Nylon Monofilament for Intraluminal Middle Cerebral Artery Occlusion in Rats

Background and Purpose In rat middle cerebral artery (MCA) occlusion models with an intraluminal nylon monofilament, lesion volume and its reproducibility vary among laboratories. These variations may be caused by differences in the properties of nylon monofilaments. We performed the present study to compare the effects of two different types of 4-0 nylon monofilament on neurological and morphological outcomes in this model. Methods We randomly and blindly used two types of 4-0 nylon monofilament (Ethilon, n=15, and Nitcho, n=15) to permanently occlude the ostium of the right MCA intraluminally in rats. Neurological outcome and lesion size were compared 24 hours after MCA occlusion between the two groups. The diameter, tensile strength, and extensibility of each filament were measured. Results Neurological outcome was not different between the groups. The mortality within 24 hours was 13% (2/15) in the Ethilon group and 0% in the Nitcho group. Total lesion volume in the former was 295.9±97.2 mm 3 (mean±SD), significantly larger and more reproducible than that in the latter (190.3±144.7 mm 3 , P =.026). The Ethilon filament had a significantly larger diameter (Ethilon, 0.193±0.001 mm; Nitcho, 0.180±0.001 mm; P <.0001), poorer tensile strength, and better extensibility than the other. Conclusions Exact diameter and quality are not always the same among nylon monofilaments, even if they meet the standard for the designation 4-0. The present study indicates that slight differences of filament characteristics significantly affect lesion volume and its reproducibility. This result may explain some conflicting observations in this MCA occlusion model.