Pharmacologic studies of central actions of zopiclone: influence on brain monoamines in rats under stressful condition.

In order to investigate the central action of zopiclone, the rat brain was divided into 8 regions and the changes in monoamines (MA) in each region were examined. The effect of zopiclone on stress was also examined from changes in brain monoamines under electro-footshock stress load in comparison with that of nitrazepam and flurazepam. The animals were decapitated at 1 h after administration of zopiclone, nitrazepam and flurazepam at each dose of 1 and 10 mg/kg (p.o.). No changes in MA at each region of the brain were noted, but the metabolite, homovanillic acid (HVA) was reduced at the cortex, hippocampus, hypothalamus and cerebellum. 5-hydroxyindoleacetic acid (5-HIAA) was reduced at the amygdala. Noradrenaline (NA) turnover accelerated by electro-footshock stress load was inhibited by zopiclone. From the results of this experiment, it was found that the effects of zopiclone on brain MA were similar to those of nitrazepam and flurazepam: inhibition of 5-HT turnover at the amygdala was common to these three compounds. This result suggests that zopiclone has similar pharmacological properties to benzodiazepines as an antianxiety agent.