Brain-derived serotonin regulates appetite through the Htr1a and Htr2b receptors expressed in arcuate neurons. (A) Expression analysis of Htr1a in WT and Htr1a_Pomc^−/− hypothalamus by in situ hybridization compared with Pomc-1 in arcuate (Arc) nuclei (outlined by dashed line; experiment was performed using three different brains for each group). Bars, 500 µm. (B) Measurement of food intake (grams) over 12 and 24 h in WT, Htr1a_Pomc^+/−, and Htr1a_Pomc^−/− mice (n = 6 for each group). (C) BW (grams) analysis in WT, Htr1a_Pomc^+/−, and Htr1a_Pomc^−/− mice at 3 and 6 mo of age (n = 6 for each group). (D) Measurement of food intake (grams) over 12 and 24 h in WT (n = 6) and Htr1a;2b_Pomc^−/− (n = 4) mice. (E) Quantitative PCR analysis of Mc4r, Pomc-1, Cart (Cocaine and amphetamine regulated transcript), Mch (Melanin-concentrating hormone receptor 1), and Hyp (hypocretin) in WT (n = 8), Htr1a_Pomc^−/− (n = 4), and Htr1a;2b_Pomc^−/− (n = 4) hypothalami. Data shown are representative of three independent experiments. (F and G) Measurement of food intake (grams) over 12 and 24 h in WT (F) and quantitative PCR analysis of gene controlling appetite in WT mice infused with vehicle (n = 6) and WT (n = 6) and Htr1a;2b_Pomc^−/− (n = 6) mice infused by leptin (4 ng/h) for 7 d (G). Data shown are representative of two independent experiments. For all experiments: *, P < 0.05; **, P < 0.01 (Student’s t test). Error bars represent SEM.