K. Tsutsui et al., DEMONSTRATION, LOCALIZATION, AND DEVELOPMENT OF GALANIN RECEPTORS IN THE QUAIL OVIDUCT, The Journal of experimental zoology, 277(1), 1997, pp. 57-65
We recently isolated an oviposition-inducing peptide that was identifi
ed as avian galanin from the oviducts of the Japanese quail. Avian gal
anin was localized in neural fibers distributed in muscle layers in th
e uterine and vaginal oviduct regions, and potentiated spontaneous con
tractions of the uterus and vagina. To elucidate whether an ovipositio
n-inducing effect of avian galanin is due to the direct action on the
oviduct, therefore, a specific binding site for avian galanin was dete
rmined in the functional quail oviduct in this study. The binding of [
I-125]iodo-avian galanin was primarily located in the oviduct as well
as the brain. The galanin binding was specifically inhibited as a func
tion of the concentrations of both avian and rat galanins. The specifi
c binding of avian galanin to the quail oviduct was temperature depend
ent and reached the maximum level for 1 h at 20 degrees 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 bin
ding was low in the isthmus and negligible in the magnum. A similar lo
calization was evident in the functional chicken oviduct. The Scatchar
d plot analysis of the binding of avian galanin to the uterine prepara
tion revealed that the dissociation constant (Kd) was 0.249 (95% confi
dence 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 week
s 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 demon
stration of the presence of galanin receptors in the reproductive trac
t, such as the uterine and vaginal oviduct. The present results sugges
t that the number of galanin receptors in the oviduct increases during
development and that galanin acts directly on the mature uterus and v
agina to induce their contractions. This mechanism may be essential to
the avian oviposition. (C) 1997 Wiley-Liss, Inc.