Does cross-fostering modify the impairing effect of methamphetamine on postnatal development of rat pups?

Our previous studies demonstrated that methamphetamine (MA) administered during gestation and lactation periods impairs maternal behavior as well as the postnatal development of rat pups. The present study tested the hypothesis that the cross-fostering influences the development of rat pups. Mothers were daily exposed to injection of MA (5 mg/kg) and saline for 9 weeks: three weeks prior to impregnation, throughout the entire gestation period and during lactation. As a control (C) females with no injections were used. On postnatal day (PD 1), pups were cross-fostered so that each mother received some of her own and some of the pups of mother with the other treatments. Pup's development and sensorimotor coordination was examined between PD 1 and PD 23. Following tests were used: tail pull (PD 10), righting reflex on surface (PD 12), righting reflex on mid-air (PD 17) and rotarod (PD 23). Our results showed that the birth weight in prenatally MA-exposed pups was lower than controls or saline-exposed pups regardless of sex. Prenatally MA-exposed pups gained less weight than controls or saline-exposed pups regardless of postnatal treatment and sex. Further, our data demonstrated that prenatal and postnatal MA exposure impairs sensorimotor functions. On the other hand, postnatal care of control mothers at least partially suppressed the negative effect of prenatal MA exposure. Our hypothesis, that the cross-fostering may affect postnatal development of pups, was confirmed. Our results support the hypothesis that variation in rat maternal care could serve as a mechanism for a non-genomic behavioral mode of transmission of traits.