Effects of cholinergic and GABAergic drugs on apomorphine-induced gnawing behavior in rats

The effects of cholinergic and GABAergic agonist and antagonist were studied on the apomorphine-induced gnawing behavior in rats. Physostigmine (0.5 mg/kg) decreased the biting scores, whereas atropine (5 mg/kg) had an opposite effect. Picrotoxin potentiated the physostigmine inhibitory action on gnawing responses. This inhibitory gnawing effect was antagonized by prior treatment with atropine. Pretreatment with amino-oxyacetic acid (25 mg/kg) also potentiated the inhibitory effect of physostigmine on gnawing behavior in animals. Such an additive inhibitory response could be antagonized by simultaneous pretreatment with cholinergic and GABAergic blockers such as atropine and picrotoxin, respectively. These findings indicate that the modulatory action of cholinergic neurons on DA system is probably influenced by changes in the GABAergic system.