Abstract
EEG effects of hydroxyzine were investigated in unanesthetized rabbits with chronic electrode implants. A comparison was then made with the effects of diazepam and chlorpromazine. Hydroxyzine, in doses of 2 ?? 5 mg/kg i.v., caused a drowsy pattern in spontaneous EEG, with behavioral sedation; i.e. high voltage slow waves and spindle bursts increased in EEG of the neocortex and amygdala, while the hippocampal theta rhythm was desynchronized. These effects of hydroxyzine were qualitatively similar even at doses of 10 ?? 15 mg/kg i.v., but the animals occasionally exerted behavioral arousal; i.e. a dissociation was observed between EEG and behavior. The EEG arousal responses to auditory as well as electric stimulation of the mesencephalic reticular formation, the posterior hypothalamus and the centro-median thalamic nucleus were markedly depressed by hydroxyzine and diazepam, while chlorpromazine showed little effect on the arousal response to mesencephalic reticular stimulation. The photic driving response elicited by flash light on the visual cortex was slightly depressed by hydroxyzine. The recruiting response was slightly enhanced by hydroxyzine and chlorpromazine, while it was depressed by diazepam. The hippocampal and amygdaloid afterdischarges were prolonged in duration by hydroxyzine at doses of 2 ?? 5 mg/kg i.v., but were rather depressed at doses of 10 ?? 15 mg/kg i.v. These after-discharges were potentiated by chlorpromazine at doses of 2 ?? 5 mg/kg i.v. and were depressed by diazepam at doses of 1 ?? 5 mg/kg i.v.. respectively.
