The effect of RO 60-0175 (RO; 3 mg/kg, i.p.) on 5-HT turnover under conditions of stress was determined in mice with genetic ablation of either GABA-B1a, GABA-B1b or GABA-Aα3 receptor subunit and in WT mice after pharmacological blockade of GABA-A or GABA-B receptors with bicuculline (8 mg/kg, i.p.) or phaclofen (2 mg/kg, i.p.), respectively. Results are presented as a percentage of the 5-HIAA/5-HT ratio in saline-treated mice of the same genotype (means ± S.E.M.; n= 4–8). * p≤0.05, ** p<0.01, one-tail Student’s t-test.