Differential effects of benzodiazepines on EEG activity and hypnogenic mechanisms of the brain stem in cats.

The effects of quazepam, flurazepam and diazepam (0.12-1 mg/kg i.v.) on cortical electroencephalogram (EEG) and EEG power spectra were studied in cats with lesioning at various levels of the brain stem (encéphale isolé, midpontine pretrigeminal and cerveau isolé preparations). In the encéphale isoleé, quazepam produced slow waves, spindles and power increases in the 0.5-14 Hz range. Flurazepam produced similar EEG activity but alternated with fast frequency rhythms (8-14 Hz) of moderate amplitude. Diazepam produced spindles superimposed on a continuous fast frequency background while the slow waves were not observed. In the midpointine cats, quazepam modified the desynchronized EEG only at the higher doses. It enhanced the fast rhythms (10-14 Hz) observed in controls. Flurazepam produced similar effects but to a great extent. EEG effects of diazepam were similar to those observed in the encéphale isolé. Thus, the midpontine transection precluded the appearance of the slow wave synchronization. None of the benzodiazepines affected the synchronized EEG of the cerveau isolé. It is suggested that quazepam and, at least in part, flurazepam may induce EEG synchronization and slow wave sleep by influencing hypnogenic mechanisms of the lower brain stem. Fast EEG patterns produced by diazepam and partially by flurazepam seemed unrelated to the sleep-inducing mechanisms while the activating mesencephalic system appeared to be involved.