Distribution of the vasotocin type 4 receptor throughout the brain of the chicken, Gallus gallus.

The vasopressin 1a receptor (V1aR) has been shown to have a wide distribution throughout the mammalian brain and pituitary gland and mediates a number of physiological functions as well as social behavior following the binding of its agonist, vasopressin. The avian receptor homologous to the V1aR is the vasotocin 4 receptor (VT4R). Its mRNA distribution has been documented in brain regions of two species of songbird; however, its complete protein distribution in the brain has not been published to date for any avian species. The present work utilizes an antibody made to a sequence of the chicken VT4R to map its distribution from the olfactory bulbs to the caudal end of the brainstem in Gallus gallus. Unexpectedly, immunoreactivity (ir) for the VT4R was found not only in neurons but also in glia located in 10 circumventricular organs (CVOs), olfactory bulbs, hippocampus, and septum. Use of a second antibody made against vimentin provided evidence that some dual-labeled glial cells were tanycytes and radial glia. Additionally, the VT4R was identified in nuclei related to motor function, including the oculomotor complex and motor nucleus of the fourth, fifth, sixth, seventh, tenth, and twelfth cranial nerves. Possible functions for the VT4R are suggested that should have relevance not only to avian species but to other vertebrates because most classes, except for mammals, use vasotocin as the natural ligand for that receptor.