Developmental plasticity in the D1- and D2-mediation of motor behavior in rats depleted of dopamine as neonates.

D1- and D2-like antagonist-induced catalepsy and dorsal immobility were studied in pups (Day 10) and weanlings (Days 20, 28, or 35) that received intraventricular injection of 6-OHDA (50 micrograms/hemisphere) or its vehicle solution or postnatal Day 3. The ability of the D1 of D2 antagonists to induce immobility differed as a function of the lesion condition and the age at the time of testing. Moreover, the two behavioral measures exhibited differences in their specific D1 and D2 receptor modulation. Administration of the D1 antagonist SCH 23390 (0.2 or 1.0 mg/kg) or the D2 antagonist clebopride (1.0, 10.0, or 20.0 mg/kg) led to catalepsy and dorsal immobility in intact rats, regardless of test age. Both antagonists induced catalepsy and dorsal immobility in rats depleted of DA when tested on Day 10. However, the effects of each antagonist in DA-depleted rats were ether negligible or significantly less than in controls when animals were tested as weanlings. These data suggest lesion-induced changes in the DA receptor modulation of motor behavior and that this plasticity requires more than a week to become apparent.