Figure 2.

Dendritic structure and function in peri-infarct cortex. A, Low-magnification brightfield image of the brain's surface in a YFP-transgenic mouse, two weeks after photothrombotic injury. In this case, the cortical infarction (top left in cranial window) occurred just medial and anterior of the forelimb (FL) and hindlimb (HL) representation of the sensorimotor cortex. B, C, To assess whether peri-infarct cortex was viable, functionally responsive cortex, we imaged intrinsic optical signals after stimulating the contralateral forelimb and hindlimb. After somatic stimulation, certain parts of the cortex appear darker, which is indicative of regionally elevated levels of deoxyhemoglobin (which absorbs the light) as a result of increased neuronal activity (Grinvald et al., 1986). The darker regions were in register with stereotaxic coordinates for forelimb and hindlimb regions. D, Enlarged view of boxed area in A showing cortical areas responsive to forelimb (green) and hindlimb (red) stimulation, superimposed over a brightfield image of the cortical surface. E, To compare the borders of functionally responsive tissue with cortical dendritic structure, the apical dendrites in hindlimb cortex (boxed area in D) were imaged in vivo and tiled together (z projections consisting of 50 planar images, 2 μm apart). As shown in D and E, the border between functionally responsive and nonresponsive cortical tissue corresponds well with the infarct border revealed by YFP-labeled dendrites.