Environmental modulation of both locomotor response and locomotor sensitization to the dopamine agonist quinpirole

The study tested whether differences in locomotor activation during chronic treatment result in differential behavioral sensitization induced by the D2/D3 dopamine agonist quinpirole. One group of rats received repeated injections of quinpirole in their home cage and another group received this treatment in an alternate environment of similar size. In the home cage, quinpirole induced less locomotion than in the non-home environment. When tested in activity monitors at the end of chronic treatment, the home cage group showed less sensitized locomotion to quinpirole than the non-home cage rats. Thus, the extent of locomotor sensitization to quinpirole appears to be related to the amount of locomotion characteristic of the training environment. Such differential sensitization may reflect a modulation of the hierarchy of expression of quinpirole-enhanced hyperactivity via a non-associative process.