Hypothalamic TRH Mediates Anorectic Effects of Serotonin in Rats

Expression of 5HT receptors and effects of 5HT, PKA, and PKC inhibitors on intracellular second messengers’ content and in pro-TRH mRNA levels in mHypoA-2/30 cells. A, 5HT_1A, 5HT_2C, and 5HT₆ receptors basal mRNA expression and pro-TRH mRNA levels in cell cultures treated with vehicle or different concentrations of 5HT for 24 h. Data represent the mean ± SEM of the mRNA levels expressed in arbitrary units (n = 3 wells/treatment). One-way ANOVA of pro-TRH mRNA expression showed a significant effect of treatment: F_(2,9) = 7.478, *p < 0.05 versus veh, ^{^}p < 0.01 versus 5HT 10 μm; (B) pCREB and (C) pERK1/2 content in cell cultures treated with vehicle or 5HT (100 μm) during 5 min, with the PKA inhibitor H89 (PKAi, 10 μm) or the PKC inhibitor chelerythrine chloride (PKCi, 1 μm) for 1 h, or with the PKAi or PKCi for 1 h and then with 5HT for 5 min (n = 4–5 wells/treatment). Values are expressed as percent of change versus vehicle-treated cultures’ values (100%). For pCREB content, the two-way ANOVA showed a significant effect of 5HT: F_(1,40) = 5.25, p < 0.05, or of treatment with inhibitors: F_(2,40) = 13.65, p < 0.001; *p < 0.05, **p < 0.01 versus veh, ⁺p < 0.05 versus 5HT. For pERK1/2, the two-way ANOVA showed a significant effect of 5HT: F_(1,38) = 4.45, p < 0.05, or of treatment with inhibitors: F_(2,38) = 27.25, p < 0.0001 and an interaction between inhibitors and serotonin treatments: F_(2,38) = 8.44, p < 0.0001; *p < 0.05, ****p < 0.0001 versus veh, ⁺⁺p < 0.01, ⁺⁺⁺p < 0.001 versus 5HT. D, pro-TRH mRNA expression in cell cultures treated with vehicle, 5HT (100 μm), PKAi (10 μm), PKCi (1 μm), or PKAi or PKCi and 5HT for 24 h (n = 5–10 wells/treatment). Data are expressed as the mean ± SEM of the fold change compared with vehicle values (1). The two-way ANOVA showed a significant effect of 5HT: F_(1,43) = 10.27, p < 0.01, or inhibitors treatment: F_(2,43) = 3.30, p < 0.05; **p < 0.01 versus veh; ^ɣp < 0.05 versus PKAi. PKA: protein kinase A, PKC: protein kinase C, pCREB: phosphorylated cAMP response element binding protein, pERK: phosphorylated extracellular signal regulated kinase, SEM: standard error of the mean, veh: vehicle, 5HT: serotonin.

Daily body weight and food intake registers. Body weight (A) and food consumption (B) in C, DIA and FFR rats from 0 to 5d. Data are expressed as the mean ± SEM in grams, n = 10 per group. For body weight the one-way repeated measures ANOVA showed differences through time F_(5,162) = 5.436, p < 0.001, between groups: F_(2,162) = 126.434, p < 0.001 and a significant interaction between time and groups: F_(10,162) = 3.139, p < 0.001. For food intake, the one-way repeated measures ANOVA showed a significant effect of time: F_(2,162) = 66.219, p < 0.001; of the interaction between time and groups: F_(10,162) = 2.091, p < 0.05). *p < 0.05, **p < 0.01, ***p < 0.001 DIA versus C rats. ⁺p < 0.05, ⁺⁺p < 0.01, ⁺⁺⁺p < 0.001 FFR versus C rats. SEM: standard error of the mean, C: control, DIA: dehydration-induced anorexia, FFR: forced-food restriction.