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) a nd augment oxytocin (OT) and prolactin (PRL) release in rats. We examined t he effects of intracerebroventricular (i.c.v.) injections of adrenoceptor a ntagonists on these neuroendocrine responses to conditioned fear or novel e nvironmental 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 bet a 2 antagonist, ICI118551, impaired the PRL but not the VP or OT response t o fear or novel environmental stimuli. In rats injected with a cll adrenoce ptor antagonist, benoxathian, conditioned fear stimuli did not significantl y induce the VP, OT or PRL responses. The effects of benoxathian were not d ue 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 condi tioned fear stimuli, as do beta 2 adrenoceptors in the prolactin response t o conditioned fear and novel environmental stimuli. We conclude that alpha 1 adrenoceptors play a facilitative role in VP, OT, PRL responses to condit ioned fear stimuli.