Role of adrenoceptors in vasopressin, oxytocin and prolactin responses to conditioned fear stimuli in the rat

Conditioned fear or novel environmental stimuli suppress vasopressin (VP) and augment oxytocin (OT) and prolactin (PRL) release in rats. We examined the effects of intracerebroventricular (i.c.v.) injections of adrenoceptor antagonists on these neuroendocrine responses to conditioned fear or novel environmental stimuli in male rats. A beta 1 antagonist, metoprolol, blocked the VP but not the OT or PRL response to conditioned fear stimuli, but did not abolish neuroendocrine responses to novel environmental stimuli. A beta 2 antagonist, ICI118551, impaired the PRL but not the VP or OT response to fear or novel environmental stimuli. In rats injected with a cll adrenoceptor antagonist, benoxathian, conditioned fear stimuli did not significantly induce the VP, OT or PRL responses. The effects of benoxathian were not due to a general reduction of arousal, since benoxathian did not prevent the VP, OT or PRL response to novel environmental stimuli. These data suggest that beta 1 adrenoceptors play a selective role in the VP response to conditioned fear stimuli, as do beta 2 adrenoceptors in the prolactin response to conditioned fear and novel environmental stimuli. We conclude that alpha 1 adrenoceptors play a facilitative role in VP, OT, PRL responses to conditioned fear stimuli.