Central vasotocin-immunoreactive system in a male passerine bird (Junco hyemalis).

Previous investigations have identified regions of the avian brain that contain immunoreactive vasotocinergic (VT-ir) cell bodies and fibers. These studies exclusively used domesticated species, and the relevance of the findings for free-living birds has not been established. The present study used immunocytochemistry to determine the neuroanatomical distribution of the VT-ir system in the brain of a well-studied male passerine bird (dark-eyed junco, Junco hyemalis) obtained from a natural population in interior Alaska (65 degrees N, 147 degrees W). VT-ir cell bodies were observed in several brain regions (paraventricular and supraoptic nuclei, nucleus of the stria terminalis), where they have been described in other oscine species. VT-ir fibers were widespread in many brain regions and were especially abundant in the medial preoptic nucleus, the basal region of the septum, and the hypothalamic-neurohypophyseal tract. Fibers were also present in brain regions that are involved in the control of vocal behavior including the ventromedial capsular region of the nucleus robustus archistriatalis and the dorsomedial portion of the mesencephalic nucleus intercollicularis. The widespread brain distribution of VT-ir cell bodies and fibers in juncos generally resembles that of domestic birds and suggests a role for this neuropeptide in the control of reproductive behavior and physiology.