CONICET | Buscador de Institutos y Recursos Humanos

Hipoxia is one of the pathological factors inducing neuronal injury. Cobalt Chloride (CoCl2) is a synaptic blocker and pharmacological activator of the hypoxia-inducible factor-1. In order to develop an animal model of focal cerebral hypoxia, adult male Wistar rats were anaesthetized, placed in a stereotaxic device and intracerebrally injected with 2 ul of 50 mM CoCl2. The site of injection, confirmed by histological analysis, was layer 2-3 of right fronto-parietal cortex (Bregma -1.30mm). Five days after the surgery, rats were fixed with 4% W/V paraformaldehyde plus 0.25% v/v glutaraldehyde in 0.1 M phosphate buffer pH 7.4. The cerebral area around the injection site was dissected and postfixed with osmium tetroxide, contrasted with uranil acetate and finally embedded in Durcupan resin. Ultrathin sections were stained with lead citrate, examined in a Zeiss M-9 electron microscope and photographed. The ultraestructural studies showed an inflammatory reaction in the area of injection. Larger intercellular spaces and a disruption of neuronal and glial morphology with thin and extended processes forming an irregular network were observed. In the penumbra zone adjacent to the injection area, the tissue structure was more preserved but we observed abundant images of nuclear cleavage, cytoplasmatic multivesicular contents and altered mitochondrial ultrastructure (abnormal crests with swelling images). Typical synaptic contacts are scarce and there were abnormal presynaptic structures as well as lamellar images of membranous processes and profiles included in the matrix between neurons and glial cells. Outside the penumbra limits, the brain tissue presented the typical morphology. Our results suggest that CoCl2 is able to induce local apoptotic activity in the brain tissue exposed to the drug. The localized damage makes this model really useful to induce a very focal brain injury. Supported by UBACYT Grant M-072

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