Neurodegeneration, Myelin Loss and Glial Response in the Three-Vessel Global Ischemia Model in Rat.

Tatiana Anan’Ina,Konstantin Usov,Marina Kudabaeva,Mark Plotnikov,Alena Kisel,Vera Smolyakova,Elena Krutenkova,Marina Khodanovich,Galina Chernysheva

doi:10.3390/ijms21176246

Abstract

(1) Background: Although myelin disruption is an integral part of ischemic brain injury, it is rarely the subject of research, particularly in animal models. This study assessed for the first time, myelin and oligodendrocyte loss in a three-vessel model of global cerebral ischemia (GCI), which causes hippocampal damage. In addition, we investigated the relationships between demyelination and changes in microglia and astrocytes, as well as oligodendrogenesis in the hippocampus; (2) Methods: Adult male Wistar rats (n = 15) underwent complete interruption of cerebral blood flow for 7 min by ligation of the major arteries supplying the brain or sham-operation. At 10 and 30 days after the surgery, brain slices were stained for neurodegeneration with Fluoro-Jade C and immunohistochemically to assess myelin content (MBP+ percentage of total area), oligodendrocyte (CNP+ cells) and neuronal (NeuN+ cells) loss, neuroinflammation (Iba1+ cells), astrogliosis (GFAP+ cells) and oligodendrogenesis (NG2+ cells); (3) Results: 10 days after GCI significant myelin and oligodendrocyte loss was found only in the stratum oriens and stratum pyramidale. By the 30th day, demyelination in these hippocampal layers intensified and affected the substratum radiatum. In addition to myelin damage, activation and an increase in the number of microglia and astrocytes in the corresponding layers, a loss of the CA1 pyramidal neurons, and neurodegeneration in the neocortex and thalamus was observed. At a 10-day time point, we observed rod-shaped microglia in the substratum radiatum. Parallel with ongoing myelin loss on the 30th day after ischemia, we found significant oligodendrogenesis in demyelinated hippocampal layers; (4) Conclusions: Our study showed that GCI-simulating cardiac arrest in humans—causes not only the loss of pyramidal neurons in the CA1 field, but also the myelin loss of adjacent layers of the hippocampus.

Highlights

White-matter injury—along with neuronal loss—is an integral part of the pathologic processes that accompany cerebrovascular diseases
We investigated the dynamics of neuronal loss, neurodegeneration, astrogliosis, inflammation, utilization of disrupted myelin by microglia/macrophages and specific rod-shaped changes of microglial morphology
Our results show that myelin and oligodendrocyte loss was observed 10 days after global cerebral ischemia (GCI) and intensified by the 30th day in the hippocampal layers adjacent to the pyramidal neurons in the CA1 field (SO and stratum radiatum (SR)), as well as the stratum pyramidale (SP) layer itself

Summary

Introduction

White-matter injury—along with neuronal loss—is an integral part of the pathologic processes that accompany cerebrovascular diseases. Poor white-matter recovery significantly affects the long-term outcome after an acute stroke [1], impairs sensorimotor function and causes profound neurobehavioral and cognitive impairment [2]. Despite its importance for normal brain functioning and recovery after stroke, demyelination has rarely been investigated in the animal models of brain ischemia. The studies on the animal middle cerebral artery occlusion (MCAO) model [4,5,6,7,8] studies showed that myelin destruction begins from the first day and even as early as hours after stroke. The mechanisms of demyelination [5,6,8] include intramyelinic edema that manifests as myelin pallor, further vacuole formation and sheath destruction followed by myelin debris clearance by microglia and macrophages. Molecular mechanisms underlying oligodendrocyte death include glutamate excitotoxicity, mitochondrial dysfunction, oxidative stress and proinflammatory factors [10]

Methods

Results

Conclusion