Effects of prenatal immune activation on hippocampal neurogenesis in the rat

Maternal infection during pregnancy has been associated with an increased risk for the development of schizophrenia, a disorder characterized by abnormalities in hippocampal morphology and function. Neurogenesis occurs in the hippocampus throughout development into adulthood and is believed to modulate hippocampal function. This study used a rat model in which bacterial endotoxin, lipopolysaccharide (LPS), is administered to pregnant dams, to test if prenatal immune activation has acute and/or long term effects on various phases of neurogenesis (proliferation, survival, differentiation) in the hippocampal dentate gyrus of offspring. When LPS was administered to dams on gestation days (GD) 15 and 16, there was decreased proliferation of dentate cells at postnatal day (PD) 14 and decreased survival of cells generated at PD14 in offspring. When prenatal exposure to LPS was later in pregnancy (GD 18 and 19), offspring showed decreased survival of cells generated both at the time of LPS exposure and at PD14. There was no change in cell proliferation or survival in adult offspring at PD60, with prenatal LPS exposure. Co-administration of the cyclo-oxygenase inhibitor, ibuprofen (IBU), together with prenatal LPS on GD 15 and 16, was unable to prevent the deficit in neuronal survival at PD14. IBU blocked LPS-induced fever but did not block LPS-induced increases in plasma cytokines and corticosterone in the pregnant dam. This indicates that deficits in neurogenesis caused by prenatal LPS are not mediated by LPS-induced fever or eicosanoid induction, but could be mediated by LPS-induced increases in maternal cytokines or corticosterone.