Midazolam and somatosensory evoked potentials.

The effect of midazolam, a water-soluble benzodiazepine, on the somatosensory evoked potentials (SEPs) following strong electrical stimulation of the upper lip, was investigated in Wistar albino rats. SEPs were recorded from the surface of the skull in the contralateral temporal area. A computer was used to obtain the averaged SEPs. The rats received intraperitoneal dosages of 1.25, 2.5, or 5.0 mg/kg of midazolam, or physiological saline. Relative amplitudes of the P(1)N(1) wave were reduced significantly after midazolam injection. Amplitude recovered to the control level about 120 min after the injection in the 1.25 mg/kg group. In 2.5 and 5.0 mg/kg groups, midazolam-induced suppression did not recover within 120 min. No significant differences were found in the latencies of P(1) and N(1) before and after midazolam injection. It is suggested that midazolam has a mild analgesic effect due to central suppression of the pain perception following noxious stimuli.