Background
The embolic MCA occlusion model in rats is used to study recanalisation mechanisms in acute stroke. Next to the determination of morphological lesion size as an outcome parameter, the assessment of functional outcome may improve the value of this animal model. A comprehensive functional testing should allow a discrimination between the degrees of ischemic brain damage. Aim of this study was therefore, to evaluate a neurological score consisting of different sensorimotor tests and a parallel bar crossing test for their correlation with the infarct sizes after embolic MCA occlusion.
Methods
Male Wistar rats were submitted to MCA clot embolism (n=14) or sham surgery (n=7). The emboli were placed by means of a polyethylene catheter (OD 0,28-0,3 mm), that was transiently advanced into the right distal internal carotid artery. In order to achieve a larger variety of lesion size, subgroups were subjected to differently sized emboli (30 and 40 mm in 7 animals, respectively). Animals were followed up every day for 6 days. Outcome assessment consisted of a parallel bar crossing test and a neurological score with ten different items (including different motor, coordinative and sensory functions). Functional impairment was scored from 0 (no impairment) to 100 (no reaction to any stimuli). Animals were perfusion-fixed (4% paraformaldehyde) on postoperative day 7, brains were removed and 3 μm-thick sections were Hematoxylin-eosin stained for quantification of infarct volume (blinded examination).
Results
The infarct volume depended on the initial length of the applied blood clot (clot length 40 mm: 53. 22+/−43.15 mmł, p=0.002 compared to sham; clot length 30 mm: 19.86+/−18.77 mmł, p=0.009). For both subgroups, there was a significant impairment on the neurological score, with only partial improvement during the follow up period and significant impairment on day 6 (clot length 40 mm: 41.4+/−13.1, p=0.001 compared to sham; clot length 30 mm: 25.7+/−16.2, p=0.003). On follow up day 6, there was a highly significant correlation between the determined infarct volume and the functional outcome (R=0.80, p=0.0006). There were statistically significant functional deficits for both subgroups on the parallel bar crossing test (traversing time and number of foot faults) during the complete follow-up period. The correlation with infarct volume was significant up to day 4 (traversing time: R=0.55, p=0.01; foot faults: R=0.60, p=0.004), but failed significance on day 6 (traversing time: R=0.25, p=0.38; foot faults: R=0.38, p=0.18).
Conclusions
In this embolic MCA occlusion model, application of emboli with a clot length of 40 mm is superior to 30 mm with regard to reliability and extent of lesion size and with regard to the degree and persistence of the functional impairment during the evaluated follow-up period. We present outcome tests that provide quantitative and objective tools to test functional impairment in rats following embolic stroke. Best results are achieved with a neurological deficit score which is easy to perform and correlates significantly with infarct volume. We conclude that functional outcome testing may serve as a complementary evaluation tool in recanalisation studies of embolic stroke in rats.