Apomorphine-induced pecking in pigeons.

Apomorphine produced persistent pecking in pigeons, the latent period, intensity and duration of which were related to the dose. The ED50 was estimated as 78.1+/-11.1 mug./kg. On chronic administration of apomorphine there was a significant decrease in latent period and weight which quickly returned to normal on stopping the drug. No conditioning and no tolerance were observed. The uncertain emetic effect of apomorphine in pigeons has been confirmed. Ten other centrally acting agents tested (caffeine, cocaine, 5-hydroxytryptamine, lysergic acid diethylamide, methamphetamine, morphine, nalorphine, pentylenetetrazol, strychnine, and yohimbine) failed to produce similar effects in pigeons.