Sleep deprivation has been shown to affect the production of steroid hormones in peripheral steroidogenic organs, but little is known about the influence of sleep disturbance on the metabolism of steroid hormones in the brain. To elucidate a possible association of the sleep-wake cycle with brain neurosteroid metabolism, the influence of short-term sleep disturbance on the expression of mRNA encoding steroid 5alpha-reductase, the enzyme converting progesterone and other steroid hormones to their neuroactive 5alpha-reduced metabolites, was investigated. Rats were first subjected to non-selective disturbance of the sleep-wake cycle, and the expression of steroid 5alpha-reductase mRNA in rat hippocampus and brainstem was determined using a semi-quantitative one-step RT-PCR technique. Non-selective disturbance of the sleep-wake cycle resulted in the elevation of 5alpha-reductase mRNA levels in the brainstem, but not in the hippocampus, and the elevated mRNA expression returned to the basal levels after a short period of the sleep recovery. Further studies showed that selective REM sleep deprivation significantly elevated 5alpha-reductase mRNA levels in both hippocampus and brainstem, thus proposing the possibility that REM sleep reduction may largely contribute to the elevation of steroid 5alpha-reductase mRNA levels observed during short-term disturbance of the sleep-wake cycle. Since the enhancement of steroid 5alpha-reductase gene expression may result in the elevation of neuroactive 5alpha-reduced steroid production in the brainstem, the findings presented here provide further evidence for suggesting that neuroactive steroids may play a physiologically important role in the neuronal network for REM sleep initiation and maintenance.