Alteration of sweet taste receptor expression in circumvallate papillae of mice with decreased sweet taste preference induced by social defeat stress.

Anhedonia is a key diagnostic symptom and central feature of depression symptomatology, but the underlying mechanism remains unknown. In this study, we investigated whether the decrease of sweet taste preference, anhedonia-like behavior in experimental animals, was accompanied by alteration of sweet taste receptor expression in circumvallate papillae (CP) of social defeat stress (SDS)-subjected mice. By subjecting to 10-d SDS, male BALB/c and C57BL/6J mice with decreased sociability in a social interaction test were defined as SDS-susceptible ones, and they exhibited a depressive-like behavior in a forced swim test. In SDS-susceptible BALB/c mice, a two-bottle choice test with a sucrose solution revealed a reduction of sweet taste preference, while expression of sweet taste receptors, T1R2 and T1R3, in their CP was elevated, and the morphology of taste buds and numbers of type II-taste cells were not changed. In CP of SDS-susceptible C57BL/6J mice without a decrease of sweet taste preference, in contrast, there was no alteration of sweet taste receptor expression. Together with the finding that the body weight gain of SDS-susceptible BALB/c mice was apparently less than that of control ones, differing from the case of SDS-susceptible C57BL/6J ones, it is suggested that expression of sweet taste receptors in CP of SDS-susceptible BALB/c mice with decreased sweet taste preference might be upregulated to compensate for the stress-induced increase of energy expenditure.