The locomotor effects of quinpirole in rats depend on age and gender.

Periadolescence in the rat [postnatal day (PND) 35-50] is an important but understudied period of neurobehavioral development. In this experiment, an ongoing survey of the effects of quinpirole in developing rats was completed by the addition of periadolescent rats to the range of ages tested. PND40 or 50 rats were injected subcutaneously with the dopamine D2/D3 receptor agonist, quinpirole (0.0, 0.02, 0.2, or 2.0 mg/kg), and their locomotor activity was recorded. Periadolescent rats showed adult-like locomotor responses to either the 0.2 or 2.0 mg/kg doses of quinpirole, i.e., the responses were biphasic with respect to time: early suppression of locomotion followed by later activation within a single test session. In younger female rats (PND40) but older male rats (PND50), the lowest dose of quinpirole suppressed activity early in the test session but did not increase it later. In male rats, the magnitude of locomotor activation declined with age. Taken together with previous data from this laboratory, these results suggest that periadolescent rats exhibit locomotor responses that fall along a continuum from a high level of activation just after weaning to a low level of activation in early adulthood.