Implication of the serotoninergic system in the decreased ACTH response to stress after lesion of the amygdaloid central nucleus

1. The present study was designed to ascertain the possible implication of the serotoninergic system and the central amygdaloid nucleus in the control of ACTH secretion in response to immobilization stress.

2. The response to immobilization stress of intact and lesioned animals was studied by monitoring the plasma and pituitary ACTH concentration and the activity of the serotoninergic system within specific hypothalamic and amygdaloid nuclei.

3. Bilateral lesions of the central nucleus of the amygdala significantly decreased the secretion of ACTH in response to immobilization. Moreover, the serotoninergic activity in most of the hypothalamic and in all the amygdaloid nuclei studied was greatly increased. A 60-min immobilization stress prevented this increase in the hypothalamic nuclei but not in the amygdala.

4. These results indicate that the central nucleus of the amygdala participates in the regulation of ACTH secretion in response to immobilization stress. Furthermore, they substantiate the hypothesis of a participation of the serotoninergic system in limbic areas, particularly in nuclei which contain neurons possessing glucocorticoid receptors such as the medial, basomedial and cortical amygdaloid nuclei.