ALTERATIONS OF PHYSOSTIGMINE-INDUCED YAWNING BY CHRONIC LITHIUM ADMINISTRATION IN RATS

The effect of chronic lithium pretreatment on physostigmine-induced ya wning was investigated in male rats. Intraperitoneal administration of physostigmine to rats induced yawning in a biphasic manner. However t he maximum response was obtained by 0.2 mg/kg of the drug. Intracerebr oventricular administrations of a putative M-1 and M-2 muscarinic rece ptor antagonists, pirenzepine and methoctramine decreased physostigmin e-induced yawning. Intraperitoneal administration of a non-selective m uscarinic receptor antagonist, atropine, also decreased the physostigm ine-induced yawning significantly Chronic lithium pretreatment (30 day s) reduced yawning induced by physostigmine. The inhibitory effect of pirenzepine, methoctramine and atropine on physostigmine-induced yawni ng increased in rats pretreated with chronic lithium. These findings i ndicate that yawning is induced by a central cholinergic mechanism and that chronic pretreatment of lithium may interact with the cholinergi c-induced behaviour.