Comparison of cocaine and procaine discriminative stimuli

The discriminative stimulus, abuse potential, and locomotor‐activating properties of cocaine have all been attributed to dopaminergic activity. Unexplained are findings that the local anesthetic, procaine, with little or no documented dopamine agonist activity, has stimulus properties similar to cocaine and is also self‐administered. The purpose of the work described here was to compare the discriminative stimulus properties of cocaine and procaine and the ability of procaine and other local anesthetics to induce rotational (circling) behavior in unilaterally 6‐hydroxydopamine‐lesioned rats. Rats were trained in a two‐lever, food‐reinforced, operant task to discriminate either cocaine (10 mg/kg, i.p.) or procaine (54.6 mg/kg, i.p.) from saline. Results show that cocaine and procaine have similar stimulus properties, administration of either resulting in partial generalization to the other. Cocainetrained animals generalized perfectly to the psychomotor stimulants amphetamine and methylphenidate. Haloperidol more effectively blocked cocaine than procaine. The alphaadrenergic blocker phentolamine was ineffective against either training drug. Apomorphine, caffeine, and nisoxetine yielded partial generalization to both of the training drugs. Upon acute administration, the local anesthetics other than cocaine showed no significant ability to induce rotation in lesioned rats.