Experimental stroke:: ischaemic lesion volume and oedema formation differ among rat strains (a comparison between Wistar and Sprague-Dawley rats using MRI)

Investigating focal cerebral ischaemia requires animal models that are relevant to human stroke. This study was designed to evaluate the influence of early reperfusion and choice of rat strains on infarct volume and oedema formation. Thirty-six Wistar and Sprague-Dawley rats were subjected to temporary middle cerebral artery occlusion (MCAO) for 90 min (groups I and II) or to permanent MCAO (groups III and IV) using the suture technique. Ischaemic lesion volume and oedema formation were quantified 24 h after MCAO using 7T-magnetic resonance imaging (MRI). Impact of rat strains: Reperfusion led to significant larger ischaemic lesion volumes in Wistar rats as compared to Sprague-Dawley rats (P <0.0005). Oedema formation was similar in both rat strains. Permanent MCAO led to significantly larger ischaemic lesion volumes in Sprague-Dawley rats P <0.05). Oedema formation, however, was significantly more accentuated in Wistar rats (P <0.005). Impact of reperfusion: Reperfusion did not cause any changes in ischaemic lesion volume in Wistar rats. Oedema formation, however, was significantly reduced (P <0.0005). In Sprague-Dawley rats, reperfusion caused a significant reduction of ischaemic lesion volume (P <0.00005), but did not modify oedema formation. These findings emphasize the critical importance of rat strain differences in experimental stroke research.