A novel mouse model of stenting ligation to the vessels during the procedure. Once the catheter is inserted into the femoral artery, blood loss is prevented by the oversizing of the catheter compared with the vessel. A small amount of blood does ﬂow through the catheter itself, but this is minimal (less than 5 mL). The procedure has two areas where difﬁculty might occur. First, negotiating the bend between the femoral artery and aorta can be problematic. This is resolved by ensuring the mouse hind leg is as in line with the spine as possible during the procedure to create a straight line between the vessels. Also the outer diameter of the delivery catheter is critical: the tip of the stent protrudes from the catheter to aid insertion into the arteriotomy, and delivery catheters with a small outer diameter have proven more likely to hit resistance at the femoral/aorta branch, possibly due to the mechanics of the tube not holding the aorta wall off the stent itself during insertion. The second procedural problem encountered is permanent leg paralysis in the mouse on recovery. This occurred in 22% of all mice undergoing the procedure, with a higher incidence (13%) during the initial development of the technique. Permanent paraly- sis is avoided by minimal manipulation of the femoral nerve during the procedure and ensuring the nerve is not caught up in any sutures of the vessels. Temporary paralysis of the hind leg upon immediate recovery is more common (29% of all mice) and is caused by the use of the local anaesthetic lidocaine hydrochloride during the procedure. The animals recover from this paralysis within 30 – 60 min post-procedure. Evaluation of the timecourse of stenting showed a progressive development of neointima (Figures 3A and 4 and see Supplementary material online, Figure S1). At 1 day after stenting, polymorphonuc- lear cells are seen around the edge of the stent (Figure 4B). Inﬂamma- tory cells are also seen beneath the stent, in the adventitia. Thrombus formation, containing macrophages, is also evident (Figure 5A). A smooth neointimal accumulation was observed associated with the stent by 3 days. At 7 days, endothelial cells were seen lining the neointima (Figure 4D and 5B), which was still associated mainly with the stent. At 28 days post-stenting, however, a crescentic, organized, and mature neointima, consisting of smooth muscle cells, was seen (Figures 4 and 5). In contrast, sham-stented animals did not develop a neointima in their aorta after 28 days (Figure 4A). Neointimal area along the length of the each part of the aorta con- taining the coil stent was not signiﬁcantly variable (minimum: 0.046, maximum: 0.064 mm2; median: 0.059, SD: 0.008). Internal elastic lamina (IEL) area, mean strut area of each section, and medial thickness remained constant throughout the timecourse (data not shown). There was no change in body weight using this model. To determine the usefulness of the mouse aortic stent model in interventional studies, we examined neointimal formation, 28 days post-stenting, in stented animals that were unable to signal via IL-1. IL-1R12/2 mice subjected to aortic stenting developed signiﬁcantly less neointima than their wild-type control (Figure 3B). Medial thickness, total vessel area, and mean stent strut area did not differ between these two groups. 4. Discussion This is the ﬁrst description of a mouse model of in situ stenting, using a stent speciﬁcally tailored for use in small thin-walled 41 Figure 3 A neointima develops progressively over time (A). Mice deﬁcient in IL-1R1 develop signiﬁcantly less neointima com- pared with wild-type control at 28 days post-stenting (B). arteries. The model is a reliable and reproducible procedure that can be undertaken by a single operator without the need for an advanced level of microsurgical skill. All the vessels are patent at 28 days post-stenting, and a gradual accumulation of neointima is seen over the timecourse of 28 days, which is similar to the pattern seen in other rodent, rabbit, and pig models.5,9 – 21 In addition, neointimal formation in stented animals that are deﬁcient in IL-1 signalling is reduced compared with control animals, in agreement with studies using different models of arterial injury and other animal models of stenting.6,7 Thus, the model described here is comparable with others currently in use and will be useful in interventional studies. The stent used in our model is made from nitinol, a nickel tita- nium alloy that has shape memory. Thus, the stent is a self- expanding coil that reshapes, upon deployment, from the straight wire loaded into the introducer. Such a stent was in common use in human studies in the 1990s, although concerns were raised over toxicity to vascular smooth muscle cells on corrosion22 and the capacity of the stent to continue to expand after deploy- ment.23 In our model, toxicity due to corrosion is not a concern, unless an extended timepoint is investigated, and the constant IEL area of sections throughout the timecourse of stenting, observed in our study, suggests that continued expansion is not occurring.