We recently isolated an oviposition-inducing peptide that was identified as avian galanin from the oviducts of the Japanese quail. Avian galanin was localized in neural fibers distributed in muscle layers in the uterine and vaginal oviduct regions, and potentiated spontaneous contractions of the uterus and vagina. To elucidate whether an oviposition-inducing effect of avian galanin is due to the direct action on the oviduct, therefore, a specific binding site for avian galanin was determined in the functional quail oviduct in this study. The binding of [ 125 I]iodoavian galanin was primarily located in the oviduct as well as the brain. The galanin binding was specifically inhibited as a function of the concentrations of both avian and rat galanins. The specific binding of avian galanin to the quail oviduct was temperature dependent and reached the maximum level for 1 h at 20°C. In several regions of the oviduct, a higher level of specific galanin binding was observed only in the uterus and vagina. In contrast, the specific binding was low in the isthmus and negligible in the magnum. A similar localization was evident in the functional chicken oviduct. The Scatchard plot analysis of the binding of avian galanin to the uterine preparation revealed that the dissociation constant (Kd) was 0.249 (95% confidence interval, 0.192-0.356) nM, and the number of binding sites was 1.13 (0.99-1.36) fmol per mg tissue, respectively. During development, the galanin-binding sites were apparent in the quail oviduct at 3 weeks of age and the number of binding sites markedly increased between 3 weeks and 3 months of age. However, there was no significant change in the Kd value in the developing quail oviduct. This is the first demonstration of the presence of galanin receptors in the reproductive tract, such as the uterine and vaginal oviduct. The present results suggest that the number of galanin receptors in the oviduct increases during development and that galanin acts directly on the mature uterus and vagina to induce their contractions. This mechanism may be essential to the avian oviposition.