Does route of methamphetamine exposure during pregnancy have an impact on neonatal development and behaviour in rat offspring?

Many preclinical studies have aimed to elucidate the effects of methamphetamine (MA) exposure during pregnancy on the offspring in recent years. However, the severity of effects on the neonate may be related to the subcutaneous (sc) route of administration of the drug that is often employed (88% of preclinical studies) and consequently the delivered dose that the foetus is exposed to. To date there is a paucity of comparative studies investigating different routes of administration for MA during pregnancy and it is not known how these different routes compare when it comes to neonatal outcome. Thus, the aim of this study was to determine if the route of administration of MA (oral gavage or sc injection) during pregnancy at a pharmacological dose affects the magnitude of neurodevelopmental and behavioural effects in the resultant rat offspring. Pregnant Sprague-Dawley dams (n=10 dams/group) received MA (3.75 mg/kg) or control (distilled water) via oral gavage or sc injection from gestation day 7-21. A range of well-recognised neurodevelopmental parameters were examined in the offspring. When administered sc, MA significantly reduced maternal weight gain and altered maternal behaviour; mothers spent less time in the nest with pups and spent less time nursing compared to controls. Significant impairments in neurodevelopmental parameters were evident in both MA treatment groups. Somatic development such as pinna unfolding, fur appearance and eye opening were all delayed after MA exposure but these impairments were more pronounced in the MA sc group. Other somatic parameters such as ano-genital distance and body length were only impeded by sc MA. Behavioural development in the surface righting, inclined plane and forelimb grip tests were also altered for both MA treatment groups. This study demonstrates that prenatal MA can have a profound effect on neonatal outcome, but this can be exacerbated if given via the subcutaneous route, as well as producing additional effects not seen with the oral gavage route. Consequently, the route of administration should be considered when interpreting preclinical studies investigating prenatal MA exposure.