This study was conducted to clarify the role of serotonin (5-hydroxytryptamine, 5-HT) 2C receptor (5-HT2CR) signaling during novelty-induced hypophagia in aged mice. Male C57BL/6J mice [6-week-old (young) and 79-80-week-old (aged) mice] were exposed to a novel environment, and its effects on feeding behavior, stress hormones, and appetite-related factors were examined. Exposure of aged mice to a novel environment suppressed food intake and increased corticosterone secretion. These responses were marked compared with those in young mice. The expression in hypothalamic corticotropin-releasing factor (CRF), pituitary CRF1R and proopiomelanocortin mRNA in aged mice exposed to a novel environment was increased or tended to increase, compared to control mice. 5-HT2CR antagonist, SB242084 or rikkunshito administration attenuated the decrease in food intake and increased stress hormone levels in aged mice exposed to the environmental change. The 5-HT2CR mRNA expression in paraventricular nucleus was significantly enhanced, when aged mice was exposure to the novel environment. Thus, novelty-induced hypophagia in aged mice resulted, at least in part, from up-regulated hypothalamic 5-HT2CR function. In conclusion, 5-HT2CR signaling enhancement and the subsequent activation of the CRF neuron were involved in novelty-induced hypophagia in aged mice, and the 5-HT2CR antagonists offer a promising therapeutic option for depression.
Keywords: 5-HT(2C)R; Aged; Food intake; Novelty; Rikkunshito.
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