Consistent Injury to Medium Spiny Neurons and White Matter in the Mouse Striatum after Prolonged Transient Global Cerebral Ischemia

Abstract

A reproducible transient global cerebral ischemia (tGCI) mouse model has not been fully established. Although striatal neurons and white matter are recognized to be vulnerable to ischemia, their injury after tGCI in mice has not been elucidated. The purpose of this study was to evaluate injuries to striatal neurons and white matter after tGCI in C57BL/6 mice, and to develop a reproducible tGCI model. Male C57BL/6 mice were subjected to tGCI by bilateral common carotid artery occlusion (BCCAO). Mice whose cortical cerebral blood flow after BCCAO decreased to less than 13% of the pre-ischemic value were used. Histological analysis showed that at 3 days after 22 min of BCCAO, striatal neurons were injured more consistently than those in other brain regions. Quantitative analysis of cytochrome c release into the cytosol and DNA fragmentation in the striatum showed consistent injury to the striatum. Immunohistochemistry and Western blot analysis revealed that DARPP-32-positive medium spiny neurons, the majority of striatal neurons, were the most vulnerable among the striatal neuronal subpopulations. The striatum (especially medium spiny neurons) was susceptible to oxidative stress after tGCI, which is probably one of the mechanisms of vulnerability. SMI-32 immunostaining showed that white matter in the striatum was also consistently injured 3 days after 22 min of BCCAO. We thus suggest that this is a tGCI model using C57BL/6 mice that consistently produces neuronal and white matter injury in the striatum by a simple technique. This model can be highly applicable for elucidating molecular mechanisms in the brain after global ischemia.

Consistent delayed unilateral neuronal death after modified transient focal cerebral ischemia in mice that mimics neuronal injury after transient global cerebral ischemia

“…The survival rate of the 15-minute PCA-ischemic mice that showed CA1 neuronal death was 95.8%, and all mice that survived 1 day after PCA ischemia survived 7 days after PCA ischemia (longer survival times were not examined). In contrast, the survival rates in previous BCCAO models were low (75% after a 15-minute BCCAO in CD1 mice 29 and 81.6% after a 22-minute BCCAO in C57BL/6 mice (however, more than 50% of the surviving mice suffered from severe akinesia 28 ). Even with the strict criteria for rCBF, only ≤ 50% of the mice were found to have bilateral CA1 injury.…”

“…These histological changes resembled conventional global cerebral ischemia in mice. 13,20,25,27,28 Many researchers have attempted to produce a mouse model of global cerebral ischemia to ensure consistent CA1 injury. The simplest and most widely used model is the bilateral CCA occlusion (BCCAO) model.…”

“…11,13,26,29 The exclusion of animals possessing the PCoA was advantageous in increasing the reproducibility of CA1 neuronal death by the BCCAO method. 11,13,28,29 However, difficulties remain in attaining uniform injury to the CA1 region while retaining high survival and success rates. Another approach that has been used is to decrease CBF by a combination of BCCAO and a reduction in blood flow via vertebrobasilar arteries.…”

“…Because the predominant species for studying genetic mutations is the mouse, a representative mouse model of tGCI is of particular importance. Although mouse tGCI models that produce hippocampal CA1 injury have been established over the past 20 years, 6,13,14,16,20,[25][26][27][28][29] complicated procedures or a high mortality rate may limit their application. Longer ischemic durations or stronger reductions in hippocampal blood flow are needed to ensure consistent injury; however, both of these factors have been associated with high mortality rates.…”

The Role of Parl and HtrA2 in Striatal Neuronal Injury After Transient Global Cerebral Ischemia

“…In an earlier study, we found that ischemic neuronal injury is consistently induced after prolonged transient global ischemia. 24 In addition to ischemic vulnerability, the striatum is reported to be one of the selected areas where severe neuronal loss is observed in PARL knockout and HtrA2 mutant or knockout mice. 11,17,18 Accordingly, the roles of PARL and HtrA2 signaling in the other lesions are obscure.…”