ENVIRONMENTAL AND BEHAVIORAL COMPONENTS OF SENSITIZATION INDUCED BY THE DOPAMINE AGONIST QUINPIROLE

Chronic intermittent injection of quinpirole (0.5 mg/kg) to rats in a large non-standard open field (mirrored glass table without walls, 160 x 160 cm and 60 cm high) induces pronounced behavioral sensitization characterized by a 6-fold increase in locomotor distance and increased rigidity of travel along the same routes (path stereotypy). Experimen t 1 showed that equivalent treatment in the home cage induces much les s sensitization of locomotor distance and no sensitization of path ste reotypy, as evidenced by a test in the open field. In Experiment 2, tr ansferring rats sensitized in one open field to a novel open field res ulted in a 50% loss of sensitized locomotor distance and a virtual los s of sensitized path stereotypy. In Experiment 3, rotating the open fi eld in relation to room cues did not affect sensitized responding, sug gesting that the behavior is organized in relation to distal rather th an local (open field) cues. Finally, an injection of saline in the sen sitized environment failed to elicit conditioned locomotion (Experimen t 4). These results are taken to indicate that the control of sensitiz ation to quinpirole has components that are environment independent, b ehavior specific, and context dependent, each having a relatively diff erent contribution and mechanism. It is suggested that under the exper imental conditions of this study, the relative contributions to quinpi role sensitization were 50% for the context-dependent component, 30% f or the behavior-specific component, and 20% for the environment-indepe ndent contribution. The mechanism for the context-dependent component may be related to development of path stereotypy and involve spatial l earning.