Differential effects of SCH 23390 on immobility behaviors in developing rats

The effects of a single injection of a dopamine D1 antagonist, SCH 23390, at doses of 0, 0.05, 0.1, and 0.2 mg/kg on three different kinds of immobility behavior were tested in rats of 10, 15, 20, and 30 days of age. Each animal was tested for the dorsal immobility response (DIR), vertical cling catalepsy, and bar catalepsy. A different pattern of results was found for each of the three immobility behaviors. SCH 23390 significantly increased the DIR at each age except 15 days; there was a progressive increase in effect from 10 to 20 to 30 days of age. At the lowest dose, drug-induced bar catalepsy peaked at 15 days of age and declined at 20 and 30 days of age. The effect of SCH 23390 on vertical cling catalepsy increased with age, plateauing at 20 days. Thus, the developmental pattern of immobility responses to this dopamine D1 antagonist differs with each behavior measured.