Natriuretic peptide binding sites in the brain of the Atlantic hagfish, Myxine glutinosa

We have previously used immunohistochemistry to show that the brain of the hagfish, Myxine glutinosa, contains a rich distribution of natriuretic pept ide-immunoreactive elements with the densest distribution occurring in the telencephalon and the diencephalon. In this study, the distribution of I-12 5-rat ANP and I-125-porcine CMP binding sites was determined in the brain o f M. glutinosa. The binding pattern of I-125-rat ANP and I-125-porcine CNP showed similarities; however, some differences were observed in the olfacto ry bulb and the caudal brain regions. Specific I-125-rat ANP and I-125-porc ine CNP binding was observed in the olfactory bulb, outer layers of the pal lium, and in regions of the diencephalon. Very little specific binding was observed in the habenula and the primordium hippocampi. In the diencephalon , a distinct zone of specific I-125-rANP binding separated a region of mode rate binding in the lateral regions of the diencephalon from the thalamic a nd hypothalamic nuclei. Moderate levels of specific I-125-rANP binding were observed in the mesencephalon and medulla oblongata; little or no I-125-po rcine CNP binding was observed in these regions. The data, in combination w ith previous immunohistochemical studies, show that the natriuretic peptide system of the hagfish brain is well-developed and suggest that natriuretic peptides have a long evolutionary history as neurotransmitters and/or neur omodulators in the vertebrate brain. J. Exp. Zool. 284:407-413, 1999. (C) 1 999 Wiley-Liss, Inc.