Effects of adrenergic and serotonergic agonists in the amygdala on the hypothalamo-pituitary-adrenocortical axis.

The effect of direct administration of adrenergic and serotonergic (5-HT) agonists into the central nucleus of the amygdala (AMG) on the hypothalamo-pituitary-adrenal (HPA) axis have been studied in intact male rats and in animals with 6-hydroxydopamine (6-OHDA) or 5, 7-dihydroxytryptamine (5,7-DHT) neurotoxic lesions in the paraventricular nucleus of the hypothalamus (PVN). In intact animals, the administration of phenylephrine, an alpha1 adrenergic agonist or 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) a 5-HT(1A) agonist caused depletion of median eminence corticotropin releasing hormone and a rise in serum adrenocorticotrophic hormone (ACTH) and corticosterone (CS) levels. Isoproterenol a beta agonist was more effective than phenylephrine and a 5-HT(1B) agonist CP-93, 129 was less effective than 8-OH-DPAT on the adrenocortical activity. The 6-OHDA or 5,7-DHT hypothalamic lesions prevented the stimulatory effects of phenylephrine and 8-OH-DPAT, respectively, which where injected into the AMG, on serum ACTH and CS levels. In view of our previous studies on the effects of the adrenergic and 5-HT antagonists in the AMG and the present data, it is suggested that norepinephrine and 5-HT play an important role in the stimulatory effect of the AMG on the HPA axis. These effects depend on the presence of these excitatory neurotransmitters in the PVN.