title: Effects of Aging on Hippocampal Neurogenesis After Irradiation.
abstract: OBJECTIVE
  To assess the influence of aging on hippocampal neuronal development after irradiation (IR).
  
  
  METHODS
  Male mice, 2, 4, 6, 12, and 18 months of age, were given a single dose of 0 or 5 Gy of IR. A bromodeoxyuridine (BrdU) incorporation study was used to label newborn cells. Neural progenitors, newborn neurons, and microglia in dentate gyrus (DG) were identified by phenotypic markers, and their numbers were quantified by nonbiased stereology 9 weeks after IR.
  
  
  RESULTS
  BrdU-positive or newborn cells in DG decreased with aging and after IR. The number of neuroblasts and newborn neurons decreased with aging, and a further significant reduction was observed after IR. Total type 1 cells (the putative neural stem cells), and newborn type 1 cells decreased with aging, and further reduction in total type 1 cells was observed after IR. Aging-associated activation of microglia in hippocampus was enhanced after IR.
  
  
  CONCLUSIONS
  The aging-associated decline in hippocampal neurogenesis was further inhibited after IR. Ablation of neural progenitors and activation of microglia may contribute to the inhibition of neuronal development after IR across all ages.
authors.affiliation: Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Zoey
authors.initials: Z
authors.lastname: Cheng
authors.affiliation: Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
authors.forename: Yu-Qing
authors.initials: YQ
authors.lastname: Li
authors.affiliation: Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada; Departments of Radiation Oncology and Medical Biophysics, University of Toronto, Toronto, Ontario, Canada. Electronic address: shun.wong@sunnybrook.ca.
authors.forename: C Shun
authors.initials: CS
authors.lastname: Wong
mesh_terms: D000375:Aging; D000818:Animals; D001973:Bromodeoxyuridine; D016371:Cranial Irradiation; D006624:Hippocampus / Q000166:cytology / Q000502:physiology* / Q000528:radiation effects*; D008297:Male; D051379:Mice; D017628:Microglia / Q000528:radiation effects; D058953:Neural Stem Cells / Q000502:physiology / Q000528:radiation effects*; D055495:Neurogenesis / Q000502:physiology* / Q000528:radiation effects*; D011829:Radiation Dosage
chemical_list: D001973:Bromodeoxyuridine