Immunoreactive atrial natriuretic peptide and autoradiographic distribution of atrial natriuretic peptide binding sites in the brain of the Antarcticfish Chionodraco hamatus

The anatomical distribution of atrial natriuretic peptide (ANP)-immunoreact ive structures and the autoradiographic localization of ANP binding sites w ere studied in the brain of the Antarcric fish, Chionodraco hamatus. ANP-co ntaining elements were colocated with ANP binding sites in the dorsal media l and lateral subdivisions of the telencephalon, prethalamic nuclear comple x, and in the nucleus of the medial longitudinal fasciculus of the mesencep halon. However, mismatching was observed in other brain regions, particular ly at mesencephalic and metencephalic levels. In the pituitary, ANP immunor eactivity occurred only in the pars distalis, whereas ANP binding sites wer e localized in the whole pituitary. In this paper we describe the occurrenc e of ANP immunoreactivity and ANP binding sites in the brain and pituitary of an Antarctic fish. In particular, in the cerebellum and pituitary of C. hamatus, ANP binding sites are distributed in corresponding brain regions o f dipnoans, amphibians and mammals. The immunocytochemical and histoautorad iographic data suggest that ANP acts as neuromodulator in the brain of C. h amatus. Moreover, the presence of ANP-like substances in tanycytes lining t he diencephalic ventricle suggests a chemosensorial role for such liquor-co ntacting cells and a possible modulatory effect of ANP on the osmoregulatio n of the cerebrospinal fluid.