Impaired functionality of reperfused brain tissue following short transient focal ischemia in rats

Functional magnetic resonance imaging (fMRI) has been applied to study the consequences of transient focal ischemia on neuronal excitability in the rat brain. The experimental paradigm consisted of measuring the changes in local cerebral blood volume (CBV) induced by systemic infusion of the GABAA antagonist bicuculline after occlusion of the middle cerebral artery (MCA) for durations of 5, 15, 30 and 60 min using the intraluminal thread model. fMRI studies were carried out 60 min after successful reperfusion of the ischemic territory. Bicuculline-induced dynamic changes in local CBV were assessed in three brain regions: Parietal cortex, caudate putamen and thalamus. The measured CBV response was negatively correlated with the ischemia duration. Additionally, the three regions showed different vulnerability to the transient MCA occlusion, caudate being the most susceptible followed by parietal cortex and thalamus. The fMRI signals weakly correlated with basal CBF and CBV following reperfusion. Our results indicate that fMRI is a sensitive method to assess functional integrity of the brain. Activation maps allow to quantitatively assess the functionally compromized territory at an early stage following the ischemic event prior to the manifestation of pathomorphological changes.