Oral Monosodium Glutamate Differentially Affects Open-Field Behaviours, Behavioural Despair and Place Preference in Male and Female Mice

Abstract

Monosodium glutamate (MSG) is a flavour enhancer which induces behavioural changes in animals. However the influence of sex on the behavioural response to MSG has not been investigated. The sex-differential effects of MSG on open-field behaviours, anxiety-related behaviour, behavioural despair, place-preference, and plasma/brain glutamate levels in adult mice were assessed. Mice were assigned to three groups (1-3), based on the models used to assess behaviours. Animals in group 1 were for the elevated-plus maze and tail-suspension paradigms, group 2 for the open-field and forced-swim paradigms, while mice in group 3 were for observation in the conditioned place preference paradigm. Mice in all groups were further assigned into five subgroups (10 males and 10 females), and administered vehicle (distilled water at 10 ml/kg) or one of four doses of MSG (20, 40, 80 and 160 mg/kg) daily for 6 weeks, following which they were exposed to the behavioural paradigms. At the end of the behavioural tests, the animals were sacrificed, and blood was taken for estimation of glutamate levels. The brains were also homogenised for estimation of glutamate levels. MSG was associated with a reduction in locomotion in males and females (except at 160 mg/kg, male), an anxiolytic response in females, an anxiogenic response in males, and decreased behavioural despair in both sexes (females more responsive). Postconditioning MSG-associated place-preference was significantly higher in females. Plasma/ brain glutamate was not significantly different between sexes. Repeated MSG administration alters a range of behaviours in a sex-dependent manner in mice.