ALPHA-1 AND ALPHA-2-ADRENERGIC RECEPTOR BLOCKADE INFLUENCES ANGIOTENSIN-II FACILITATION OF AVOIDANCE-BEHAVIOR AND STEREOTYPY IN RATS

Pretreatment of rats with prazosin (PRA), an alpha-1-adrenergic receptor blocker, abolished the increased rate of learning of conditioned avoidance responses stimulated by intracerebroventricular angiotensin II (AII) administration. Yohimbine (YOH), an alpha-2-receptor blocker, reversed the effect of AII. PRA did not affect, and YOH abolished, the improvement of recall of a passive avoidance behavior caused by AII. The stereotypies produced by apomorphine (APO) and amphetamine (AMP) were enhanced by AII. PRA changed neither stereotypy, but it abolished the AII effect in both cases. YOH did not alter APO stereotypy and abolished the enhancement of that behavior caused by AII. YOH increased AMP stereotypy and had an additive effect with AII. No significant changes of exploratory motor activity were caused by PRA, YOH, or their combination, with AII. These findings indicate that functioning alpha-1- and alpha-2-adrenergic receptors are necessary for the facilitation of learning by AII, while only alpha-2-receptors appear to be involved in AII improvement of recall. The central dopaminergic system may in part be responsible for the modulation by PRA and YOH of the effects of AII on learning and recall.