Recent studies have shown that neurogenesis in the dentate gyrus of the rod
ent hippocampus continues throughout life. Several physiological and pathol
ogical conditions have been reported to alter the rate of progenitor cell d
ivision resulting in the increased production of mature granule neurons. Ex
citotoxic and mechanical lesions of the granule cell layer also stimulate t
he proliferation of precursor cells suggesting that the death of pre-existi
ng granule neurons may act as a trigger for enhanced neurogenesis. Hippocam
pal pyramidal neurons, and to a lesser extent granule neurons, have been re
ported to die as a result of traumatic brain injury in rodents. To determin
e if the proliferation of precursor cells is enhanced as a result of brain
injury in rodents, newly divided cells were labeled with the thymidine anal
og, bromodeoxyuridine (BrdU), Traumatic brain injury increased the producti
on of BrdU-labeled cells in the dentate gyrus with a maximal rate observed
at 3 days post-injury. These cells, a proportion of which co-localize with
the immature neuronal marker TOAD-64, implanted themselves into the granule
cell layer where they accumulated over time. When examined 1 month post-in
jury, the majority of BrdU-labeled cells co-labeled with the mature neurona
l marker calbindin. These findings show that traumatic brain injury increas
es neurogenesis in the granule cell layer and suggests that these new cells
may contribute to the function of the hippocampus, (C) 2001 Wiley-Liss, In
c.