Brain hormones and appetite in fish

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1. Melanin-concentrating hormone (MCH) of the barfin flounder is composed of 17 residues, which differs from salmon MCH at a position 2. The biological activity of synthetic MCH was demonstrated by the aggregation of melanosomes in flounder skin after intraperitoneal injection of the peptide. The number of MCH mRNA copies was greater in fish reared with a white background than in those reared with a black background. The MCH gene expression level in the brain was higher in fasted fish than in controls, indicating the association of MCH with food intake.2. We cloned two MCH receptors (MCH-R) from the barfin flounder. The expression of MCH-R1 was confined to the brain, while transcripts of MCH-R2 were detected in several tissues including the brain. The expression of MCH-R2 in eyed-sideskin was higher in fish reared with a black background than with a white background.3. In goldfish, cumulative food intake was decreased by intracerebroventricular injection of MCH, while it was increased by intracerebroventricular injection of MCH antiserum. The number of MCH immunoreactive somata in a part of the goldfish hypothalamus decreased significantly in fasted fish as compared with fed fish. These results indicate that MCH has a potential to function as an anorexigenic neuropeptide in goldfish.4. We cloned three POMC subtypes from the barfin flounder. The expression of POMC-A was confined to the pituitary, while transcripts of POMC-B and-C were detected in several tissues including the pituitary. Posttranslational processing of POMC of the pars distalis and pars intermedia in the barfin flounder pituitary differs from each other.5. Expressions of melanocortin 1 and 4 receptors were observed in the brain, eye-balls, testes, and skin of the barfin flounder. Melanocortin 4 receptor was also expressed in the liver, of which expression was increased by fasting. The results suggest the association of this receptor with energy homeostasis.