AN IODINATED VASOPRESSIN (V1) ANTAGONIST BLOCKS FLANK MARKING AND SELECTIVELY LABELS NEURAL BINDING-SITES IN GOLDEN-HAMSTERS

An arginine-vasopressin (AVP) derivative, [d(CH2)5,Sar7]AVP (SAVP), ha s been characterized as an antagonist to vasopressin V1 receptors. Usi ng AVP-dependent flank-marking behavior as a bioassay, it was possible to verify that iodinated SAVP (I-SAVP) retains biological activity wi thin the central nervous system, as the antagonist blocked the behavio r. Furthermore, I-125-SAVP was used to localize specific V1 binding si tes in the brain. The resulting binding was localized to discrete anat omical sites, and highly specific to V1-like receptors. While we confi rmed previous findings using H-3-AVP in golden hamsters, we also ident ified binding in many areas previously unreported (e.g., arcuate and p araventricular nuclei of the hypothalamus, tenia tecta, posteromedial cortical nucleus of the amygdala, and zona incerta), suggesting that I -125-SAVP provides a greater level of resolution. In addition, specifi c binding was observed in the lateral septum, anterior hypothalamus, a nd midbrain central gray, areas that have previously been shown to tri gger flank marking in response to AVP microinjection. The presence of AVP binding sites in limbic and mesencephalic areas involved in the re gulation of flank marking suggests that this neuropeptide may play an important role as a neurotransmitter at multiple levels in the neural circuits controlling this behavior.