Histidine-induced bizarre behaviour in rats: the possible involvement of central cholinergic system

Histidine injected intraperitoneally into rats in doses from 400 to 800 mg/kg induced a dose-dependent bizarre behaviour. The behaviour after histidine was similar to that observed after L-DOPA and peripheral decarboxylase inhibition. The bizarre behaviour was antagonized by chloropyramine, ketotifen, clemastine and promethazine, antagonists of histamine H1 receptors, with ED50's of 13.9, 14.2, 21.6 and 22.2 mg/kg, respectively. Cimetidine, an antagonist of histamine H2 receptors, injected intraventricularly at a dose of 100 micrograms, was without effect. The bizarre behaviour after histidine was not changed by antagonists of dopamine, noradrenaline and serotonin receptors, but it was blocked by atropine, indicating involvement of central cholinergic systems.