Morphine treatment during rat pregnancy: neonatal and preweaning consequences.

Abstract

Morphine treatment during pregnancy was scheduled with the view to reproduce physical dependence in female rats and to investigate the occurrence of a neonatal withdrawal syndrome (NWS) as well as more prolonged effects of the narcotic in the preweaned pups. Administration started 5 days prior to mating with the daily dose of 20 mg/kg i.p. injections. All along gestation, the dosage was gradually increased up to the final dose of 56 mg/kg/day on the 16th day when the treatment was interrupted. Pregnant dams showed behavioral manifestations of narcotic dependence and drug abstinence. At birth, morphine-exposed neonates exhibited (1) an approximate 28% decrease in respiratory rates (p less than 0.001) during the first day of life and (2) excessive crying (p less than 0.001) accompanied by restlessness. These two last features are related to clinical signs of the NWS identified in babies born to narcotic-addicted women. A significant delay in the time of eye-opening and an earlier sexual maturation in females only were also found in the postnatally developing morphine offsprings. The NWS and some other developmental changes were considered in relation to the used animal model and to possible processes involved in narcotic interferences with postnatal physical growth and neurobehavioral maturation.