Distribution of vasopressin and oxytocin binding sites in the brain and upper spinal cord of the common marmoset

The aim of this study was to label selectively and to map central vasopressin (AVP) and oxytocin (OT) binding sites in the common marmoset. [125I]VPA, a compound selective in rodents and human for the AVP V1a receptor, yielded the same labeling pattern as [3H]AVP, thus suggesting that most AVP receptors present in the marmoset brain are of the V1a subtype. Numerous areas exhibited AVP binding sites, among which the olfactory bulb, the accumbens nucleus, the bed nucleus of the stria terminalis, the hypothalamic suprachiasmatic, arcuate and ventromedial nuclei, the medial amygdaloid nucleus, the nucleus of the solitary tract and the cerebral cortex. Binding sites for [125I]OTA, a selective OT receptor antagonist in rat and human, were markedly less abundant than [125I]VPA ones, and, to a few exceptions, expressed in different areas. Neither AVP, nor OT binding sites were detected in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei identified by neurophysin immunoreactivity. Marked species-related differences were observed in the distribution of both AVP and OT binding sites. Altogether, our data provide a morphological basis to investigate the function of central AVP and OT in the marmoset.