The effect of amygdaloid ablation or stimulation on plasma corticosterone levels in the male rat

Data indicate that in the male rat the amygdala is capable of influencing ACTH secretion, and the finding that pituitary-adrenal function was not compromised by either selective or extensive amygdaloid ablation suggests that the amygdala was not essential for pituitaries' function as this function was assessed.

Abstract

Participation of the amygdaloid complex in pituitary-adrenal function was assessed by measuring plasma corticosterone levels after a variety of ablative or stimulatory procedures in male rats. Transection of the stria terminalis, ablation of the basolateral amygdalopiriform region or subtotal amygdalectomy did not alter a.m. or p.m. non-stress plasma corticosterone levels. Likewise, stress-induced increments in plasma corticosterone concentrations in experimental rats were not different from those in controls after 3 min exposure to ether vapor or immobilization in a supine position. As a corollary to the ablation studies, rats bearing chronically implanted electrodes were subjected to sham or electrical stimulation. In non-anesthetized (freely moving) rats electrical stimulation of the corticomedial amygdala, and basolateral amygdala, dorsal hippocampus and arcuate nucleus resulted in plasma corticosterone levels significantly (P < 0.05) greater than from those in sham stimulated controls. In contrast, in pentobarbital anesthetized rats plasma corticosterone concentrations in the amygdaloid and hippocampal stimulated animals were not different from those of sham stimulated rats; only stimulation of the arcuate nucleus produced plasma corticosterone levels greater (P < 0.05) than those in sham stimulated rats. These data indicate that in the male rat the amygdala is capable of influencing ACTH secretion. However, the finding that pituitary-adrenal function was not compromised by either selective or extensive amygdaloid ablation suggests that the amygdala is not essential for pituitary-adrenal function as we assessed this function.