Effect of prenatal and postnatal methamphetamine exposure on nociception in adult female rats.

The aim of the present study was to determine effects of methamphetamine (MA) exposure and cross-fostering on thermal nociceptive thresholds in different estrous phases in adult female rats. Rat mothers were exposed daily to injection of MA (5 mg/kg) or saline for 9 weeks: prior to impregnation, throughout gestation and lactation periods. Dams without any injections were used as an absolute control. On postnatal day 1, pups were cross-fostered so that each mother raised four pups of her own and eight pups from the mothers with the other two treatments. Offspring females were tested in adulthood (85-90 days) for thermal nociception as latency [s] of withdrawal reaction of forelimbs, hind limbs, and tail. Our results showed that prenatal MA exposure did not affect the nociception in adulthood, while postnatal MA exposure (i.e., MA administration to lactating mothers) had pro-nociceptive effects. The effect of postnatal MA exposure was apparent in both, fore- and hind limbs, while the latency to tail withdrawal reaction was the same among the groups. In addition, the pro-nociceptive effect of postnatal MA exposure did not depend on estrous cycle. This study indicates that postnatal but not prenatal exposure to MA affects nociception in adult female rats. However, it is still not clear whether the pro-nociceptive effect of postnatal MA exposure is linked to direct action of MA on neuronal organization, or to indirect action of MA mediated by impaired maternal care.