Introduction: Following MCAo, tissue outcome varies depending on depth and duration of hypoperfusion and efficiency of reperfusion. However, the precise time-course of these events in relation to tissue and behavioral outcome remains unsettled due to lack of a wide field-of-view quantitative imaging technique able to map perfusion in the rodent brain at high spatiotemporal resolution. Here we used fUS, a novel approach to map cerebral blood volume (CBV) without contrast agent.
Hypothesis: fUS will allow quantitative, near real-time mapping of CVB during and after tMCAo.
Methods: 45min filament tMCAo was induced in adult SD rats; sham rats were also used. fUS was used to map the penetrating arterioles and venules of the ipsi- and contra-lateral motor (M1-2) and somatosensory (S1) cortex in coronal sections across the MCA territory at 80μm resolution. Three-min coronal scans were taken at different levels before, during and immediately after MCAo, and at 3 and 6 days thanks to a thinned-skull preparation. CBV was expressed relative to mirror ROI. In addition, a 1-hr movie (one frame/5s) was taken starting a few mins after reperfusion. Serial Neuroscore and 2 sensorimotor tasks were given over 3w post-MCAo, and then NeuN, IBa1 and GFAP immunofluorescence (IF) at post-mortem.
Results: fUS showed a ∼80% CBV reduction in S1 during occlusion (p<0.001; n=7), with partial (∼60%, p<0.001) return of CBV on reperfusion, followed by a full return at days 3 and 6. As expected for this model, similar but less conspicuous CBV changes prevailed in M1-2. Continuous reperfusion was depicted in 5/7 rats (slope range: 8-25%/hr relative to prior CBV), but not in 2 rats. There were no significant changes in behavior relative to the sham group (n=4), and IF showed no infarction but marked selective neuronal loss (SNL) in the striatum in 5/7 rats and milder cortical SNL in 4/7 rats.
Conclusions: fUS efficiently mapped the acute changes in CBV during occlusion and following reperfusion with high spatio-temporal resolution, allowing the charting of fine tissue reperfusion dynamics in the individual rat. fUS is ideal to longitudinally map real-time cerebral perfusion in experimental stroke from the hyper-acute through to the chronic stage.