Functions of melanin‐concentrating hormone in fish

Abstract

Melanin-concentrating hormone (MCH) was originally discovered in fish, in which it causes aggregation or concentration of melanin granules in melanophores, thus regulating body color. MCH is a cyclic neuropeptide synthesized as a preprohormone in the hypothalamus of all vertebrates. Mammalian MCH plays an important role as a neurotransmitter or neuromodulator in regulating food intake and energy homeostasis. MCH signaling system may involve in regulating food intake also in fish. This neuropeptide binds to G-protein-coupled seven transmembrane receptor[s] to mediate its functions. This article reviews MCH and MCH receptor signaling systems in body color change and food intake in fish.

Melanin-concentrating hormone projections to areas involved in somatomotor responses

“…The MCH neurons are also found in the incerto-hypothalamic area (IHy), an area that we have found to participate in the medial hypothalamic circuitry, and that is likely involved in the control of motivated behaviors (Sita et al, 2007). www.elsevier.com/locate/jchemneu In teleost fish, as well as in amphibians and reptiles, MCH has the effect of blanching the skin as part of an adaptive behavioral response (Kawauchi, 2006). However, in rodents, changes of MCH expression in obese animals and alteration in food intake following administration of MCH to normal animals suggest that the peptide participates in body weight regulation (Qu et al, 1996;Rossi et al, 1997;Flier and Maratos-Flier, 1998).…”

Identification of mRNAs coding for mammalian-type melanin-concentrating hormone and its receptors in the scalloped hammerhead shark Sphyrna lewini

“…In the teleost brain, MCH neurons are mainly located at the nucleus ventralis tuberis of the ventral hypothalamic area and project into the neurohypophysis [2,3,25,30], where MCH is released into general circulation [16]. In the mammalian brain, MCH neurons are localized in the lateral hypothalamic area and in the zona incerta of the dorsal hypothalamic area [7].…”

“…The distribution of melanin in melanocytes was observed with a transilluminant microscope. The melanophore index (MI) was calculated using the method described by Kobayashi et al [16], to evaluate pigment-aggregating activity of human MCH. The average MI from 10 melanophores represented the MI of each skin sample (N = 6).…”

“…In the neurohypophysis, MCH is involved in regulating release of pituitary hormones, such as a-MSH [13], gonadotropin [10], and somatolactin [9,43]. When the pituitary gland releases MCH into circulation, it induces pigment aggregation to the chromatophores in the skin, making the body color lighter [16]. Nevertheless, the MCH-induced pigment changes have only been found in some osteichthyes (bony fish), including teleosts [5].…”

PACAP system evolution and its role in melanophore function in teleost fish skin

“…(Oshima et al, 2001). Fish Mch is mainly secreted by the neurohypophysis and activates Mch-r2 that is coupled to the Gi-protein complex that inactivates adenylate-cyclase and signals via the inhibition of cellular cAMP levels (Hamamoto et al, 2011;Kawauchi, 2006). However, Mch actions in fish are not conserved and tilapia and catfish skin contain another receptor type, Mch-r1, that signals via cAMP and promotes and stimulates melanin dispersion suggesting that regulation of skin colour pattern in fish may be species dependent (Oshima et al, 2001).…”