Gonadotropin-releasing hormone (GnRH) neuronal systems in the pejerrey, Odontesthes bonariensis (Atheriniformes)

The brain of the pejerrey (Odontesthes bonariensis) has recently been shown to contain three forms of gonadotropin-releasing hormone (GnRH): salmon Gn RH (sGnRH. chicken GnRH-II (cGnRH-II) and pejerrey GnRH (pjGnRH), neverthel ess neuroanatomical studies on the distribution of these peptides are lacki ng. in this study we investigated the distribution of immunoreactive GnRH i n the brain of adult pejerrey. Four different policlonal antisera and a mon oclonal antibody against different GnRH variants were applied on cryosectio ns and visualized using the ABC method. Three antisera (PBL#49, sGnRH#2 and cII741) revealed three different immunoreactive areas: the terminal nerve ganglion (at the junction between the olfactory bulbs and the anterior tele ncephalon), the preoptic area just anterior to the hypothalamus and the mid brain tegmentum. Fibers immunoreactive to GnRH were detected in different b lain areas: the olfactory bulbs, the ventral thelencephalon. the hypothalam us. the mesencephalic area and an important innervation entering into the p ituitary gland. Two other antibodies (LRH13 and s1668) labeled the two nucl ei corresponding to the forebrain but not the midbrain tegmentum. As both a ntibodies have low crossreactivity to cGnRH-II, the data suggest that this group of cells express cGnRH-II. In summary, three different areas with imm unoreactivity to GnRH were detected in the pejerrey brain. The distribution of sGnRH, pjGnRH and cGnRH-II expressing neurons, is discussed.