Drug effects in a novel biphasic writing syndrome induced by acetylcholine in mice.

The writing induced in mice by i.p. administration of 3 mg/kg acetylcholine chloride showed a biphasic response with time. The primary phase of 1-15 sec after acetylcholine appeared to be the result of nicotinic receptor stimulation. The secondary phase from 30 sec following acetylcholine was selectively suppressed by anti-inflammatory agents and by atropine, while centrally acting analgesicw, other strong central nervous system drugs and ganglion blockers suppressed both phases of writhing to an equal extent. The narcotic partial agonists significantly suppressed primary writhing more readily. The method appears to be of value in testing new pharmacological agents.