Sucrose intake and fasting glucose levels in 5-HT(1A) and 5-HT(1B) receptor mutant mice

Abstract

Serotonin (5-HT)(1A) and 5-HT(1B) receptors have been implicated in the incidence and treatment of depression in part through the examination of animals lacking these receptors. Although these receptors have been repeatedly implicated in ingestive behavior there is little information about how 5-HT(1A) and 5-HT(1B) receptor mutant mice react to solutions of varying palatability. In the present experiment male and female 5-HT(1A) and 5-HT(1B) mutant and wild-type mice were presented with increasing concentrations of sucrose using a two-bottle choice procedure. In addition fasting blood glucose levels were assessed. Both male and female 5-HT(1B) mutant mice drank more sucrose than WT mice but also consumed more water. Female, but not male, 5-HT(1A) mutant mice similarly showed increased sucrose consumption, but did not demonstrate increased consumption of water. In addition, the pattern of increased sucrose consumption over genotype and sex was related to fasting blood glucose concentrations such that levels in male 5-HT(1B) mutant mice were reduced relative to wild-type and 5-HT(1A) mutant males, but similar to those of females. The findings in 5-HT(1B) mutant mice emphasize the role of the 5-HT(1B) receptor in regulating ingestive behavior, whereas female sex hormones and 5-HT(1A) receptors may interact to alter sucrose consumption in 5-HT(1A) mutant mice. In addition, these findings may have implications for the role of these receptors in the incidence and treatment of depression since the intake of sucrose has been used as an index of anhedonia in animal models of depression and antidepressant efficacy.

Figure 1

Mean (+SEM) sucrose intake (mg/kg) for female (A) and male (B) wild-type (WT), 5-HT_1A, (1A−/−) and 5-HT_1B (1B−/−) mice. *; Significantly different from WT of same sex. #; Significantly different from 1B−/− of same sex. In male mice follow-ups to a significant main effects of genotype revealed that male 5-HT_1B^−/− mice drank more sucrose overall than WT male mice (p < .05).

Figure 2

Bars represent mean (+SEM) water intakes (mg/kg) for female (A) and male (B) wild-type (WT), 5-HT_1A, (1A−/−) and 5-HT_1B (1B−/−) mice. *; Significantly different from WT mice of same sex. #; Significantly different from 1B−/− mice of same sex.

Figure 3

Bars represent mean (+SEM) blood glucose ((mg/dl) for female (A) and male (B) wild-type (WT), 5-HT_1A, (1A−/−) and 5-HT_1B (1B−/−) mice. *; Significantly different male mice of the same genotype. #; Significantly different from WT mice of same sex. †; Significantly different from 1A−/− mice of same sex.