IMMUNOREACTIVE PHE-MET-ARG-PHE-NH2-LIKE PEPTIDES IN THE BRAIN OF THE ANTARCTIC ICEFISH, CHIONODRACO-HAMATUS

The distribution of Phe-Met-Arg-Phe-NH2 (FMRFamide)-like immunoreactiv e peptides was investigated in the brain of the antarctic icefish, Chi onodraco hamatus, using the indirect immunofluorescence technique. Thr ee main groups of immunoreactive perikarya were respectively localized in the nucleus entopeduncularis of the telencephalon, the nucleus pre opticus periventricularis of the hypothalamus, and within the nucleus oculomotorius of the mesencephalon. Delicate FMRFamide positive nerve fibers were distributed in several brain regions of the forebrain and brainstem. In particular, these fibers densely innervated the caudal p art of the dorsomedial pallium, the hypothalamus, the thalamus, the me sencephalic tegmentum and the optic tectum. The distribution pattern o f the FMRFamide-like immunoreactivity was compared with that reported in previous studies in other teleost species. The anatomical organizat ion of the FMRFamide-like immunoreactive peptidergic system in the bra in of Chionodraco hamatus suggests that a FMRFamide-like peptide may p lay a role as a neuromodulator in fish adapted to the extreme Antarcti c environment.