INHIBITORY ROLE OF OPIOID-PEPTIDES IN THE REGULATION OF AGGRESSIVE AND SEXUAL BEHAVIORS IN MALE JAPANESE-QUAILS

We have recently isolated three opioid peptides, i.e., Met- and Leu-en kephalins and Met-enkephalin-Arg(6)-Phe(7), from the avian brain. Furt hermore, electrophysiological studies have shown that the dominant eff ect of these enkephalins on preoptic and hypothalamic neurons is an in hibition of neuronal activities in the male Japanese quail. The hypoth alamus and preoptic area are known to be involved in the control of ma le reproductive behaviors, such as aggressive and sexual behaviors. To determine the functional role of opioid peptides in these reproductiv e behaviors, therefore, the present study was undertaken using adult m ales of the Japanese quail. We examined behavioral changes following a n injection of naloxone (0.2, 2.0, and 20.0 nmol), a nonselective opio id receptor antagonist, or D-Ala(2)-Met(5)-enkephalinamide (DALA; 0.2, 2.0, and 20.0 nmol), a selective delta opioid receptor agonist, into the preoptic and anterior hypothalamic regions. Naloxone treatment sho wed a significant increase in the frequency of several aggressive acti ons and the effect was dose dependent. In contrast, DALA treatment sig nificantly decreased the frequency of aggressive actions in a dose-dep endent manner. Similar significant effects of these two drugs were obs erved in the sexual behavior. These findings provide the first evidenc e for the role of opioid peptides in the reproductive behaviors in the bird and suggest an inhibitory action of opioid to evoke the behavior s. (C) 1997 Wiley-Liss, Inc.