[Electroencephalographic study with buspirone, a novel nonbenzodiazepine anxiolytic, and its major metabolite, 1-(2-pyrimidinyl)piperazine (1-PP), in rabbits].

The electroencephalographic (EEG) effects of buspirone and its major metabolite, 1-(2-pyrimidinyl)piperazine (1-PP), were investigated in rabbits with chronic electrode implants, and the effects were compared with those of diazepam. Intravenous administration of buspirone at 0.1 to 1.0 mg/kg evoked an increase in the arousal EEG pattern period (low amplitude fast waves) in the cortical EEG and synchronization of the hippocampal theta waves with decreased voltages, whereas both 1-PP (0.5 to 2.0 mg/kg, i.v.) and diazepam (1.0 and 2.0 mg/kg) evoked an increase in the drowsy EEG pattern periods: high voltage slow waves and spindle bursts in the cortical EEG and desynchronization of the hippocampal theta waves. Buspirone at higher doses caused behavioral excitation in rabbits, whereas both 1-PP and diazepam produced sedation. Buspirone did not affect EEG arousal responses to both auditory stimulation (2,000 Hz, monotone) and electrical stimulation (100 Hz, 0.1 msec, 3-6 V) of the midbrain reticular formation or the posterior hypothalamus. However, 1-PP tended to inhibit the EEG arousal response to auditory stimulation but not brain stimulation, and diazepam markedly suppressed the responses induced by both stimulations. The recruiting response induced by centromedian thalamic stimulation at a low frequency (7 Hz, 0.1 msec, 4-8 V) was not affected by buspirone, 1-PP and diazepam. Neither buspirone nor 1-PP had an effect on the photic driving response to a flash light (2 Hz) in the occipital cortex of the rabbit, whereas the response was suppressed by diazepam. Both buspirone and 1-PP enhanced the duration of after discharges induced by electrical stimulation (50 Hz, 0.5 msec, 4-15 V) of the dorsal hippocampus, whereas diazepam markedly inhibited the afterdischarges. These results suggest that the EEG effect of buspirone is quite different to those of 1-PP and diazepam in qualitative aspects. It is also suggested that buspirone, unlike diazepam, is an effective anxiolytic drug without a sedative effect.