PHARMACOLOGICAL CHARACTERIZATION OF THE ENHANCEMENT OF APOMORPHINE-INDUCED GNAWING IN MICE BY COCAINE

The present study was designed to provide additional information on th e behavioral and pharmacological mechanisms associated with the augmen tation of apomorphine-induced gnawing in C57BL/6J mice. (-)-Cocaine en hanced apomorphine-induced gnawing at doses devoid of effects on gnawi ng when given alone. The effect was stereoselective, with (+)-cocaine devoid of activity in this test. Peripheral synapses may also not be c ritical to the cocaine enhancement, as cocaine methiodide, a charged s pecies, was also without effect. The local anesthetic actions of cocai ne were evaluated with lidocaine, a local anesthetic without prominent dopaminergic actions. Like (-)-cocaine, lidocaine augmented the gnawi ng response to apomorphine without increasing climbing or gnawing when given alone, (+)-Amphetamine enhanced apomorphine-induced gnawing but only at a high dose that increased gnawing by itself. The selective d opamine uptake blocker, GBR 12909, augmented apomorphine-induced gnawi ng without increasing gnawing when given alone; however, unlike cocain e or lidocaine, GBR 12909 increased climbing at doses that augmented t he gnawing response. These data indicate that the cocaine-augmented gn awing response to apomorphine does not appear to be the result of psyc homotor stimulation per se. Rather, this effect may be due to blockade of dopamine uptake and/or the local anesthetic actions of cocaine.