The distribution and plasticity of [3H]vasopressin-labelled specific binding sites in the canary brain

[3H]Vasopressin was used to detect and to quantitate specific binding sites with in vitro receptor autoradiography in the canary brain. A discrete regional distribution of [3H]vasopressin-labelled binding sites was observed. A high density of specific binding sites was present in the medial posterior hypothalamic nucleus, the superficial layer of the optic tectum, the area ventralis of Tsai (AVT), the nucleus pretectalis, the habenula, the nucleus of Darkschewitch and the nucleus interstitialis. A low density occurred in the nucleus robustus archistriatalis of female birds. However, after testosterone treatment the density of the sites in this area as well as in the AVT increased 2-fold. [3H]Vasopressin binding was displaced to the same extent by excess vasopressin as well as by vasotocin. Moreover, the [3H]vasopressin-labelled brain regions are innervated by immunoreactive vasotocin fibers and terminals. It seems likely therefore that the labelled sites represent putative vasotocin receptors.