Autoradiographic localization of opioid receptors in vocal control regions of a male passerine bird (Junco hyemalis)

Abstract

Previous studies have found opioid peptide-like immunoreactivity in avian 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 anatomical 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 regions depend on the activity of the reproductive system, we also measured these densities in birds collected during the spring, summer, and fall. We found area X, the higher vocal center, and nucleus intercollicularis to contain the three receptor types under study, but opioid receptor densities did not vary seasonally in any of these regions. The presence of specific opioid receptors in avian vocal control regions suggests the participation of opioids in the control of vocal behavior. This participation may consist of short-term (e.g., auditory processing) and/or long-term (e.g., neuronal plasticity) influences.

Expression of μ- and δ-opioid receptors in song control regions of adult male zebra finches (Taenopygia guttata)

“…A qRT-PCR analysis demonstrated that there were no significant differences in m-OR mRNA expression between HVC and PNP, and the expression of d-OR mRNA was uniformly lower than m-OR mRNA expression in these regions. Our findings were similar to those of Gulledge and Deviche (1995) who demonstrated that the expression of m-ORs was greater than that of d-ORs in HVC in juncos. Whereas HVC of adult male juncos expressed low levels of d-ORs and this nucleus appeared as a clear area within the surrounding PNP, the expression of m-ORs was uniform throughout PNP, inclusive of HVC (Gulledge and Deviche, 1999).…”

“…That is, Area X expresses higher levels of m-OR mRNA compared to MSt in adult and juvenile juncos of both sexes, but not in adult male zebra finches, the reasons for which are unclear. Although Gulledge and Deviche (1995) had suggested that these differences in OR expression were unlikely to be linked to singing since the densities of m-ORs in Area X did not vary seasonally in male juncos, recent evidence suggests otherwise. Wada et al (2006) have shown that proenkephalin (the peptide precursor of enkephalin) is upregulated in the processes of Area X (and HVC) neurons during singing in adult male zebra finches.…”

“…Although it is difficult to assign reasons for the differences in OR expression in zebra finches and juncos, it is possible that the relative contributions of d-ORs in modulating vocalizations may differ in the two species of songbirds. As in the case of Area X, Gulledge and Deviche (1995) have shown that OR densities did not vary in HVC in singing (breeding) or non-singing adult males or with age, suggesting that these receptors were not linked to seasonal changes in singing or to song learning, respectively. However, Wada et al (2006) have shown that the proenkephalin mRNA expression was higher in HVC of juvenile male zebra finches compared to adult males during singing.…”

Opioid receptor densities analyzed across seasons in the POM and VTA of the dark-eyed junco, Junco hyemalis

“…Males continue to sing during the summer breeding season but rarely thereafter, when they prepare to migrate south. A previous study identified opioid receptors in brain regions of the junco song system including the HVC, RA, and Area X, which control song learning and production, and found no seasonal differences in receptor densities (Gulledge and Deviche, 1995). Given the involvement of VTA and POM opioid receptors in motivation or reward, we hypothesized that birds express opioid receptors in these regions and receptors would be present at higher densities during than outside the breeding season.…”

Recent advances in behavioral neuroendocrinology: Insights from studies on birds

“…Administration of T, or its metabolite E 2 , increases neuronal number and size in HVC and Area X in song sparrows, white-crowned sparrows (Zonotrichia leucophrys gambelii), and darkeyed juncos (Junco hyemalis), and increases neuron size in RA (Gulledge & Deviche, 1995;Tramontin et al, 2003;Soma et al, 2004). The arborization of neurons within RA is profoundly affected by E 2 in the adult canary, with the number of dendrites and synaptic profiles increasing with steroid administration (DeVoogd & Nottebohm, 1981).…”