Mechanisms of neurodegeneration after severe hypoxic-ischemic injury in the neonatal rat brain.
OBJECTIVE
Apoptosis is implicated in mild-moderate ischemic injury. Cell death pathways in the severely ischemic brain are not characterized. We sought to determine the role of apoptosis in the severely ischemic immature brain.


METHODS
Seven-day old rats were randomly assigned to mild-moderate or severe cerebral hypoxia-ischemia (HI) group. After ligating the right common carotid artery, animals were subjected to hypoxia for 90min in the mild-moderate HI or 180min in the severe HI. The core and peri-infarct area were measured in H&E stained brain sections using NIS Elements software. Brain sections were processed for caspase-3, AIF and RIP3 immuno-staining. Number of positive cells were counted and compared between the two groups.


RESULTS
The core constituted a significantly higher proportion of the ischemic lesion in the severely compared to the moderately injured brain (P<0.04) up to 7 days post-injury. Apoptotic cell death was significantly higher (P<0.05) in the core than the peri-infarct of the severe HI brain. In the peri-infarct area of severe HI, AIF-induced cell death increased over time and caspase-3 and AIF equally mediated neuronal death. Necroptosis was significantly higher (P=0.02) in the peri-infarct of the severe HI lesion compared to the moderate HI lesion. In males, but not in females, apoptosis was higher in moderate compared to severe HI.


CONCLUSIONS
Caspase-independent cell death plays an important role in severe ischemic injury. Injury severity, timing of intervention post-injury and sex of the animal are important determinants in designing neuroprotective intervention for the severely ischemic immature brain.
Neuroscience and Mental Health Program, Hospital for Sick Children Research Institute, University of Toronto, Toronto, ON, Canada. Electronic address: r.askalan@utoronto.ca.
Rand
R
Askalan
Neuroscience and Mental Health Program, Hospital for Sick Children Research Institute, University of Toronto, Toronto, ON, Canada.
Nadia
N
Gabarin
Section of Pediatric Neurosciences, Stollery Children׳s Hospital, University of Alberta, Edmonton, AB, Canada.
Edward A
EA
Armstrong
Neuroscience and Mental Health Program, Hospital for Sick Children Research Institute, University of Toronto, Toronto, ON, Canada.
Yuan
Y
Fang Liu
Neuroscience and Mental Health Program, Hospital for Sick Children Research Institute, University of Toronto, Toronto, ON, Canada.
Deema
D
Couchman
Section of Pediatric Neurosciences, Stollery Children׳s Hospital, University of Alberta, Edmonton, AB, Canada.
Jerome Y
JY
Yager
D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000378:metabolism* / Q000473:pathology*; D005260:Female; D020925:Hypoxia-Ischemia, Brain / Q000378:metabolism* / Q000473:pathology*; D008297:Male; D019636:Neurodegenerative Diseases / Q000378:metabolism* / Q000473:pathology*; D051381:Rats; D012720:Severity of Illness Index
Apoptosis; Neonatal brain; Neuroprotection; Severe ischemia