Vasotocin Target Sites in the Capsular Region Surrounding the Nucleus Robustus Archistriatalis of the Canary Brain

Abstract

Abstract The aim of this study was to characterize neurohypophyseal hormone receptors in the brain of the canary (Serinus canarius) by using autoradiographical and biochemical procedures with a radioiodinated vasotocin analogue, [(125) l]d(CH(2))(5)[Tyr(Me)(2), Thr(4), Orn(8), Tyr-NH(2) (9)]vasotocin ([(125) I]-OTA). This synthetic analogue was used previously to identify a population of oxytocin-like receptors in the rat brain that have high affinity for vasotocin. In vitro autoradiography revealed high affinity binding sites for [(125) I]-OTA in the canary brain in the archistriatum surrounding the nucleus robustus archistriatalis. Scatchard analysis of [(125) I]-OTA binding to a synaptic membrane fraction prepared from the archistriatal region including the nucleus robustus archistriatalis indicated the presence of a single population of binding sites (K(d)= 0.05 nM; B(max)= 4 fmol/mg protein). Displacement studies revealed that the order of potency of certain peptides to inhibit [(125) I]-OTA binding was as follows: vasotocin (K(i)= 0.4 nM) > oxytocin = vasopressin > mesotocin (K(i)= 8.0 nM). The administration of testosterone to female canaries did not affect [(125) I]-OTA labelling in the archistriatum detected by autoradiography and did not influence [(125) I]-OTA binding constants in the membrane binding assay. In conclusion, this study provides morphological and biochemical evidence of a vasotocin-target site in the archistriatum in close association with the central vocal control circuit in the canary brain.