A Modified Model for Rat Sciatic Nerve Ischemia/Reperfusion Injury

Abstract

Sir: A number of different models of unilateral ischemia/reperfusion injury in rat sciatic nerve have been developed. In one method described by Mitsui et al.,1 the abdominal aorta, the right iliac and femoral arteries, and all identifiable collateral vessels supplying the right sciatic-tibial nerve are ligated for 3 hours and then reperfused for different time intervals. In another model introduced by Saray and his colleagues,2 only the femoral artery and vein–-just distal to the inguinal ligament–-are clamped for 3 hours, followed by reperfusion. The first method is time-consuming and requires advanced surgical techniques and instruments, and the second one, albeit easy to perform, does not produce severe injury.3 The aim of this study was to develop a practical model producing serious neurologic deficits that was still technically feasible. For this purpose, clamping of the femoral artery as well as the ipsilateral common iliac artery was used to induce sciatic nerve ischemia/reperfusion. For this pilot study, 12 Sprague–Dawley male rats weighting 150 to 200 g were randomly divided into two groups: the sham-operated group and the ischemia/reperfusion group. All animals were anesthetized with ketamine (50 mg/kg) and xylazine (4 mg/kg) and subjected to laparotomy. In the ischemia/reperfusion group, the right common iliac artery and the femoral artery–-just distal to the inguinal ligament–-were clamped for 3 hours using two Yasargil aneurysm clips providing 125 g (1.24 N) of force. By using a thermal pad, the deep rectal temperature was monitored by a rectal probe inserted 5 cm into the rectum and maintained at 36.5°C ± 1°C. All procedures were carried out for the sham-operated group, but arterial clamping was excluded. After 1 week of reperfusion, each animal's behavioral score was assessed based on gait, grasp, paw position, and pinch sensitivity; the score for each index was based on a scale of 0 (no function) to 3.0 (normal function), except for pinch sensitivity, the score for which ranged from 0 to 2.1 Then, the sciatic nerve was fixed in situ for 30 minutes using 4% formaldehyde in phosphate buffer (pH adjusted to 7.4), and then trifurcation of the sciatic nerve was removed, the nerve was embedded in paraffin, and sections were stained with hematoxylin and eosin and trichrome Gomori for light microscopy studies. The median behavioral scores were 5 and 11 in the ischemia/reperfusion and sham groups, respectively, and were significantly different (p < 0.05, Mann-Whitney U test). The pathologic markers for ischemia/reperfusion, including epineurial and endoneurial edema and demyelination in trichrome Gomori staining, were observed in the ischemia/reperfusion group but were absent in the sham-operated group (Figs. 1 and 2).Fig. 1.: Transverse section of the rat sciatic nerve after 7 days of reperfusion shows epineurial and endoneurial edema (hematoxylin and eosin stain).Fig. 2.: Transverse section of the rat sciatic nerve after 7 days of reperfusion shows epineurial and endoneurial edema and demyelination (trichrome Gomori stain).Our results show that common iliac artery and femoral artery clamping induces ischemia/reperfusion injury in the rat sciatic nerve. This method offers the obvious advantage of producing an easily inducible, moderate to severe neurologic deficit compared with current methods. However, a more comprehensive study containing several groups of different reperfusion intervals and quantification of pathological changes is needed to make the method practical for use in experimental studies. Mohammad R. Rasouli, M.D. School of Medicine Mohsen Nouri, M.D. School of Medicine Reza Rahimian, Ph.D. Department of Pharmacology Fahimeh Asadi Amoli, M.D. Trauma and Surgery Research Center Vafa Rahimi-Movaghar, M.D. Trauma and Surgery Research Center Ahmad R. Dehpour, Ph.D. Department of Pharmacology School of Medicine Medical Sciences/Tehran University Tehran, Iran