EFFECTS OF DIAZEPAM AND THE SPECIFIC BENZODIAZEPINE ANTAGONIST FLUMAZENIL ON SOMATOSENSORY EVOKED-POTENTIALS IN RATS

Changes in somatosensory evoked potentials were studied in 88 rats fol lowing intravenous injections of diazepam (0.5, 1 and 5 mg/kg) and flu mazenil (0.5 and 5 mg/kg). The antagonist effect of flumazenil against previously administered diazepam was evaluated by somatosensory evoke d potentials, when given in the same doses. Generally, a peak-latency increase and an amplitude reduction were observed after diazepam admin istration. The low dose of flumazenil led to similar changes in somato sensory evoked potentials. The higher dose of flumazenil resulted in a n immediate, short-lasting latency decrease of the late cortical poten tials and an amplitude reduction with a delay in its appearance. Accor ding to the obtained data, diazepam elicited a marked suppressive acti on mainly on the corticocortical processing of the sensor information with a milder effect on the thalamic level. Flumazenil showed some int rinsic activities with the low dose effects being benzodiazepine-like and the higher dose resulting in two overlapping opposite actions (ini tially stimulant and subsequently suppressive). The same flumazenil do ses, applied 30 min after injection of diazepam, were able to fully or partially reverse (with some dose differences) the diazepam-induced l atency prolongations, whereas flumazenil could not antagonize signific antly the diazepam effect on the amplitudes. This may be due to the gr eater influence of diazepam on the amplitudes.