Abstract
Summary
The effect of phenobarbital on locomotor activity was studied in mice for periods of 24 hours and in hamsters for 1–8 days. Doses of 100 to 150 mg/kg caused stimulation, 1 and 5 mg/kg doses were followed by suppression of activity, and 200 mg/kg resulted in a biphasic, suppressive-stimulant effect. Doses that caused stimulation were sufficiently toxic to induce ataxia of gait. The hyperkinetic response occurred after administration in daytime and at night. Artificial light failed to abolish the circadian rhythmic increase in activity at night in both treated and untreated animals. Repeated daily doses did not result in tolerance, but suppression of activity occurred on drug withdrawal.
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