Involvement of amygdalar alpha adrenoceptors in hypothalamo-pituitary-adrenocortical responses.

We have previously demonstrated that the facilitatory effect of the amygdala on the hypothalamo-pituitary-adrenocortical (HPA) axis responses to photic stimulation depends on the presence of norepinephrine (NE) in this region. In the present study we investigated the effect of alpha 1- and beta-adrenoceptor blockers, injected into the central amygdala nucleus, on the HPA responses. In intact freely moving rats, short photic stimulation caused depletion of CRH-41 from the median eminence, due to its release into the portal circulation and a rise in serum ACTH and corticosterone levels. This effect was markedly inhibited by injection of prazosin, an alpha 1-adrenoceptor blocker, but atenolol, a beta 1 blocker, had no effect. These data further indicate that amygdala NE plays a role in the activation of the HPA axis following neural stimuli and that this effect is mediated by alpha 1-adrenoceptors in the central amygdala.