Spreading depression and selective neuronal death

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Our research results are divided into three parts ; 1) MAP2 depletion in the hippocampus following spreading depression 2) SNAP-25 expression after repeated induction of spreading depression 3) glutamate release during spreading depression1) MAP2 depletion in the hippocampus following spreading depressionTraumatic brain injury induces neuronal cell loss in area CA3 of the hippocampus. However, it has not yet been established why trauma of the cortex induces neuroral damage in a remote area. Spreading depression (SD) may be one potential mechanism for this pathophysiology. The present study evaluated whether SD on the cortex evokes a pathological change in the hippocampus. Forty-two Fisher rats were assigned to four groups : Group I : sham operation (n=7), Group II : right carotid occlusion (UO) for 7days. (n=7), GroupIII : repeated induction of SD by KCl application on dura for 7 days (n=7), GroupIII'for 3hours (n=7), Group IV : SD induction and UO for seven days (n=14) GroupIV' for 3h … More ours (n=7) In five out of 7 animals in GroupsIII' and IV', cerebral blood flow was monitored using laser Doppler flowmetry for 3h during the passage of SD.The brains were pocessed for immunohistochemical analysis of microtubule-associated protein 2 (MAP2). Reactive hyperemia induced by SD was not significantly suppressed by right carotid occlusion (194(]SY+-[))25% and 181(]SY+-[))42% UO in Groups III and IV,respectively). In six out of seven animals in 7 days model of Group IV,and three animals in 7 days model of Group III,MAP2 depletion in the CA3 area of the hippocampus (partly including CA2) was observed, although no change in the hippocampus was observed in other groups. In conclution, SD in combination with UO yielded reproducible lesions in CA3. Neuronal injury in the hippocampus after brain trauma may be attributable to SD in combination with the blood flow restriction.2) SNAP-25 expression after repeated induction of spreading depressionRepeated induction of cortical spreading depression (SD) elicits neuronal cell loss in area CA3 of the hippocampus, when the blood flow is restricted by unilateral carotid occlusion. This model may be able to extrapolated to remote neuronal injury due to traumatic brain injury. In this study, we evaluated whether cortical SD augmented hippocampal glutamate release by immunohistochemical analysis of SNAP-25, an exocytosis-related protein. Fifteen rats were assigned to three groups of five : I ; control ; II ; SD induction and unilateral carotid artery occlusion (UO) for 3h ; III ; SD and UO for seven days. The brains were processed for immunohistochemical analysis of SNAP-25 and MAP2. Two of the five animals in Group II showed MAP2 depletion in the CA3 area of the hippocampus (including partly of CA2), was observed, whereas hippocampal changes were observed in Group I.Fairly strong SNAP-25 immunoreactivity present, in the area corresponding to the MAP2 depleted region in Group II.Four of the five Group III animals showed MAP2 depletion in CA-3 of the hippocampus, but, no distinct SNAP-25 immunostaining was observed, not even in the MAP2 depletion area. In conclusion, glutamate release in CA-3 may be augmented by cortically induced SD on the cortex for three hours. Remote neuronal injury in the hippocampus resulting from cortically induced SD may be modulated by glutamate release.3) glutamate release during spreading depressionSpreading depression (SD) seems to play a key role in extending neuronal damage in the penumbra. SD alone does not elicit neuronal damage, so supplemental factors which might turn SD into a harmful stimulus were examined. Eleven male Fischer rats were anesthetized and mechanically ventilated in a stereotaxic frame. A laser Doppler flowmeter, an electroenzymatic electrode for measuring glutamate and a calomel electrode for measuring DC potential were placed through a cranial window positioned 3 mm away from a second window where KCl soaked cotton was placed to initiate SD.The left carotid artery was ligated to suppress reactive hyperemia of SD.The electroenzymatic electrode continuously monitored extracellular glutamate which was oxidized by L-glutamate oxidase perfused through the electrode. Glutamate levels increased immediately on initiation of SD from 34(]SY+-[)24 mM/L to 48(]SY+-[)47 mM/L (p<0.05) before carotid occlusion, from 41(]SY+-[)25 mM/L to 53(]SY+-[)41 mM/L (p<0.05) after ligation of the carotid artery, returned to the control value when the DC potential recovered. There was no positive correlation between the duration of SD and suppression of reactive hyperemia, however, a positive correlation (p<0.05) was found between the duration of SD and the glutamate concentration. In conclusion, high extracellular glutamate levels accompany prolonged SD.Prolonged SD in ischemic penumbra may be caused by high extracelluar glutamate. Less