Autoradiographic Detection of Oxytocin- and Vasopressin-Binding Sites in Various Subnuclei of the Bed Nucleus of the Stria Terminalis in the Rat. Effects of Functional and Experimental Sexual Steroid Variations

Oxytocin- and vasopressin-binding sites were detected by autoradiography on films and on emulsion-coated sections of rat brains using highly selective [¹²⁵|]-labelled oxytocin and vasopressin antagonists. Two distinct areas with high concentrations of oxytocin-binding sites were detected in the bed nucleus of the stria terminalis: 1) the principal encapsulated nucleus and the associated cell-sparse zone in the posterior medial part, and 2) the oval nucleus in the anterior lateral part. A weak diffuse labelling was, in addition, detected around the oval nucleus in the anterior lateral and anterior dorsal areas. The vasopressin-binding sites were restricted to the anterior lateral part of the bed nucleus of the stria terminalis where they were highly concentrated in the juxtacapsular nucleus and present with lower density in a discrete cell group dorsal to the oval nucleus. Autoradiographic analyses of the bed nucleus of the stria terminalis from pregnant, lactating and ovariectomized rats (oestradiol treated or not) indicated that only the oxytocin-binding sites in the principal encapsulated nucleus and the associated cell-sparse zone were oestrogen-dependent. These observations are in agreement with earlier data suggesting that the two major divisions of the bed nucleus of the stria terminalis are involved in distinct regulations. The anterior lateral part, including the oval nucleus in which oxytocin receptors are not oestrogen-dependent, is, rather, involved in central autonomie regulations. The posterior medial part, where oestrogen-dependent oxytocin receptors are concentrated in the principal encapsulated nucleus and the associated cell-sparse zone, is implicated in neuroendocrine regulations and in reproductive behaviour.