Effects of prenatal nicotine exposure on biochemical development of rat brain regions: maternal drug infusions via osmotic minipumps.

The effects of a continuous 16-day gestational exposure to nicotine on brain development were examined in the offspring of dams who received a minipump implant on the 4th day of gestation. Maternal viability was unaffected and weight gain was only reduced slightly, but nearly half the dams failed to give birth; dams delivering pups had normal litter sizes. Examination of fetal macromolecules on the 18th day of gestation revealed specific deficits in cell number (DNA) in developing brain tissue as opposed to the rest of the fetus, accompanied by parallel shortfalls in other macromolecules (RNA, protein). After birth, brain development in the nicotine-exposed animals showed persistent abnormalities in the timing of maturational events, with elevated levels of ornithine decarboxylase (an enzymatic marker related to cellular maturation) detectable in all brain regions. Subsequent effects on macromolecules were highly selective regionally, with clear distinctions between areas in which neuronal replication occurs relatively late (cerebellum) compared to early-developing regions (midbrain plus brainstem). Differences apparent between the effects of infused maternal nicotine and those noted previously in studies with nicotine injections indicate that the drug does exert primary effects on developing neural tissues, but that other factors associated with the injection route (such as hypoxia and ischemia consequent to acute effects of nicotine) can interact with the drug to influence brain cell maturation.