Colocalization of GnRH binding sites with gonadotropin-, somatotropin-, somatolactin-, and prolactin-expressing pituitary cells of the pejerrey, Odontesthes bonariensis, in vitro

Previous studies in the pejerrey, Odontesthes bonariensis, have demonstrate d that fibers with immunoreactivity to gonadotropin-releasing hormone (ir-G nRH) reach all areas of the pituitary gland, the rostral pars distalis (RPD ), the proximal pars distalis (PPD), and the pars intemedia (PI). A close a ssociation was shown between ir-GnRH fibers and gonadotropin (GtH)-, growth hormone (GH)-, somatolactin (SL)-, and prolactin (PRL)-expressing cells. T he presence of only one GnRH variant, suspected to be a novel form, has bee n shown in pituitary extracts of this fish. In addition, GnRH may stimulate GtHs, GH, SL, and PRL levels in different fish species. The objective of t he present study was to seek GnRH receptors and therefore colocalization wi th GtHs, GH, SL, and PRL cells in O. bonariensis using a pituitary primary cell culture system. GnRH binding sites were revealed by autoradiography of an iodinated superactive GnRH agonist ([I-125]GnRH-A) and pituitary cells were identified by immunocytochemistry using piscine antisera. Following au toradiography, silver grains representing specific [I-125]GnRH-A binding we re associated with anti GtH, GH, SL, and PRL positive cells. These results demonstrate the presence of GnRH binding sites on these cells. It is sugges ted that GnRH may play a wide role in the neuroendocrine control of differe nt pituitary hormones in addition to the GtHs. (C) 1999 Academic Press.