Failure of dexamphetamine to antagonise a cholinomimetic-induced hyperactivity

Rats that were treated with physostigmine (0.05 mg/kg) manifested marked hyperactive behaviour. A subsequent injection of dexamphetamine (2.0 mg/kg) did not antagonise the physostigmine-induced locomotor hyperactivity, whereas atropine (10 mg/kg) attenuated the hyperactive behaviour. Higher doses of physostigmine depressed the locomotory behaviour of rats. Carbachol and (ñ)-O-methyl-p-tyrosine did not significantly affect rats' locomotory behaviour. Implications of the results are discussed in terms of the aetiology of hyperkinesia (AU)