Stroke in the neonatal brain is an important cause of neurologic morbidity. To characterize the dynamics of neural progenitor cell proliferation and maturation after survival delays in the neonatal brain following ischemia, we utilized unilateral carotid ligation alone to produce infarcts in postnatal day 12 CD1 mice. We investigated the neurogenesis derived from the sub-ventricular zone and the sub-granular zone of the dentate gyrus subsequent to injury. Newly produced cells were labeled by bromodeoxyuridine at ~1week (P18-20) after the insult by 5 I.P. injections (each 50mg/kg). Subsequent migration and differentiation of the newborn cells was investigated at postnatal day 40 by immunohistochemistry for molecular neuronal and glial cell-lineage markers and BrdU incorporation. Cresyl violet stain demonstrated massive loss of neurons in the ipsilateral septal hippocampus in the CA3 and CA1 regions associated with atrophy. Total counts of new cells were significantly lowered not only in the ipsilateral injured but also the contralateral uninjured hippocampi and correlated with the lesion induced atrophy. Bilateral percent neuronal commitments in the dentate gyri however, were not significantly different from control. New cell densities in the neocortex and striatum increased bilaterally after neonatal stroke. The predominantly non-neuronal commitment of the SVZ derived new cells was similar to the percentage of non-neuronal commitment in controls. In conclusion, neurogenesis occurring at 1 week after neonatal ischemia in the model maintained cell-lineage commitment patterns similar to sham controls. However, the total number of hippocampal SGZ-derived new neurons was reduced bilaterally; in contrast, the SVZ-derived neurogenesis was amplified.

Stroke in term neonates remains a significant cause of long-term neurological morbidity. This study was designed to assess the relationships between ischemic stroke induced by permanent unilateral carotid ligation in P12 CD1 mice and the structural and functional outcomes in the young mice as a consequence.After P12 ischemic strokes, mice were behaviorally tested using accelerated rotorod, spontaneous alternation on a T-maze, open-field, and cylinder tests between P33 and P39. Brain injury was scored by histology at P40 with cresyl violet-stained coronal sections and computerized quantification of the ischemic injury.The ligation-injured mice were not different from controls on cylinder testing for asymmetric use of their forelimb, or on rotorod measures. In the spontaneous alternation task, however, injured mice demonstrated significantly lower rates of alternation indicating a deficit in working memory. Openfield testing repeated on two consecutive days revealed that the ligated mice were less active than the controls and that they failed to habituate to the open field environment between sessions indicating a learning deficit. Overall, our results demonstrate that ischemia induced by our neonatal stroke model produces behavioral deficits that are consistent with the brain injury.

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Stroke is a major cause of neurologic morbidity in neonates and children. Because neonatal and pediatric stroke frequently present with seizures, the question of which anticonvulsant best blocks acute ischemic seizures and reduces injury is clinically relevant. The purpose of this study was to determine the extent to which gabapentin is neuroprotective and suppresses acute seizures in this model of ischemic injury in the immature brain. Postnatal day 12 CD1 mice underwent right common carotid artery ligation and immediately after ligation received a 0, 50, 100, 150, or 200 mg/kg dose of gabapentin intraperitoneally. Acute seizure activity was behaviorally scored and hemispheric brain atrophy measured. In vehicle-treated mice, severity of acute seizures correlated with hemispheric brain atrophy 4 wks later. Gabapentin significantly decreased acute seizures at 200 mg/kg and reduced brain atrophy at doses of 150 and 200 mg/kg but not at lower doses. These results suggest that gabapentin effectively reduces acute seizures and injury after ischemia in the immature brain. When analyzed by animal sex, the data suggest that gabapentin may more effectively reduce acute seizures and injury in male pups vs. female pups. (Pediatr Res 64: 81-85, 2008)

Background and Purpose— Notch receptors (1–4) are membrane proteins that, on ligand stilumation, release their cytoplasmic domains to serve as transcription factors. Notch-2 promotes proliferation both during development and cancer, but its role in response to ischemic injury is less well understood. The purpose of this study was to understand whether Notch-2 is induced after neonatal stroke and to investigate its functional relevance. Methods— P12 CD1 mice were subjected to permanent unilateral (right-sided) double ligation of the common carotid artery. Results— Neonatal ischemia induces a progressive brain injury with prolonged apoptosis and Notch-2 up-regulation. Notch-2 expression was induced shortly after injury in hippocampal areas with elevated c-fos activation and increased cell death. Long-term induction of Notch-2 also occurred in CA1 and CA3 in and around areas of cell death, and had a distinct pattern of expression as compared to Notch-1. In vitro oxygen glucose deprivation treatment showed a similar increase in Notch-2 in apoptotic cells. In vitro gain of function experiments, using an active form of Notch-2, show that Notch-2 induction is neurotoxic to a comparable extent as oxygen glucose deprivation treatment. Conclusions— These results suggest that Notch-2 up-regulation after neonatal ischemia is detrimental to neuronal survival.