IMMUNOHISTOCHEMICAL DOUBLE-LABELING STUDY OF GONADOTROPIN-RELEASING-HORMONE (GNRH)-IMMUNOREACTIVE CELLS AND OXYTOCIN-IMMUNOREACTIVE CELLS IN THE PREOPTIC AREA OF THE DWARF GOURAMI, COLISA-LALIA

The distribution of gonadotropin-releasing hormone (GnRH)-immunoreacti ve (ir) cells in the preoptic area (POA) of the dwarf gourami, Colisa lalia, was immunohistochemically studied. These neurons form cell colu mns on both sides of the common ventricle, and their axons project to the pituitary gland by forming distinct bundles. Also examined was the distribution of isotocin (IST) cells in the POA by using an anti-oxyt ocin (OXT) serum which has been proven to crossreact with IST. These t wo kinds of immunoreactive cells were distributed quite similarly in t he POA. However, by using an immunofluorescence double-labeling method on thinner sections we found that a population of small IST cells in the ventral POA were also immunoreactive to GnRH, but that large IST c ells in the dorsal POA were not immunoreactive to GnRH, and small GnRH -ir cells in the most ventral POA were not immunoreactive to the OXT a ntiserum. In the pituitary gland, GnRH-ir fibers were found in both th e neurohypophysis and proximal pars distalis, but IST fibers were foun d only in the neurohypophysis.