Neonatal locomotor and long-term behavioral effects of d-amphetamine in the rat.

Locomotor activity in the neonatal rat was found to increase from birth until the beginning of the 3rd week of life, at which time it peaked and then subsequently declined. Subcutaneous injections of both .25 and 2.0 mg/kg of d-amphetamine increased activity in rats 1-21 days of age, with the maximum effect observed at 4 days of age. No tolerance to d-amphetamine was observed after 6 daily injections beginning at 1, 7, or 14 days of age. The decline in the excitatory effects of the drug thus reflected maturational changes in response to it. Consistent with other observations from this laboratory, no persisting effects of the neonatal drug treatment was observed on adult 2-way avoidance learning.