Neuromedin U (NMU) is a bioactive neuropeptide, highly distributed in the 
gastrointestinal tract and the central nervous system. NMU has various 
physiological functions related to feeding behavior, energy metabolism, stress 
responses, circadian rhythmicity and inflammation. Recently, several reports 
indicate that the central NMU system plays an important role in the reward 
systems in the brain. However, the underlying molecular mechanisms are not yet 
fully defined. In this study, we found that some of cocaine-induced c-Fos 
immunoreactive cells were co-localized with NMU in the nucleus accumbens (NAc), 
caudate putamen (CPu), and basolateral amygdala (BLA), which are key brain 
regions associated with the brain reward system, in wild type mice. Whereas, a 
treatment with cocaine did not influence the kinetics of NMU or NMU receptors 
mRNA expression in these brain regions, and NMU-knockout mice did not show any 
higher preference for cocaine compared with their control mice. These results 
indicate that cocaine has some effect on NMU expressing neurons related to the 
brain reward system, and this suggests NMU system may have a role on the brain 
reward systems activated by cocaine.