Neuronal histamine regulates food intake, adiposity, and uncoupling protein expression in agouti yellow (Ay/a) obese mice

Hypothalamic neuronal histamine and its H-1 receptor (H-1-R) form a part of the leptin-signaling pathway in the brain and have been shown to regulate body weight and adiposity in diabetic (db/db) and diet-induced obese mice by affecting food intake and uncoupling protein mRNA expression. The pro-opiomelanocortin (POMC) melanocortin-4 receptor (MC-4R) is also important for leptin signaling. The present study had two aims: first, to clarify the antiobesity action of neuronal histamine in agouti yellow (A(y)/alpha) obese mice, a model of obesity in which POMC/MC-4R signaling is disrupted by blockade of MC-4R and second, to investigate the functional relationship between neuronal histamine and POMC/MC-4R signaling. Central administration of histamine into the lateral cerebroventricle decreased cumulative food intake and body weight in A(y)/alpha obese mice. Histamine treatment also decreased mRNA expression of ob gene in epididymal white adipose tissue and up-regulated uncoupling protein 1 mRNA expression in brown adipose tissue. These effects were attenuated in A(y)/alpha obese mice with histamine H-1-receptor (H-1-R) knockout. Histamine treatment induced c-Fos-like immunoreactivity in both paraventricular and arcuate nucleus. There was no significant difference in histamine-induced c-Fos-like immunoreactivity in the hypothalamus between A(y)/alpha obese mice and lean littermates, indicating histamine signaling was not disrupted at the hypothalamic level in A(y)/alpha obese mice. These results suggest that neuronal histamine have an anti-obese action, even in A(y)/alpha obese mice despite a deficiency in POMC/MC-4R signaling. In addition, it appears that the histamine H-1-R signaling pathway may be independent or downstream of the POMC/MC-4R signaling.