Monitoring ischemic cerebral injury in spontaneously hypertensive rats by diffusion tensor imaging

Abstract

AIM:We have applied diffusion tensor imaging (DTI) to interrogate microstructural changes in white matter integrity in a widely used middle cerebral artery occlusion (MCAO) model of cerebral ischemia. MATERIAL and METHODS:We performed ex vivo DTI 35 days after 60 minutes transient focal ischemia in male spontaneously hypertensive rats and generated fractional anisotropy (FA), mean, axial and radial diffusivity maps. Regions of interest corresponding to external capsule (EC), corpus callosum (CC) and internal capsule (IC) were compared among sham and stroked rats. We compared tractographic projections of white matter fiber patterns and examined white matter integrity by Luxol fast blue histological analysis. We also determined infarct lesion volumes at 24 hours post-ischemia by T2-weighted magnetic resonance imaging (MRI) or at 35 days by histological staining with cresyl violet. RESULTS:We found alterations in EC and IC, but not CC, as represented by decreased FA and increased mean, axial and radial diffusivities. The size of the ischemic lesion detected subacutely by T2-weighted MRI or at 35 days by histological staining correlated with the decline in FA in the affected structures. Tractography revealed disruption of fiber trajectories through the EC and reorientation of fibers within the caudate/putamen of rats subjected to MCAO. Similarly, loss of white matter integrity in the EC and increased white matter density in the caudate/putamen along the infarct border zone was evidenced by Luxol fast blue staining. CONCLUSION:Diffusion tensor imaging therefore allows for monitoring of white matter injury and reorganization in hypertensive rats.

Effects of Xiaoshuan Enteric-Coated Capsule on White and Gray Matter Injury Evaluated by Diffusion Tensor Imaging in Ischemic Stroke

“…After the administration of XSECC, the FA value in the corpus callosum, internal capsule and external capsule increased notably after stroke. The increased FA might arise from an increased number of aligned fibers or greater myelination 40,45 . Additionally, the increased FA was linked with the decreased λ // , λ ⊥ and ADC on the 3rd day and reduced ADC on the 30th day in the external capsule, indicating that drug treatment could reduce the damage of white matter axon and myelin, and maintain the integrity of the white matter structure and function.…”

“…ADC is the diffusion rate of water molecules 39 , and a reduced ADC value means increased limits in tissue. λ // is the diffusion rate that parallels the axons and is mostly used to reflect the integrity of the axons 40 . In early ischemia, λ // will be significantly reduced due to severe cell edema and axonal damage 40 ; With ischemic time prolonging, λ // will increase due to the gradually aggravated vasogenic edema and the loss of nerve fiber 40,41 .…”

“…λ // is the diffusion rate that parallels the axons and is mostly used to reflect the integrity of the axons 40 . In early ischemia, λ // will be significantly reduced due to severe cell edema and axonal damage 40 ; With ischemic time prolonging, λ // will increase due to the gradually aggravated vasogenic edema and the loss of nerve fiber 40,41 . λ ⊥ is the diffusion rate perpendicular to the axons and the change of λ ⊥ can reflect the pathological changes of demyelination 16,39,42 .…”