ABSTRACT
RATIONALE: Flumazenil, a competitive antagonist of benzodiazepine receptors (BZRs), has been used as a probe to detect effects of putative endogenous ligands for BZRs in anxiety. Flumazenil is renowned for its highly inconsistent behavioral effects. OBJECTIVE: To ascertain effects of flumazenil in the social conflict test in mice, which provides complex measures for prediction of anxiolytic and anxiogenic activity of drugs in behaviorally different groups of animals. METHODS: Singly housed male mice treated with flumazenil (5, 20 or 80 mg/kg i.p.) or vehicle were paired with untreated non-aggressive group-housed male mice in a novel cage. Behavior was analyzed from video tapes of the social interactions in three populations of mice: timid (n=21), aggressive (n=11), and sociable (n=7). Levels of gamma-aminobutyric acid (GABA) were measured in vivo in the prefrontal cortex. RESULTS: Flumazenil reduced timid (defensive-escape) and increased locomotor activities in timid mice. The drug reduced aggressive and increased sociable (social investigation) activities in aggressive mice. These behavioral changes were produced at the lowest dose of flumazenil tested (5 mg/kg) and were not increased further by higher doses of the drug (20 mg/kg or 80 mg/kg). A tendency to increased timidity was found after flumazenil in sociable mice. Concentrations of GABA were markedly higher in the prefrontal cortex of sociable mice than in timid or aggressive mice. CONCLUSIONS: Flumazenil produced moderate anxiolytic-like behavioural changes and a slight anxiogenic-like effect. The present data might be reflecting antagonism of corresponding endogenous BZR ligands. However, these putative ligands seem to exert only modest modulatory influence.
