IMMUNOHISTOCHEMICAL DEMONSTRATION OF OXYTOCIN-LIKE, NEUROPEPTIDE Y-LIKE AND GONADOTROPIN-RELEASING HORMONE-LIKE SUBSTANCES IN THE HYPOTHALAMOHYPOPHYSEAL SYSTEM OF AYU, PLECOGLOSSUS-ALTIVELIS ALTIVELIS, IN OSMOTICALLY DIFFERENT ENVIRONMENTS
Y. Honma et al., IMMUNOHISTOCHEMICAL DEMONSTRATION OF OXYTOCIN-LIKE, NEUROPEPTIDE Y-LIKE AND GONADOTROPIN-RELEASING HORMONE-LIKE SUBSTANCES IN THE HYPOTHALAMOHYPOPHYSEAL SYSTEM OF AYU, PLECOGLOSSUS-ALTIVELIS ALTIVELIS, IN OSMOTICALLY DIFFERENT ENVIRONMENTS, Ichthyological research, 45(1), 1998, pp. 35-42
To ascertain the role of neuropeptides on the hypothalamo-hypophysial
system of a fish in osmotically different environments, an immunohisto
chemical study of oxytocin (OXT), neuropeptide Y (NPY) and gonadotropi
n-releasing hormone (GnRH) was carried out on the anadromous salmonoid
fish, Plecoglossus altivelis altivelis, commonly known as Ayu. River
fish caught were acclimatized in a freshwater aquarium, half of them b
eing subsequently kept as a control group and the remainder being tran
sferred to a sea water aquarium, through 1/3 diluted sea water, as an
experimental group. OXT-like immunoreactivity as demonstrated in the n
eurosecretory pathway, having the same pattern was that shown by aldeh
yde fuchsin staining. Noticeably, a mass of nucleus preopticus (NPO) a
nd a marginal portion of the pars nervosa in the control group became
strongly immunoreactive, whereas a very weak reaction was obtained in
the sea water-retained fish, suggesting the release of the labelled su
bstance. In the latter, NPY-like substance was widely distributed in t
he brain without NPO, with the positive substance being dense in the t
erminal rami of the pars nervosa bordering the pars distalis. However,
no remarkable difference in GnRH-like and NPY-like immunoreactivities
in the hypothalamo-hypophysial system was apparent between the two gr
oups. These results suggested that OXT (probably isotocin)-like substa
nce may play a role in osmoregulation.