Testosterone Modulation of Peptidergic Pathways in the Septo-Preoptic Region of Male Japanese Quail

Multiple peptidergic innervation occurs in prosencephalic regions of quail that are characterized by a wide distribution of sex steroid receptors or gonadotropin releasing hormone elements, suggesting that neuropeptides could influence circuitries involved in the control of reproductive activities in birds. In the present study we investigated the existence of a testosterone (T) dependent modulation of peptidergic patways in the septo-preoptic region of quail. We quantitatively analyzed the immunocytochemical distribution of vasotocin (VT), substance P, neuropeptide Y (NPY), and vasoactive intestinal polypeptide (VIP) in intact, castrated, or castrated T-treated male quail. In intact males the distribution of the investigated peptidergic structures was peptide-specific and region-specific. NPYor VT-immunoreactive (ir) structures were detected in both the medial preoptic nucleus (POM) and the septum, whereas VIP-ir elements were particularly abundant in the latter region and almost absent in the POM. The reduction of T circulating levels after castration markedly decreases the VT innervation of the POM and of the lateral septum. The innervation was completely restored by T treatement. On the contrary, castration resulted in an increase of the VIP innervation of the septum at its most caudal level. Hence, T exerted an opposite effect upon these two neuropeptide systems inducing a decrease of VIP-ir fibres and an enhancement of VT-ir elements. Our results confirm previous data on T-dependent VT innervation of the septal area of the canary and of several mammalian species. Additionally, in quail the VT-ergic innervation of preoptic region is modulated by T. Further studies should clarify wheather the T-sensitive VT innervation of the POM comes from intrinsic or extrinsic