Parental methadone treatment: a multigenerational study of development and behavior in offspring

After 60 days of treating both sexes with daily oral doses of 15 mg/kg methadone hydrochloride, Wistar rats were mated. Drug treatment of females continued until the weaning of their pups. The body weight of pups was reduced compared to controls up to weaning, and viability was significantly decreased. Ontogeny of reflexes was delayed, and exploration in an open-field arena was reduced up to 2 weeks of age, but then increased above controls. Defecation in the open-field arena was lessened. When only the sire received methadone, only the increase in exploratory behavior and the decrease in defecation occurred. Breeding offspring (F1) of which both parents had methadone treatment gave F2 generation offspring for which neonatal mortality was significantly elevated and defecation in the open-field arena was lessened at 21 days. No changes clearly traceable to methadone were found in the subsequent F3 generation. Some F3 generation rats were treated with methadone and bred in the same manner as the original parental generation. The resulting pups, having the genealogy twice-exposed to methadone, were not significantly different from those whose immediate parents only received the drug.