responses, plasma corticosterone levels were examined 2 days after surgery in normal and sham-operated rats and in rats with septal lesions 0, 5, 15, 30, and 60 min after either 5 sec of handling or 3 min of novel environment at both the crest and trough of the adrenal cycle. Baseline levels and diurnal variations were comparable in lesioned and non-lesioned groups. Non-lesioned rats reacted to stress with an elevation of corticosterone which peaked and leveled off 15 min after the end of stress. Their response was greater following 3 min of novel environment than after 5 sec of handling. 60 min after stress, corticosterone levels had begun to return to baseline levels at trough but not at crest of the adrenal cycle. Rats with a septal lesion had an overall stress-response pattern similar to that observed in non-lesioned animals, but the response latency of septally-lesioned rats was much shorter than that of non-lesioned animals, and their corticosterone levels at 0, 5, and 15 min after stress were greater than those of non-lesioned rats. The mean magnitude of overresponse in rats with septal lesions was greater at trough than at the crest of the cycle. It is concluded that baseline adrenal function is not altered by destruction of the septal nuclei but that septally-lesioned rats have a reduced threshold for adrenal activation which is demonstrated by elevated corticosterone levels during the first 15 min following stimulation and that this increased sensitivity to stimulation is greater at trough than at the crest of the adrenal cycle.