Immunocytochemical localization and ontogenic development of ?-melanocyte-stimulating hormone (?-MSH) in the brain of a pleuronectiform fish, barfin flounder

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Abstract
α-Melanocyte-stimulating hormone (α-MSH) is a pituitary hormone derived by post-translational processing from proopiomelanocortin and is involved in background adaptation in teleost fish. It has also been reported to suppress food intake in mammals. Here, we examined the immunocytochemical localization of α-MSH in the brain and pituitary of a pleuronectiform fish, the barfin flounder (Verasper moseri), as a first step in unraveling the possible function of α-MSH in the brain. The ontogenic development of the α-MSH system was also studied. In the pituitary, α-MSH-immunoreactive (ir) cells were preferentially detected in the pars intermedia. In the brain, α-MSH-ir neuronal somata were located in the nucleus tuberis lateralis of the basal hypothalamus, and α-MSH-ir fibers were located mainly in the telencephalon, hypothalamus, and midbrain. α-MSH-ir neuronal somata did not project their axons to the pituitary. The α-MSH-ir neurons differed from those immunoreactive to melanin-concentrating hormone. α-MSH cells in the pituitary and α-MSH-ir neuronal somata in the brain were first detected 1 day and 5 days after hatching, respectively. The distribution of α-MSH-ir cells, neuronal somata, and fibers showed a pattern similar to that in adult fish 30 days after hatching. These results indicate that the functions of α-MSH in the brain and pituitary are different and that α-MSH plays physiological roles in the early development of the barfin flounder.

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