Comparative behavioral effects of anticholinergic agents in cats: psychomotor stimulation and aggression

The effect on behavior of eight anticholinergic agents: atropine, scopolamine, trihexyphenidyl, biperiden, homatropine, eucatropine, hexocyclium and propantheline, injected into the cerebral ventricle (ICV) of the cat was investigated and compared. The anticholinergic agents evoked: (1) psychomotor stimulation such as miaowing, loud calling, restlessness, impelling locomotion, jumping, vacant staring, apprehension and loss of interest of the surroundings; (2) aggression, hissing, threat, attack, defense, fighting with paws and flight; (3) autonomic responses including mydriasis, tachypnea, dyspnea, licking, vomiting, salivation, micturition and defection; and (4) motor phenomena comprising scratching, ataxia, rigidity, tremor, weakness with adynamia or myoclonic jerks. Convulsions appeared only after ICV injections of atropine and homatropine. The most characteristic behavioral effect of anticholinergic agents was psychomotor stimulation accompanied by mild aggressive responses. The only exception was propantheline which caused a muscular weakness and adynamia. Atropine and scopolamine alone induced a dose-dependent impelling locomotion as well as fighting behavior. Carbachol and eserine injected intracerebroventricularly reversed the locomotion autonomic and motor phenomena produced by anticholinergic agents administered similarly. It is suggested that anticholinergic agents acting as partial agonists, can produce their behavioral effects through central cholinoceptive sites.