PASSIVE-AVOIDANCE LEARNING INVOLVES ALPHA-2-NORADRENERGIC RECEPTORS IN A DAY-OLD CHICK

DAY-OLD chicks were trained on one-trial passive avoidance task, using methyl-anthranilate (MeA) as an aversive substance. Bilateral pharmac ological manipulation of the intermediate hyperstriatum ventrale was p erformed by intracerebral application of an alpha 2-noradrenergic agon ist, clonidine (5 mu M), or an antagonist, rauwolscine (300 mu M). Onl y rauwolscine application (pre- or post-training) induced significant memory impairment. Quantitative receptor autoradiography was used to d etermine the kinetic properties of the binding sites for [H-3]clonidin e or [H-3]rauwolscine in MeA-trained or water-trained (control) chicks , in forebrain areas known to be involved in avoidance learning. Scatc hard analysis revealed that MeA-training resulted in a significant bil ateral upregulation in the number of [H-3]rauwolscine binding sites (B -max) in the area elf hyperstriatum ventrale. These findings suggest t he importance of activation of alpha 2-noradrenergic receptors in aver sive learning in chicks. (C) 1998 Rapid Science Ltd.