Abstract
Neutral red staining was evaluated as an acute outcome assessment method in rat models of cerebral ischemia by comparison with histological infarction volume. Fischer 344 rats (n = 48) were used in three different models of middle cerebral artery (MCA) occlusion: proximal MCA occlusion (n = 16), distal MCA occlusion followed by ipsilateral common carotid artery (CCA) occlusion (distal MCA/ CCA occlusion, n = 15), and MCA occlusion with an intravascularly introduced 4-0 nylon suture (intravascular MCA occlusion, n = 17). At 1 hour, 2 hours, and 4 hours after MCA occlusion, animals were injected with 2.5 ml of 4% neutral red solution via the femoral vein, and then sacrificed. Proximal MCA occlusion caused a neutral red defect volume in the cortex which correlated well with histological infarction volume at 4 hours (r = 0.88, p < 0.05), and in the caudate which correlated well with infarction volume at 4 hours (r = 0.94, p < 0.01). Distal MCA/CCA occlusion caused a neutral red defect volume in the cortex lager than the histological infarction volume (4 hrs: 88.6 ± 11.8 vs. 74.3 ± 17.4 mm3, p < 0.05) but closely correlated with the infarction volume at 4 hours (r = 0.81, p < 0.05). Intravascular MCA occlusion caused a neutral red defect volume in only two of 17 animals after 1-4 hours, which correlated well with the absence of histological evidence of infarction. Neutral red staining is a simple method for assessing the acute outcome of focal cerebral ischemia as early as 4 hours after the onset, in an appropriate model of cerebral ischemia.
