Opiate self-administration in adult offspring of methadone-treated female rats

Chronic treatment of female Sprague-Dawley rats with methadone 5 mg/kg IP throughout gestation and lactation resulted in an increased oral self-administration (S.A.) of morphine by their 85-90-day-old offspring. By day 16 of the S.A. treatment schedule methadone offspring were taking 75 to 80% of their total fluid intake as morphine solution when given a choice between morphine solution and water, while control offspring under the same conditions took 33% of their total fluids as morphine solution. When the subjects were again given a choice between water and morphine solution following a 12-day drug free period, methadone offspring drank a significantly greater percentage of morphine solution than controls. Methadone S.A. in methadone offspring was not different from controls. The reasons for this marked difference between morphine and methadone S.A. are not clear. However, it does appear that chronic maternal exposure to methadone may facilitate development of a morphine-S.A. behavior in their offspring.