Temperature,food intake,and locomotor activity effects of a 5-HT3 receptor agonist and two 5-HT3 receptor antagonists in rats

This study investigated three physiologic functions known to be modulated by serotonin — temperature, food intake and locomotor activity — using the 5-HT₃ receptor agonist,m-chlorophenylbiguanide (m-CPBG), and two 5-HT₃ antagonists, MDL-72222 and ondansetron. m-CPBG produced dose-dependent elevations in rectal temperature. MDL-72222, which had no effects on temperature when given alone, significantly attenuated m-CPBG-induced hyperthermia. Food intake in food-deprived rats was reduced during the first hour by the highest dose of m-CPBG. Food intake was also dose-dependently reduced by MDL-72222; m-CPBG plus MDL-72222 led to greater reductions in food intake. Food intake in freely fed rats was unaffected by m-CPBG or MDL-72222. Locomotor activity was unaffected by m-CPBG, but was dose-dependently reduced by MDL-72222, an effect which may have contributed to its hypophagic effects. Ondansetron, used in ten-fold lower doses than MDL-72222, was inactive in all of these paradigms. These data: (1) provide some evidence for 5-HT₃ receptor-mediated changes in temperature; (2) are in agreement with two prior studies which reported locomotor activity reductions following 5-HT₃ antagonists; but (3) do not support an important role for 5-HT₃ receptors in the regulation of food intake in rats.