MELANIN-CONCENTRATING HORMONE SYSTEM IN THE BRAIN OF THE LUNGFISH PROTOPTERUS ANNECTENS

The neurochemical anatomy of the lungfish brain is of particular inter est, because many features in these animals might be representative of the common ancestor of land vertebrates. In the present study, me hav e investigated the localization and biochemical characteristics of mel anin-concentrating hormone (MCH)-immunoreactive material in the centra l nervous system of the African lungfish, Protopterus annectens. The m ost prominent group of MCH-immunoreactive cell bodies was found in the dorsal hypothalamus. Additional groups of MCH-immunoreactive perikary a were detected in the telencephalon within the medial and dorsal pall ium, the medial subpallium, and the ventral part of the lateral subpal lium. Brightly immunofluorescent nerve fibers were seen in the anterio r olfactory nucleus, the ventral part of the medial pallium, the media l subpallium, and the anterior preoptic area. In the diencephalon, the hypothalamus and the medial region of the dorsal thalamus exhibited a dense accumulation of fibers., MCH-immunoreactive fibers were also fo und in the tectum and the tegmentum of the mesencephalon and within th e reticular formation of the rhombencephalon. In the pituitary, severa l small groups of cells of the intermediate lobe showed a bright fluor escence. Reversed-phase high-performance liquid chromatography (HPLC) analysis of diencephalon and pituitary extracts resolved a major MCH-i mmunoreactive peak that coeluted with synthetic salmon MCH. The distri bution of MCH in the brain of P. annectens suggests that, in lungfishe s, this peptide may exert neuromodulator or neurotransmitter functions . The presence of MCH-like immunoreactivity in the intermediate lobe o f the pituitary indicates that, in dipnoans, MCH may also act as a typ ical pituitary hormone. (C) 1998 Wiley-Liss, Inc.