Effects of diazepam on somatosensory evoked potentials in rats at two different periods of day

The effects of diazepam (5 mg/kg i.v.) on somatosensory evoked potentials (SEPs) were investigated in rats in acute experiments. Generally an increase of the peak-latencies and a reduction of the amplitudes were observed immediately after diazepam (DZP) administration. An account was given of the differences in the DZP effect on SEP when the drug was applied at two different periods of day. The late cortical components were affected in both day and night, whereas the early and intermediate potentials were influenced by DZP only during the light period of day. The late N17 proved to be more sensitive to DZP in the night recordings. Our results suggest that the DZP effect on SEP in daylight conditions is more pronounced than that at night. The possible mechanisms responsible for this difference were discussed.