Abstracts

Rationale: Stroke in the neonatal brain is an important and under-studied cause of neurologic morbidity. Recently we have characterized a new immature mouse model of stroke utilizing unilateral carotid ligation alone to produce infarcts and acute seizures in postnatal day 12 (P12) CD1 mice. We have published the chronic effect of the insult on post-stroke neurogenesis labeled by BrdU 1 week after a P12 insult and quantified after a long survival delay at P40. We found it be negatively modulated both ipsi- and contralaterally in the dentate gyrus with the unilateral injury. Enhanced neural cell proliferation was observed in bilateral sub-ventricular zones. The current study was undertaken to determine the effect of the stroke on neural stem cell proliferation as a function of time. Methods: The temporal dynamics of neural progenitor proliferation in the neonatal brain after ischemia was examined in the sub-ventricular zone (SVZ) and the sub-granular zone (SGZ) of the dentate gyrus 7, 14 and 21 days after ischemia (DAI). Newly dividing cells were confirmed by incorporation of bromodeoxyuridine (BrdU) given as a single IP injection (50mg/kg) 2h before the mouse brains were perfusion fixed at the temporally spaced out time points. To determine the cell types of the newly divided cells, co-labeling with GFAP, Nestin and DCX was ascertained and quantified. Results: The temporal profile of neurogenesis in control CD1 mice showed an age dependant decrease with a ~50% drop in new cell counts at 21DAI compared to 7DAI both in the SVZ and SGZ. We found that neurogenesis was significantly lowered in the ipsilateral injured SGZ of ligated mice, for all the time points investigated, that correlated to both the severity of the stroke injury and acute seizure scores. Neurogenesis in the contralateral SGZ was initially lowered at 7DAI compared to control but by 21DAI was similar to control due to the concomitant age dependant decline noted in controls. Neurogenesis was enhanced in the SVZ of injured brains especially on the ipsilateral side at 7 DAI but returned to control levels at 14 and 21 DAI. Co-labeling with cell type markers showed most cells in the SVZ and SGZ to be Nestin positive at the 2h time point. One-third were positive for GFAP and very few to none co-labeled with DCX. Overall expression of these markers however was consistently higher in the injured brains, ipsilateral more than contralateral both in the SVZ and SGZ. Conclusions: The temporal profile of neural stem cell proliferation was differentially altered in the ipsi- vs. contralateral SGZ after neonatal stroke. The severity of the stroke injury and acute seizures was predictive of the severity of the long-term suppression of ipsilateral SGZ neurogenesis. In the SVZ, the enhanced neurogenesis noted in prior long survival study at P40, temporally peaked at 1 week after the insult and then returned to control levels in this study.