Autoradiographic characterization of binding sites labelled with vasopressin in the brain of a urodele amphibian.

Because arginine vasotocin (AVT) activates male sexual behaviors in the rough-skinned newt (Taricha granulosa), quantitative autoradiography with radiolabelled arginine vasopressin (3H-AVP) was used to characterize putative AVT receptors in the telencephalon of this amphibian. Analyses were restricted to specific binding sites in the medial pallium, although dense binding also was observed in the dorsal pallium and amygdala pars lateralis. Binding of 3H-AVP to these sites was saturable, specific, reversible, of high affinity (Kd = 1 nM) and low capacity (57 fmol/mg protein). The rank order of potency of related peptides in inhibiting 3H-AVP binding was as follows: AVT greater than d(CH2)5[Tyr(Me)2]AVP (a mammalian pressor antagonist) greater than AVP, oxytocin, and [dPen1Tyr(Me)2]AVP (also a pressor antagonist) greater than mesotocin much greater than desGly(NH2)AVP, AVP fragment 4-9 and pressinoic acid. Thus, these binding sites appear to represent authentic central nervous system receptors for AVT. Furthermore, ligand specificity for the binding sites in this amphibian differ from that reported for AVP binding sites in rat brains. The AVT receptors in the medial pallium, dorsal pallium, and amygdala pars lateralis may represent site(s) of action where AVT elicits sexual behaviors in male T. granulosa.