ASSOCIATIONAL AND NONASSOCIATIONAL MECHANISMS IN LOCOMOTOR SENSITIZATION TO THE DOPAMINE AGONIST QUINPIROLE

A pairing paradigm was employed to explore the contribution of associa tional mechanisms to the expression of sensitization to the dopamine a gonist quinpirole. Rats received ten quinpirole injections in the test environment (Group Paired) or in the home cage (Group Unpaired), and saline in the alternate environment. A third group received saline inj ections in both environments (Group Acute). Subjects received quinpiro le on the 11th injection as a test for locomotor sensitization, and sa line on the next injection as a test for conditioned activity. The ran ge of discriminative stimuli predicting a drug versus a non-drug injec tion was increased across three independent experiments in an effort t o detect a possible associational effect. Regardless of the strength o f discriminative stimuli, both Paired and Unpaired groups showed locom otor sensitization to 0.5 mg/kg quinpirole compared with the Acute gro up. However, the Paired group showed more locomotion than the Unpaired group in the last minutes of the sensitization test. With a lower sen sitizing dose of quinpirole (0.1 mg/kg) used in one experiment, only t he Paired group showed locomotor sensitization. For both doses, the Pa ired, but not the Unpaired groups showed conditioned locomotion. It is suggested that with moderate doses of quinpirole, expression of locom otor sensitization does not require drug-signalling cues though such s ignals may have a modulatory influence. With lower quinpirole doses, h owever, quinpirole sensitization is context-dependent.