Effects on the postnatal development of the mouse of preconception, postconception and/or suckling exposure to manganese via maternal inhalation exposure to MnO2 dust.

Female mice were exposed either to MnO2 dust (7 hours/day, 5 days/week) or filtered air (control group) for 16 weeks prior to conception. On day 1 of gestation, half of each of these groups was assigned randomly either to MnO2 dust or filtered air exposure until day 17 of gestation. To separate effects of prenatal maternal exposure to MnO2 from postnatal exposure of offspring to Mn via suckling, a complete fostering/-cross-fostering design was employed. Compared to control mothers, mothers exposed to MnO2 prior to conception produced significantly larger litters. Prenatal exposure resulted in reduced neonatal activity scores and retarded offspring growth that persisted into adulthood. Offspring reared by mothers exposed to MnO2 prior to conception and filtered air postconception had significantly lower day 7 postpartum weights compared to offspring reared by mothers exposed to filtered air both prior to and postconception. Also, offspring reared by mothers exposed to MnO2 prior to conception and filtered air postconception had higher day 12 activity scores compared to offspring reared by mothers exposed to filtered air prior to conception and MnO2 postconception. Prenatal exposure to MnO2 depressed neonate activity and continued exposure, via suckling, intensified this depression. Offspring exposed prenatally to MnO2 were retrieved faster than control offspring. Rearing frequency, exploratory behavior, and scores in tests having an activity component were depressed for sexually mature offspring who had been exposed to MnO2 both in utero and via suckling. Independent of in utero exposure history, sexually mature offspring reared by mothers exposed to Mn had significantly reduced cerebellum + brain stem mitochondrial Mn levels. Also, sexually mature offspring of mothers exposed to filtered air that were reared by MnO2 -exposed mothers had lower cerebral mitochondrial Mn levels than offspring of control mothers reared by control foster mothers.