Progeny of male rats treated with methadone: physiological and behavioural effects

Male rats were injected with methadone HCl (METH) at 5 mg/kg s.c. for 4 days prior to mating with drug-free females. Offspring resulting from these matings were compared with offspring of drug-free males. The progeny of METH-treated males gained less weight after weaning and had lighter thymuses as adults (but not in infancy). Gonadal weights did not differ in infancy or adulthood, and adrenal weights were heavier in female offspring in adulthood. In adulthood METH offspring were significantly different from controls on all behavioural tests used (open field activity, activity cage activity, passive avoidance latencies, shuttle box avoidances, and rotarod latencies), with the differences frequently affected by test order, days of testing, or sex of offspring. The effects in progeny of METH-treated males in the absence of differences in litter size or neonatal mortality indicate that paternal drug ingestion prior to mating can produce physiological and behavioural changes in progeny that are not dependent on detectable effects on early viability or growth.