Diminished DG volume has implications for learning and memory during development. Just as importantly, the DG is one of the few brain regions in which neurogenesis occurs throughout adulthood (Ming and Song, 2005). Thus, delay of development in DG volume, and/or loss of DG volume during Gefitinib molecular weight development, would be expected to impact the acquisition of early neurocognitive functions, while also impairing brain resilience in later life. Further studies are needed to examine effects on the aging brain of early chronic exposure to Pb. The findings suggested neuroimmune system disruption, but not chronic neuroinflammation and heightened microglial activation. Furthermore, microglial mean cell body volume differences

in animals with lowest vs. higher Pb chronic exposure suggested qualitatively different types of neuroimmune disruption in these groups. Further studies of cytokine levels, find more in combination with cytokine gene expression, could be useful for confirming these findings. Studies are needed to examine the independent effects on microglia of local Pb concentrations and increased δ-ALA, at lowest and higher chronic and acute doses, and using additional microglial activation markers such as CD45, CD68, and F4/80. Investigating concentrations of Pb in brain and increased brain δ-ALA as distinct neurotoxic triggers may help differentiate their roles in effect pathways. It is also important to examine the

effects of early chronic lowest and higher levels of Pb concentrations on progenitor cells. We selected DG as the target structure in these studies because of its critical role in learning and memory, and its role in neurogenesis during adulthood. Additional studies are needed to test for evidence of neuroimmune disruption in other brain regions implicated by results from the child and animal lead exposure literature, including for example, caudate putamen and substantia nigra. Mice chronically exposed to Pb from birth

to PND 28, with blood Pb levels from 2.48 to 20.31 μg/dL, had dose-dependent reduction of IL6 gene expression in posterior and anterior brain, significantly less IL6 in posterior brain, dose-dependent reduction in DG microglia mean cell body number, and reduced DG volume. Chronic Pb exposure Thiamine-diphosphate kinase promoted microglia with broad variability in mean cell body volume, only in animals with blood levels between 2.48 μg/dL and 4.65 μg/dL, and with no increases in inflammatory markers. The findings lend initial support for neuroimmune system disruption, but not neuroinflammation, as one source of abnormal brain development with chronic developmental exposure to Pb. The authors declare that there are no conflicts of interest. The authors would like to acknowledge Mari Golub, Environmental Toxicology, UC Davis, for her assistance in the preparation of the final manuscript. The authors would also like to acknowledge Benjamin Valencia for his assistance in the completion of the animal procedures.