Environmental influences on behavioural sensitization to the dopamine agonist quinpirole.

A runway was used to measure locomotor responses to quinpirole (200µg/kg), in rats. The locomotor stimulant effect of quinpirole increased progressively over successive trials at 3-day intervals. Animals administered quinpirole in the home cage were also sensitized, but to a lesser degree than animals tested in the runway following quinpirole injections. Exposure to an open field, following quinpirole injections, sensitized responsiveness in the runway to an extent comparable to that seen following runway exposure. Animals exposed to a movable running wheel, following quinpirole injections, were more sensitized to the effect of quinpirole in the runway than animals exposed to a locked running wheel. The results suggest that the extent of sensitization to quinpirole is determined by the behaviour elicited by the drug, rather than the environment in which it is administered. An operant conditioning model is proposed to account for these effects.