title: 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.
authors.affiliation: Rudolf Magnus Institute, Medical Faculty, University of Utrecht, The Netherlands.
authors.forename: T A
authors.initials: TA
authors.lastname: Voorhuis
authors.forename: J P
authors.initials: JP
authors.lastname: Elands
authors.forename: E R
authors.initials: ER
authors.lastname: Kloet