Neuronal and glial regeneration after focal cerebral ischemia in rat, an immunohistochemical and electron microscopical study

Abstract

Objectives: Unilateral middle cerebral artery occlusion (MCAO) is an established rat model for stoke studies. It induces focal cerebral ischemia, prior to necrotic and apoptotic loss of tissue in a circumscribed cortical area, paralleled by temporary motor impairment.

Methods: Here we examined tissue samples from the peri-infarct zone of rats that had survived unilateral MCAO for up to 90 min. With immunohistochemistry we stained sections for proliferation markers Ki 67 and PCNA and for intermediate filament protein nestin. Electron microscopy was employed to assess ultrastructural changes.

Results: All MCAO animals developed pronounced lesions in the motor cortex. Numerous cells in the immediate peri-infarct area and scattered cells which seem to have migrated into the infarcted lesion stained positively for Ki 67 and PCNA. Electron microscopy revealed that cells in the lesion site proliferate along the blood vessels. Most of these cells had the ultrastructural features of fibrillary astrocytes while some of the cells were clearly neurons. Endothelia were in part fenestrated. Some of the surrounding cells showed immunostaining for PCNA, indicating proliferation. Oligodendroglia and myelination could not be seen in the lesion site. Single neuronal contacts exhibited the ultrastructural features of synapses. Reformation of cortical layers could not be observed.

Conclusions: We concluded that in spite of extensive proliferation; neuronal and glial regeneration occurs after MCAO only to a small extent. Revascularization seems to be an important initial step. The observed functional recovery of experimental animals may be due to neuronal plasticity in young rats rather than structural regeneration.

Keywords: Middle cerebral artery occlusion, Rat stroke model, Neuronal regeneration, Revascularization in brain, Electron microscopy, Proliferation markers