Effects of dose and interdose interval on locomotor sensitization to the dopamine agonist quinpirole.

To assess whether the interval between injections affects the course of locomotor sensitization to quinpirole, groups of rats were injected every 2, 4, or 8 days with quinpirole (0, 0.025, 0.25, 0.5, and 2.5 mg/kg; n = 222) and their locomotor activity monitored after each injection for a total of 10 tests. Results indicate that the number of drug injections, rather than the interval between them, predominantly controls the development of locomotor sensitization to quinpirole. It is suggested that this may reflect a rapid induction but slow decay time for a response-enhancing factor stimulated by each injection of quinpirole, and that the effects of this putative factor are cumulative but saturable.