To study the influence of maternal stress on neonatal locomotor development, rat pups of mothers housed singly and in groups were treated orally with corticosterone from 2 to 15 days of age. Control animals received almond oil vehicle only. The rat pups were subjected to swim-tests
from 8 to 20 days of age to evaluate locomotor development. Swim-test performance demonstrated a retardation of locomotor development in pups treated with corticosterone (P < 0.05). Retardation was most marked in the pups from group-housed mothers and between 13 and 15 days of age.
Comparing pups not treated with hormones, the pups born to group-housed mothers showed significantly (P < 0.05) better performance on swim-testing. The weight gain ofpups from group-housed mothers was significantly (P < 0.05) higher than that of pups from individually caged
mothers. Corticosteroid treatment had no effect on weight gain.