MRI/histological correspondence during the resolution phase of edema. A representative rat examined at 20 dpi is shown. (A) MRI showed a small cavitation at the site of the injection with a cerebrospinal-fluid-like signal on the T2WI (arrow) and ADC map, while no peripheral edema was anymore visible along the upper part of the internal capsule (dotted line, ADC = 889 μm2/s as opposed to 852 μm2/s in the symmetric contralateral area). (B) The corresponding histological sections (low magnification, with white boxes indicating higher magnification positions) showed a marked increase in AQP4 immunoreactivity, with staining located around the vessels (arrowhead) and with a fibrillary pattern corresponding to staining on the entire astrocyte membrane in a gliotic area (arrows). The staining in the symmetric contralateral area is more faint and only around capillaries. (C) Double labeling of GFAP (Alexa 488, green) and AQP4 (CY3, red), examined using confocal microscopy, confirmed AQP4 localization over the entire membrane of hypertrophic astrocytes expressing high levels of GFAP and not just around vessels (arrowhead). Double arrows show AQP4 staining along an astrocyte process and dotted arrows show AQP4 staining along an astrocyte cell body.