Neuronal and Glial Alterations Due to Focal Cortical Hypoxia Induced by Direct Cobalt Chloride (CoCl₂) Brain Injection

Abstract

Ischemic brain injury is a dynamic process that involves oxidative stress, inflammation, and cell death, as well as activation of endogenous adaptive and regenerative mechanisms depending on activation of transcription factors such as hypoxia inducible factor 1-alpha (HIF-1α). Because CoCl₂ activates HIF-1α, we described a new focal-hypoxia model by direct intracerebral CoCl₂ injection. Adult male Wistar rats were intracerebrally injected with CoCl₂ (2 μl–50 mM), in frontoparietal cortex of right hemisphere, and saline (2 μl) in the contralateral hemisphere. In slides of fixed brains at 1, 6, 9, 24 h or 5 day after treatment, TTC, histochemistry (toluidine blue, Hoescht-33342, TUNEL), immunostaining (HIF-1α, GFAP), Lycopersicon esculentum lectin staining, and electron microscopy (EM) were performed. Immediately after 1 h post CoCl₂ injection, HIF-1α stabilization and neuronal nuclear shrinkage and cromathin condensation were observed by immunostaining and EM, respectively. Neuronal apoptotic nuclear morphology and GFAP immunoreactivity and lectin maximal reactivity were detected during 6–9 h. Ultrastructural alterations of morphology included edematous perinuclear cytoplasm, organelles and endoplasmic reticulum (RE) enlargement, mitochondrial swelling with increased matrix density, and deposits of electron-dense material. Neurons showed particular nuclear indentations. Astrocytes and oligodendrocytes presented alterations in both nuclei and RE with dilated lumen and altered mitochondrias, and all these ultrastructural changes became detectable at day 5. CoCl₂ cortical injection mimics focal brain ischemia, inducing neuronal death and glial activation. This model brings the opportunity to develop focal ischemia in selected brain areas to study their functional consequences and potential pharmacological therapies for in vivo models of stroke.