Distribution of vasopressin and oxytocin receptors in the rat spinal cord: sex-related differences and effect of castration in pudendal motor nuclei.

The distribution of vasopressin and oxytocin receptors was established by in vitro autoradiography in the spinal cord of adult rats of either sex, as well as in male castrates. In both males and females, high concentrations of vasopressin binding sites were found in a few groups of somatic motoneurons: the large lateral group at the cervicothoracic junction in segments C8 and Th1; the small medial group in segments L3-L5; and the pudendal and retrodorsolateral nuclei in segments L5-L6. The extension and intensity of labelling in pudendal nuclei were markedly lower in females than in males, in particular in the dorsomedial nucleus, where binding was either not or hardly detectable. Gonadectomy in males resulted in a significant reduction of binding in pudendal nuclei, but not in other labelled motor nuclei. Moderate amounts of vasopressin binding sites were also found evenly distributed throughout the central gray at all segmental levels. Oxytocin binding sites were detectable in all spinal segments, but in low amounts and restricted to the superficial layers of the dorsal horn. The abundance of vasopressin binding sites in the central gray suggests that vasopressin may be involved in most spinal functions. The permanent expression of vasopressin binding sites in pudendal motor nuclei of is particular interest with regard to the known plasticity of pudendal motoneurons.