Male and female 5-HT1B receptor knockout mice have higher body weights than wildtypes

5-HT1B receptors have a regulatory role in serotonergic activity and influence feeding behavior and body weight. Because the absence of 5-HT1B receptors may cause changes in this regulation, body weight was measured in male and female 5-HT1B receptor knockout (5-HT1B KO) and wildtype (WT) mice from weaning until the age of 30 weeks. In both genders, 5-HT1B KO mice had a higher body weight than WT mice (17% and 9%, respectively). Body weight was significantly higher for males over the entire period and for females from Week 18 onwards. Absolute food and water consumption were related to body weight. However, relative to body weight, males consumed more than females. 5-HT1B KO males drank strikingly more water. Housing mice singly reduced food and water intake in males, but not in females. Plasma leptin levels and most organ weights did not differ between genotypes, indicating that higher body weight in 5-HT1B KO mice is not related to obesity. Relative to body weight, brains and adrenals were larger in females, while heart and liver were smaller. Kidneys were smaller in females, but larger in 5-HT1B KO mice, while lungs showed opposite effects. Spleen and testes were smaller in 5-HT1B KO mice. Although 5-HT1B KO males are more aggressive, testosterone levels were not different from WT mice. Basal corticosterone levels were similar in all groups and increased in response to mild stress, particularly in females. Lifelong absence of 5-HT1B receptors in mice resulted in clear phenotypic differences in body weights and food and water intake. Lacking this receptor increases body growth, without signs of obesity. A potential genetic background effect influencing this phenotype is discussed. (C) 2001 Elsevier Science Inc. All rights reserved.