Pre-treated with a sub-threshold dose of MAPK inhibitor suppressed depression-like behaviour in neonatal DEX-treated animals. (a) In the given sub-threshold dose PD98059 did not alter the expression of depression-like behaviour in control group. The increased depression-like behaviour in DEX-treated animals was suppressed by the MAPK inhibitor. (b) Compared with the vehicle group (control), a sub-threshold dose of PD98059 the DEX group showed no significant different in locomotor activity. (c) There was no significant difference in retention of the rota-rod task among groups. Each vertical bar represents the Mean±s.e.m. for each group. **p < 0.01 compared with the corresponding group.