Distribution of GnRH in the brain of the freshwater teleost Astyanax altiparanae.

GnRH is well known as a key decapeptide neurohormone involved in reproduction, stimulating the pituitary gland to release gonadotropins (LH and FSH), which, in turn, regulate steroidogenesis and gametogenesis. However, in addition to its reproductive functions, GnRH displays neuromodulatory roles with implications for sexual behavior. The pattern of distribution in the brain of GnRH may help reveal GnRH specific functions. Therefore, the main emphasis of this study is to detect the presence and distribution of GnRH in the brain of the freshwater teleost Astyanax altiparanae ("lambari"). The immunohistochemical method of peroxidase with an antibody raised against GnRH3 was used to detect the location of GnRHs in the brain and pituitary gland. Immunoreactivity to GnRH was found in the following encephalic areas: olfactory bulb, terminal nerve ganglion, preoptic area, nucleus of midbrain tegmentum, but also in torus longitudinalis, glomerular nucleus, and central and dorsal posterior nuclei of dorsal thalamus. In addition, cell bodies from neurons in the parvocellular and magnocellular periventricular nuclei and ventral tuberal nucleus along with many fibers including ones innervating the neurohypophysis were immunoreactive to a GnRH antiserum that detects all known eight GnRH peptides in teleosts. This is the first study describing the distribution of the complete GnRH system in the brain of A. altiparanae, which has great importance for aquaculture and ecology, and represents one of the major orders of South American teleosts--the Characiformes.