Effects of phenobarbital sodium on spontaneous motor activity

Utilizing a latin square design, rats were injected with 80, 40, 20, 10, 5 and 0 (saline control) mg/kg phenobarbital sodium prior to assessing spontaneous motor activity. Activity was found to be related to drug dose by an inverted-U shaped function, with maximum activity being observed subsequent to receiving 20 mg/kg. The relationship was reliable across Ss and from replication to replication.