Stress affects synaptic plasticity and may alter various types of behaviour, including anxiety or memory formation. In the present study, we examined the effects of acute stress (1 h restraint with or without tail-shock) on mRNA levels of a plasticity-related serine protease neuropsin (NP) in the hippocampus using semiquantitative RT-PCR and in situ hybridization. We found that NP mRNA expression was dramatically increased shortly after exposure to the acute restraint tail-shock stress and remained at high level for at least 24 h. The level of NP mRNA would be correlated to the elevated plasma concentration of the glucocorticoid corticosterone (CORT) and to the stress intensity. Application of CORT either onto primary cultured hippocampal neurons (5 nM) or in vivo to adrenalectomized (ADX) mice (10 mg/kg B.W., s.c.) mimicked the effect of stress and significantly elevated NP mRNA. These results suggest that the upregulation of NP mRNA after stress is CORT-dependent and point to a role for neuropsin in stress-induced neuronal plasticity.