Modification of apomorphine-, physostigmine- and pilocarpine-induced yawning after long-term treatment with neuroleptic or cholinergic agents.
Chronic treatment with haloperidol, physostigmine and scopolamine exerted different effects on the frequency of yawning induced by apomorphine (0.25 mg/kg, i.p.), physostigmine (0.2 mg/kg, i.p.) and pilocarpine (4 mg/kg, i.p.) as compared with chronic treatment with saline. Haloperidol decreased the apomorphine- and physostigmine-induced yawning but not the pilocarpine-induced yawning. Physostigmine reduced only the pilocarpine-induced yawning without affecting the apomorphine- and physostigmine-induced yawning. However, physostigmine showed the most rapid onset- and peak-time of yawning induced by a high dose of physostigmine (0.75 mg/kg, i.p.) as well as that of pilocarpine (8 mg/kg, i.p.), and potentiated apomorphine (1 mg/kg, i.p.)-induced stereotypy, as compared with that observed in the saline group. Scopolamine potentiated the physostigmine- and pilocarpine-induced yawning but not the apomorphine-induced yawning. A single pretreatment with scopolamine (0.5 mg/kg, i.p.), however, depressed these yawning responses. The results suggest that yawning induced by physostigmine, but not by pilocarpine, may be modified by long-term treatment with haloperidol. The stereotypy mediated by the postsynaptic dopaminergic system, but not the yawning mediated by the presynaptic system, may be altered by chronic treatment with physostigmine, while long-term treatment with scopolamine seems to produce a supersensitivity to cholinergic receptors.