Isolation and characterisation of four cDNAs encoding neuromedin U (NMU) from the brain and gut of goldfish, and the inhibitory effect of a deduced NMU on food intake and locomotor activity

In rodents, neuromedin U (NMU; U for its original effects examined in the uterus) is a multifunctional neuropeptide implicated in the regulation of the circulatory and digestive systems and energy homeostasis, especially appetite. However, there is no available information on the nature and physiological roles of NMU in fish. Therefore, we attempted to isolate and characterise transcripts encoding NMU from the brain and gut of the goldfish, and to examine the involvement of NMU in the regulation of feeding behaviour in this species. We identified four cDNAs encoding three NMU orthologs from the brain and gut. Putative peptides consisting of 21, 25 and 38 amino acid residues (NMU-21, NMU-25 and NMU-38) were deduced from their nucleotide sequences. Two mRNAs for NMU-25 were strongly expressed in the gut and weakly expressed in the brain and testis. By contrast, mRNA for NMU-21 was strongly expressed in the brain and weakly expressed in the peripheral tissues. Expression of mRNA for NMU-38 was weakly expressed only in the brain. Therefore, we examined the effect of feeding status on the expression of NMU-21 mRNA in the brain. Fasting for 7days induced a significant decrease in the expression levels of NMU-21 mRNA in the brain. We also synthesised NMU-21 after deducing its C-terminal amide from the NMU-21 mRNA, and then investigated the effect of intracerebroventricular (i.c.v.) administration of NMU-21 on food intake and locomotor activity in the goldfish. NMU-21, injected i.c.v., suppressed food intake and locomotor activity in a dose-dependent manner. These results suggest that NMU orthologs exist in fish, and that the NMU-21 deduced from them can potently inhibit food intake and locomotor activity in goldfish.