HYPOTHALAMIC AND EXTRAHYPOTHALAMIC SAUVAGINE-LIKE IMMUNOREACTIVITY INTHE BULLFROG (RANA-CATESBEIANA) CENTRAL-NERVOUS-SYSTEM

In the present study, immunocytochemistry and radioimmunoassay were us ed to investigate the presence of sauvagine in both hypothalamic and e xtrahypothalamic areas of the central nervous system (CNS) of the bull frog (Rana catesbeiana) using a specific antiserum raised against synt hetic non-conjugated sauvagine (SVG), a frog (Phyllomedusa sauvagei) s kin peptide of the corticotropin-releasing factor (CRF) family. Sauvag ine-immunoreactive (SVG-ir) bipolar neurons were found in the nucleus of the fasciculus longitudinalis medialis located in the rostral mesen cephalic tegmentum. In the tectal mesencephalon, beaded SVG-ir fibres were present in the optic tectum, and in the torus semicircularis. Abu ndant SVG-ir varicose fibres were seen in the granulosa layer of the c erebellum, the nucleus isthmi, and the obex of the spinal cord. SVG-ir fibres were also seen by the alar plate of the rombencephalon. In the diencephalon, the antiserum stained parvocellular neurons of the preo ptic nucleus (PON) which extended their dendrites into the cerebro-spi nal fluid (CSF) of the third ventricle and projected their ependymofug al fibres to the zona externa (ZE) of the median eminence. Immunoposit ive fibres were also present in the medial forebrain bundle at the chi asmatic field, the posterior thalamus, the pretectal gray, and the ven trocaudal hypothalamus. In the telencephalon (forebrain), SVG-ir fibre s were seen in the medial septum, the lateral septum, and the amygdala . The SVG immunoreactivity could not be detected after using the SVG a ntiserum previously immunoabsorbed with synthetic SVG (0.1 mu M), but immunoblock of the antiserum with sucker (Catostomus commersoni) urote nsin I (sUI), sole (Hippoglossoides elassodon) urotensin I, sucker CRF , rat/human CRF, or ovine CRF (0.1-10 mu M) did not eliminate visualiz ation of the immunoreactivity. In radioimmunoassay, the SVG antiserum did not crossreact with sUI, or the SVG fragments SVG(1-16), SVG(16-27 ), and SVG(26-34), but it recognized the C-terminal fragment SVG(35-40 ). Crossreaction with mammalian ovine CRF and rat/human CRF was neglig ible. Both hypothalamic and mesencephalic extracts gave parallel displ acement curves to SVG. The results suggest the presence in the bullfro g brain of a SVG-like neuropeptide, i.e., a peptide of the CRF family, that either is SVG or shares high homology with the C-terminus of tha t peptide. The function of this neuropeptide in amphibians is not know n at this time, but based on its anatomical distribution to the ZE it could affect the release of adrenocorticotropin (ACTH) or other substa nces from the amphibian pars distalis. Involvement of the SVG-like pep tide in behavioural (forebrain), visual (thalamus-tegmentum mesencepha li-pretectal gray-optic tectum), motor coordination (cerebellum), and autonomic (spinal) functions, as well as an undefined interaction with the CSF in the bullfrog, seems likely. (C) 1996 Wiley-Liss, Inc.