Development of tissue damage, inflammation and resolution following stroke: An immunohistochemical and quantitative planimetric study

Abstract

Development and resolution of the lesion produced by occlusion of the middle cerebral artery (MCAO) was studied through quantitative planimetry and histologic/immunohistochemical techniques. MCAO, performed in spontaneously hypertensive rats (SHR), initially (1–3 days) produced large, consistent cerebral cortical infarctions and an increase in ipsilateral hemispheric size (i.e., swelling) quantitated by planimetry on 2,3,5-triphenyltetrazolium chloride (TTC)-stained gross tissue sections. These initial changes correlated well with changes identified from 2 h to 3 days using hematoxylin and eosin stained histologic tissue sections and immunohistochemical techniques including: the progressive development of a cortical area of pan necrosis, infiltration of neutrophils into infarcted tissues, and activation of astroglia. During the initial 2 days following MCAO, glial fibrillary acidic protein immunoreactive cells increased in number and became larger and more intensely fluorescent medial to the cortical infarct. At 5 to 15 days, both the infarct and the ipsilateral hemisphere decreased in size. These changes correlated with the presence of abundant macrophages, and cavitation of the lesion along its medial border. Also during this period, a loose connective tissue matrix formed along the superficial aspect of the infarct. This connective tissue contained fibroblasts, extracellular matrix immunoreactive for laminin and collagen, capillary buds indicating neovascularization, and abundant macrophages. By the final timepoint (30 days), necrotic tissue could no longer be detected in either gross or histologic tissue sections, the inflammatory infiltrate had resolved, and the connective tissue was removed. This study represents the first detailed description of the cellular/tissue changes following focal ischemia with a correlation of quantitative planimetric and histologic/immunohistochemical information provided throughout the development and resolution of cerebral ischemie damage. Based on these data, a four-stage organizational matrix of cellular/tissue events (i.e., neuronal death, inflammation, organization, and resolution) is presented that defines the evolution of infarction through cerebral healing that occurs in permanent focal stroke.