Schematic experimental protocol. Rats were treated with VPA or vehicle (saline, i.p.) for 4 days (30 min before each FS and 1 day after FS). Rats swam for 10 min on the first day and 20 min on the next 2 days. The behavioral tests for thermal withdrawal latency and mechanical withdrawal threshold were assessed before (baseline) and after FS. d, day; T, Thermal withdrawal latency; M, mechanical withdrawal threshold; FS, forced swim; i.p., intraperitoneal; i.t., intrathecal injection. Visceromotor response (VMR) experiments were conducted in a separate group.