Focal brain ischemia in rat:: acute changes in brain tissue T1 reflect acute increase in brain tissue water content

Several recent studies have reported changes of brain tissue T-1 in ischemic models during the first minutes after occlusion of the middle cerebral artery (MCA). In order to assess whether these tissue T-1 changes are related to an increase in tissue water content, we performed T-1 (7 T) and tissue water content measurements in a rat model (n = 10, Sprague-Dawley) of focal cerebral ischemia (intraluminal occlusion model). The tissue water content was determined using a gravimetric technique. The animals were divided into two groups: an ischemic group, with an effective MCA occlusion (n = 6) and a control group, with animals having undergone sham surgery but no MCA occlusion (n = 4). In the ipsilateral cortex, the tissue water content was 81.1 +/- 0.7% at 2 h 15 min following ischemic insult (contralateral value: 79.3 +/- 0.5%). Concomitantly, the tissue T-1 in the ipsilateral cortex was 2062 +/- 60 ms at ischemia onset +1 h (contralateral 1811 +/- 28 ms) and 2100 +/- 38 ms at ischemia onset +2 h (contralateral 1807 +/- 18 ms). The tissue T-1 and tissue water content values measured in the contralateral area do not differ from the values obtained in the control group. A significant T-1 increase is observed at ischemia onset +1 h (+ 14%) and ischemia onset (+2 h) + 16%, together with a significant increase in tissue water content (+2.3%). This suggests that there is an increase in tissue water content concomitant with cell swelling during the first hours of ischemia. Copyright (c) 2005 John Wiley & Sons, Ltd.