Enduring consequences of early-life infection on glial and neural cell genesis within cognitive regions of the brain

Systemic infection with Escherichia coli on postnatal day (P) 4 in rats results in significantly altered brain cytokine responses and behavioral changes in adulthood, but only in response to a subsequent immune challenge with lipopolysaccharide [LPS]. The basis for these changes may be long-term changes in glial cell function. We assessed glial and neural cell genesis in the hippocampus, parietal cortex (PAR), and prefrontal cortex (PFC), in neonates just after the infection, as well as in adulthood in response to LPS. E. coli increased the number of newborn microglia within the hippocampus and PAR compared to controls. The total number of microglia was also significantly increased in E. coli-treated pups, with a concomitant decrease in total proliferation. On P33, there were large decreases in numbers of cells coexpressing BrdU and NeuN in all brain regions of E. coli rats compared to controls. In adulthood, basal neurogenesis within the dentate gyrus (DG) did not differ between groups; however, in response to LPS, there was a decrease in neurogenesis in early-infected rats, but an increase in controls to the same challenge. There were also significantly more microglia in the adult DG of early-infected rats, although microglial proliferation in response to LPS was increased in controls. Taken together, we have provided evidence that systemic infection with E. coli early in life has significant, enduring consequences for brain development and subsequent adult function. These changes include marked alterations in glia, as well as influences on neurogenesis in brain regions important for cognition.