VASOTOCINERGIC INNERVATION OF SEXUALLY DIMORPHIC MEDIAL PREOPTIC NUCLEUS OF THE MALE JAPANESE-QUAIL - INFLUENCE OF TESTOSTERONE

The distribution of vasotocin (VT)-immunoreactive (IR) fibers was desc ribed in the preoptic and septal regions of the male quail brain. The density of VT-IR fibers was measured in the sexually dimorphic preopti c nucleus (POM) and lateral septum (SL) of adult male quail (Coturnix japonica) by means of quantitative image analysis. Experimental manipu lations of the hormonal environment in the peripubertal period influen ced this distribution. In both regions, the VT immunoreactivity was re duced or absent when males were castrated. The immunoreactivity was re stored to its original level in castrated males by Silastic implants o f testosterone. These changes were anatomically specific as evidenced by the fact that the density of VT fibers did not vary in the hypothal amo-neurohypohysial tract as a function of the endocrine condition of the subjects. No change was also observed in the number of VT-IR cells in the periventricular region close to the POM. Previously published data show that VT or its mammalian homolog, vasopressin are implicated in the control of a wide range of instinctive behaviors. The steroid- dependent VT afferents to the POM, a key area controlling male copulat ory behavior in quail could therefore be involved in the control of th e sexual behavior in this species. The outputs of the POM which contai ns steroid-receptors could therefore be modulated by steroids in two d ifferent ways: directly through the steroid receptors it contains and indirectly through its steroid-sensitive peptidergic afferents.