Corticotropin releasing factor in the brain of the gymnotiform fish, Apteronotus leptorhynchus: Immunohistochemical studies combined with neuronal tract tracing

The expression of corticotropin-releasing factor (CRF) has been studied by immunohistochemistry in the brain of the gymnotiform fish, Apteronotus lept orhynchus. Labeled somata were found exclusively in the posterior subdivisi on of the nucleus preopticus periventricularis and in the hypothalamus ante rioris, where these cells form a continuous cluster of neurons. Combination of anti-peptide immunohistochemistry with an in vitro tract-tracing techni que confirmed that at least some of these neurons project to the pituitary. Additional terminal fields were present in the following areas of the tele ncephalon and the diencephalon: ventral subdivision of the ventral telencep halon, supracommissural subdivision of the ventral telencephalon, anterior subdivision of the nucleus preopticus periventricularis, inferior subdivisi on of the nucleus recessus lateralis, central posterior/ prepacemaker nucle us, hypothalamus dorsalis and lateralis, medial subdivision 2 of the nucleu s recessus lateralis, and in the region between the dorsal edge of the nucl eus tuberis anterior on the one side and both the glomerular nucleus and th e central nucleus of the inferior lobe on the other side. It is likely that the projection of CRF-expressing neurons of the posterior subdivision of t he nucleus preopticus periventricularis/hypothalamus anterioris to the pitu itary provides, similarly as in other fishes, the neural substrate for the activation of the hypothalamo-pituitary adrenal axis through CRE In additio n to this function, CRF may be involved in the regulation of several other processes, including neural control of communicatory behavior exerted by ne urons of the central posterior/prepacemaker nucleus. (C) 1999 Academic Pres s.