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

Abstract

The brain of the pejerrey (Odontesthes bonariensis) has recently been shown to contain three forms of gonadotropin-releasing hormone (GnRH): salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and pejerrey GnRH (pjGnRH), nevertheless neuroanatomical studies on the distribution of these peptides are lacking. In this study we investigated the distribution of immunoreactive GnRH in the brain of adult pejerrey. Four different policlonal antisera and a monoclonal antibody against different GnRH variants were applied on cryosections 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 telencephalon), the preoptic area just anterior to the hypothalamus and the midbrain tegmentum. Fibers immunoreactive to GnRH were detected in different brain areas: the olfactory bulbs, the ventral thelencephalon, the hypothalamus, the mesencephalic area and an important innervation entering into the pituitary gland. Two other antibodies (LRH13 and s1668) labeled the two nuclei corresponding to the forebrain but not the midbrain tegmentum. As both antibodies have low crossreactivity to cGnRH-II, the data suggest that this group of cells express cGnRH-II. In summary, three different areas with immunoreactivity to GnRH were detected in the pejerrey brain. The distribution of sGnRH, pjGnRH and cGnRH-II expressing neurons, is discussed. Abbreviations: C‐ cerebelum ;C M ‐corpus mamilaris ;D cd ‐area dorsalis telencephali pars centralis ;D d ‐ area dorsalis telencephali pars dorsalis ;D l ‐area dorsalis telencephali pars lateralis ;D lv ‐area dorsalis telencephali pars lateralis ;D m ‐area dorsalis telencephali pars medialis ;M t ‐midbrain tegmentum; NDLl ‐ nucleus difusus lobi inferioris ;N G ‐nucleus glomerulosus ;N PGC ‐nucleus preglomerulosus pars medialis ;N PP ‐ nucleus preopticus periventricularis ;N R ‐nucleus rotundus ;N T ‐nucleus tenia; Ob ‐ olfactory bulbs; Oc ‐ optic chiasma; ON ‐ optic nerve; Otec ‐ optic tectum; Pit ‐ pituitary; Tel ‐ telencephalon; Tl ‐ torus longitudianalis; TNG ‐ terminal nerve ganglion; Vd ‐ area ventralis telencephali pars centreli ; area ventralis telencephali pars ventralis.