Behavioral and electroencephalographic effects of lormetazepam were investigated in rats, mice and rabbits, in comparison with those of diazepam, nitrazepam and flurazepam. Locomotor activity of mice in an open-field situation was decreased with large doses of lormetazepam and diazepam, while it was increased with nitrazepam and flurazepam. The anticonflict effect of lormetazepam in rats was much more potent than those of diazepam, nitrazepam and flurazepam. In suppressing the muricide of olfactory bulbectomized and raphe lesioned rats, lormetazepam was more potent than diazepam, nitrazepam and flurazepam. Lormetazepam, diazepam and flurazepam prevented both maximal electroshock and pentetrazol convulsions in mice, the effects on the latter being much more potent than those on the former. Lormetazepam was more potent than diazepam and flurazepam in potentiating thiopental-, ether- and ethanol anesthesia, impairing rotarod performance and in muscle relaxant activity. In conscious rabbits with chronically implanted electrodes, lormetazepam induced a drowsy EEG pattern and suppressed the EEG arousal responses not only to auditory stimulation but also to electrical stimulation of the midbrain reticular formation or hypothalamus. Lormetazepam also inhibited afterdischarges induced by electrical stimulation of the hippocampus and amygdala. These results indicate that lormetazepam has pharmacological properties characteristic of benzodiazepines and that the activity is more potent than those of diazepam, nitrazepam and flurazepam.
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