A sustained increase in the brain concentrations of neuroactive steroids was previously shown to induce Y1 receptor gene expression in the amygdala of Y1R/LacZ transgenic mice which harbour a construct comprising the murine Y1 receptor gene promoter and the lacZ reporter gene. We now investigated the effects of restraint stress on both the cerebrocortical concentrations of neuroactive steroids and Y1 receptor gene expression in the amygdala and hypothalamic paraventricular nucleus (PVN) of Y1R/LacZ transgenic mice. The cerebrocortical concentrations of allopregnanolone and allotetrahydrodeoxycorticosterone were significantly increased immediately after a 1-h exposure to restraint stress and had returned to control values within 30 min. Expression of Y1R/LacZ was increased in the amygdala and PVN 6 h after restraint. The 5alpha-reductase inhibitor finasteride, that prevented the increase in neuroactive steroid concentrations, did not block that in transgene expression induced by 1-h restraint. Daily exposure to restraint for 10 days also increased the cerebrocortical concentrations of neuroactive steroids but failed to affect transgene expression. Acute but not repeated restraint thus increases Y1 receptor gene expression in the amygdala and PVN, suggesting that tolerance develops towards this stressor. The effect of acute restraint is not mediated by the increase in the brain concentrations of neuroactive steroids but may rather reflect a ligand-induced increase in Y1 receptor gene transcription. Data support a role of Y1 receptors in the behavioural and neuroendocrine responses to stress.