Delay in postnatal growth and development of offspring produced by maternal restraint stress during pregnancy in the rat

Rats were subjected to restraint stress for nine hours daily, on three consecutive days, at various stages of pregnancy from days 9–20, and the postnatal development and behaviour of the offspring assessed on a wide‐ranging battery of tests. Stress at any of the stages of pregnancy investigated caused a significant decrease in offspring body weight persisting up to 6 weeks of age, and delayed the appearance of certain developmental landmarks such as ear opening, auditory startle and cliff avoidance responses. Postnatal mortality and impairment of ability to orient to the home cage were also significantly increased in the offspring from rats stressed on days 18–20 of pregnancy. In a second experiment, the effects of restraint stress on days 18–20 were investigated in more detail. At birth, stressed and control offspring were fostered onto mothers from the same treatment group or cross‐fostered onto mothers from the opposite treatment group and assessed as before, to determine whether the adverse effects observed in the first experiment were prenatally or postnatally mediated. The effects were most marked in prenatally stressed pups reared by stressed mothers and least marked in controls reared by controls, with the other two cross‐fostered groups being intermediate; this indicates that the effects were induced partly prenatally at the time of treatment and partly postnatally by the rearing mothers that had been stressed.