A model of global forebrain ischemia/reperfusion in the awake rat

Postischemic reperfusion: ultrastructural blood-brain barrier and hemodynamic correlative changes in an awake model of transient forebrain ischemia

OBJECTIVE

In nonrecovery models of cerebral ischemia, blood-brain barrier (BBB) and cerebral blood flow (CBF) changes are known to occur during reperfusion. It is unknown, however, whether those CBF and BBB alterations occur after brief, transient ischemia with neurological recovery. The purpose of this study was to characterize the time course of CBF and BBB ultrastructural changes during reperfusion in an awake, recovery model of transient global forebrain ischemia (GFI).

METHODS

Forty-five adult Sprague-Dawley rats were subjected, while awake, to 10 minutes of GFI by the nine-vessel occlusion method. Thirty-five age-matched animals composed a sham-operated group. Normal control (n = 5), sham-operated (n = 5), and nine-vessel occlusion/reperfusion (n = 15) rats were selected for ultrastructural analysis. Electroencephalography was performed, and CBF, mean arterial blood pressure, and intracranial pressure were measured during ischemia and reperfusion up to 24 hours. Quantitative morphological analysis of cortical BBB capillaries was performed by transmission electron microscopy at the same time points at which specific CBF changes occurred during reperfusion.

RESULTS

CBF decreased to 6% of preocclusion values during GFI. This correlated with coma and decerebrate rigidity. During reperfusion, short-lived hyperemia (225 +/- 18%, P < 0.001) was characterized by increased intracranial pressure (28.3 +/- 2.6 mm Hg, P < 0.001) and isoelectric electroencephalogram. This was followed by hypoperfusion, which reached a nadir of 59.7% (59.7 +/- 8.8%, P < 0.01) from baseline by 90 minutes. At this time point, the electroencephalogram recovered, and intracranial pressure and mean arterial blood pressure showed no abnormalities. By 8.5 hours, CBF returned to normal, and this coincided with complete recovery of the animal. Ultrastructural BBB analysis revealed astrocyte end-foot process edema and patent capillaries during hyperemia. Severe interstitial BBB edema and capillary lumen collapse was observed during hypoperfusion. Detachment and migration of pericytes was observed during hypoperfusion and beyond.

CONCLUSION

A biphasic CBF response is elicited during reperfusion after brief nonlethal GFI under awake conditions.

Dexamethasone downregulates chemokine receptor CXCR4 and exerts neuroprotection against hypoxia/ischemia-induced brain injury in neonatal rats

OBJECTIVE

Hypoxia/ischemia (H/I) induces rapid and massive brain damage in neonatal rat brain, resulting in long-term consequences on structural and functional maturation of the central nervous system. Inflammatory mediators contribute to these permanent pathological changes, which are sensitive to corticoid treatments. Since the chemokine receptor CXCR4, specific for the SDF-1 alpha/CXCL12 ligand, regulates both apoptotic and neuroregeneration processes, this receptor was quantified 2 days following H/I in neonatal rat brain in relation with dexamethasone (DEX) treatment.

METHODS

Seven-day-old male rats were exposed to a 90-min hypoxia following unilateral carotid ligation (H/I) and were sacrificed 48 h later. Glucocorticoid-pretreated animals were injected subcutaneously 5 h prior to hypoxia with 0.5 microg/g DEX. Glial fibrillary acidic protein and cresyl violet staining were used for assessing the extent of brain lesion subdivided into necrotic and penumbra-like areas. The density of CXCR4 receptors was determined by quantitative autoradiography using [(125)I]SDF-1 alpha as a ligand.

RESULTS

The H/I resulted in a massive lesion ipsilateral to the carotid ligation, which was extended to cortical, striatal, hippocampal and thalamic areas, while the contralateral hemisphere remained apparently unaffected. DEX decreased the lesion size by reducing mainly the necrotic area. H/I induced a marked increase in CXCR4 receptor binding in the penumbra-like areas. DEX pretreatment decreased CXCR4 receptor density in the penumbra and attenuated astrocytosis. Furthermore, DEX strongly lowered mortality rate and reduced functional recovery time right after hypoxia.

CONCLUSION

The rapid enhancement in CXCR4 chemokine receptor binding in the affected brain areas suggests that SDF-1 alpha/CXCR4 may play a role in the hypoxia-induced inflammatory reaction in the neonatal brain. Attenuation of CXCR4 expression and astrogliosis could contribute to the neuroprotective effect of DEX pretreatment via influencing the inflammatory cascade induced by H/I in the neonatal brain.