Antagonism of apomorphine-induced pecking in pigeons.

Central nervous system stimulants, tranquillizers and other central nervous system depressants, antiemetics, antihistamine drugs and autonomic blocking agents were examined for their ability to prevent the pecking response in pigeons induced by apomorphine (250 mug/kg intramuscularly). Reduction in the proportion of positive responses or significant increase in the latent period of pecking were taken as the criterion of effectiveness. Protection was afforded by caffeine, lysergic acid diethylamide, morphine, rauwolscine, triflupromazine and yohimbine. In addition, a significant increase in latent period was produced by artane, pentobarbitone, benactyzine, 2-bromolysergic acid diethylamide, cyclizine, diphenhydramine, ergotoxine, hyoscine, promethazine, 5-(2-chloroethyl)-4-methylthiazole and trimethobenzamide. Most of these drugs influenced the pecking and emetic responses to apomorphine in an identical manner. It is possible that identical receptors may be concerned with apomorphine pecking (in pigeons) and emesis (in other species).