Local hemodynamics dictate long-term dendritic plasticity in peri-infarct cortex.

Changes in dendritic spine turnover are a major mechanism of experience-dependent plasticity in the adult neocortex. Dendritic spine plasticity may also contribute to functional recovery after stroke, but in that setting its expression may be complicated by alterations in local tissue perfusion, especially around the infarct. Using adult Thy-1 GFP-M mice, we simultaneously recorded long-term spine dynamics in apical dendrites from layer 5 pyramidal cells and blood flow from surrounding capillaries with in vivo two-photon microscopy in peri-infarct cortex before and after unilateral middle cerebral artery occlusion. Blood flow in peri-infarct cortex decreased significantly immediately after stroke and improved gradually over time, in a distance-dependent manner from the epicenter of the infarct. However, local tissue perfusion was never fully restored even after a 3 month recovery period. On average, surviving layer 5 pyramidal neurons experienced a ∼20% decrease in spine density acutely after stroke but eventually recovered. The dynamics of this improvement were different depending on the degree of tissue perfusion acutely after arterial occlusion. Cells in ischemic areas closer to the infarct returned to normal spine density levels slowly by retaining spines, while cells in more remote regions with preserved blood flow recovered faster by adding more spines, eventually surpassing baseline spine density by 15%. Our data suggest that maintaining tissue perfusion in the area surrounding the infarct could hasten or augment synaptic plasticity and functional recovery after stroke.