AUTORADIOGRAPHIC LOCALIZATION OF OPIOID RECEPTORS IN VOCAL CONTROL REGIONS OF A MALE PASSERINE BIRD (JUNCO-HYEMALIS)

Previous studies have found opioid peptide-like immunoreactivity in av ian vocal control regions, but whether these regions contain receptors for opioid peptides has not been examined. To address this question, we used quantitative in vitro autoradiography to determine the anatomi cal distribution and to measure the densities of mu, delta, and kappa opioid receptors in vocal control regions (area X, higher vocal center , and nucleus intercollicularis) of adult male dark-eyed juncos (Junco hyemalis). To evaluate whether opioid receptor densities in these reg ions depend on the activity of the reproductive system, we also measur ed these densities in birds collected during the spring, summer, and f all. We found area X, the higher vocal center, and nucleus intercollic ularis to contain the three receptor types under study, but opioid rec eptor densities did not vary seasonally in any of these regions. The p resence of specific opioid receptors in avian vocal control regions su ggests the participation of opioids in the control of vocal behavior. This participation may consist of short-term (e.g., auditory processin g) and/or long-term (e.g., neuronal plasticity) influences. (C) 1995 W iley-Liss, Inc.