Adult murine hippocampal neurogenesis is inhibited by sustained IL-1 beta and not rescued by voluntary running

Acute neuroinflammation reduces adult hippocampal neurogenesis but the role of chronic neuroinflammation, which may be more representative of ongoing processes in CNS disorders, remains relatively unknown. Interleukin-1 beta (IL-1 beta) is a pro-inflammatory cytokine that has been shown to acutely impair neurogenesis. To further investigate the relationship between sustained 1L-1 beta expression and adult neurogenesis, a mouse model with an IL-1 beta excisionally activated transgene, IL-1 beta(XAT) was utilized. Upon exposure to Cre recombinase, IL-1 beta overexpression in this model results in chronic neuroinflammation, which persists up to 12 months and causes glial activation, cellular recruitment, and deficits in learning and memory. We hypothesized that adult neurogenesis would be reduced by sustained hippocampal IL-1 beta overexpression and rescued by voluntary running, which has been shown to enhance neurogenesis. Hippocampal inflammation in the IL-1 beta(XAT) model severely impaired doublecortin (DCX) positive cells at 1 and 3 months after IL-1 beta induction. Furthermore, BrdU labeling demonstrated a shift in cell lineage from neuronal to astroglial in the context of sustained hippocampal IL-1 beta overexpression. Deletion of the IL-1 receptor prevented the decrease in DCX+ cells. Voluntary running did not attenuate the effects of IL-1 beta expression demonstrated by DCX staining. These results suggest that chronic neuroinflammation severely impairs adult hippocampal neurogenesis and voluntary running is not beneficial as a therapy to rescue these effects. (C) 2011 Elsevier Inc. All rights reserved