The present study demonstrated that TMP by intravenous administration before or after aortic occlusion significantly ameliorates transient spinal cord ischemia (20 min) produced by occlusion of the infrarenal aorta in rabbits. No obvious dose-response effect was observed within the dose range studied in the present study.
Partial to complete paralysis during the early postoperative period is an unfortunate and unpredictable consequence of operation on the descending thoracic or thoracoabdomina aorta or direct spinal cord surgery for tumors. Neurologic deficits may be noted during the immediate postoperative period or may be manifested many hours after operation, which severely affluences surgical outcome, and leads to massive psychological and financial burden. Multiple studies [3–6] have been done to examine the effects of various pharmacologic agents on spinal cord ischemia, but no clinically effective treatments have yet been developed. TMP, one of the alkaloids in ligusticum Wallichii Franch (L. Wallichill), an active ingredient in Chuanxiong, has been widely used, especially in the treatment of patients with cerebrovasular ischemic diseases in China and manifested its therapeutic actions in clinic [14, 15]. TMP has been demonstrated to provide significant protective properties against acute brain ischemic injury induced by ligation of bilateral common carotid arteries (2VO) in gerbils and cerebral infarction produced by middle cerebral artery occlusion (MCAO) in rats in experimental studies [11, 12], but limited data exist regarding the use of TMP in spinal cord injury. The rabbit model of spinal cord ischemia used in this study, which mimics aortic occlusion during operation on the thoracoabdominal aorta in clinic, is a reliable and reproducible model for producing neurologic deficit and testing drugs that might serve to protect the spinal cord from ischemic injury .
There was significant improvement in the neurologic outcomes of rabbits that received TMP comparing with the control group. Both protective group and treated group with the same dose of TMP had higher Tarlov scores than that in the control animals. Animals treated with TMP before aortic occlusion had 100% recovery at 48 h. These animals were able to stand without difficulty and hop normally. Except for one rabbit treated with TMP at the onset of reperfusion, other animals reached a median Tarlov score of 3 after 48 h with standing or hopping. In contrast, control animals showed paralysis of the hind limbs. It was confirmed in present study that the motor function scores at different time points and the number of normal neurons in the anterior spinal cord at 48 h in the two groups received treatment of TMP 30 and 60 mg·kg-1 after reperfusion were significantly better and greater respectively than those in the control group. Animals treated with 15 mg·kg-1 TMP did not show any neurologic and histopathologic improvements, indicating a enough dose of TMP is needed to have therapeutic effect on spinal cord ischemic injury. These results are not consistent with a recent study  examining the protective effects of TMP on cerebral infarction produced by middle cerebral artery occlusion (MCAO) in rats. Cen et al  demonstrated that TMP 10, 20, 40 mg·kg-1 given intravenously markedly improved the abnormal nervous symptoms in rats, significantly reduced the infarct volume at 24 h after MCAO, and presented a certain dose-response relation. This study showed that lower dosage of TMP produced inadequate protective effects against ischemic spinal cord injury. The differences may be result of different animal species and model.
Histologic examination confirmed the ability of TMP to limit neuronal degeneration and necrosis in the anterior horn motor neurons. Histologic examination of the spinal cords revealed either no evidence or very little evidence of injury in TMP-prevented rabbits, whereas spinal cords from control animals had evidence of extensive spinal cord injury with central gray matter necrosis, perikaryal swelling, vacuolization of anterior horn motor neurons, Nissl substance dissolution, and karyolysis. These morphologic changes developed after ischemia and caused the physiologic and clinic consequences observed after ischemic disturbance. The number of normal neurons at anterior spinal cord has direct relations with neurologic function, which was manifested by a strong correlation between the final neurologic outcomes and the number of normal neurons at anterior spinal cord.
The mechanism of motor neuronal cell death after spinal cord ischemia and reperfusion has been explored through molecular, cellular and genic aspects, but it has not been yet identified. Evidence is gathering that a various of factors induced over-accumulation of intracellular calcium triggers proteases, lipase, protein kinase C, nitric oxide synthase, endonucleases, altered gene transcription, and release of free radicals, eventually producing neuronal injury and death. The present study did not explore the protective mechanism of TMP on motor neurons after spinal cord ischemia. According to pharmacology of TMP and studies for effects of TMP on cerebral ischemic injury, antiplatelet activation and aggregation, dilating arterioles to improve microcirculation [17, 18], scavenging free radicals, increasing the activity of SOD and decreasing lipid peroxidation , inhibiting calcium overload , reducing the production of nitric oxide and dynorphin A1-13 in ischemic tissue [19, 20], decreasing the protein expression of c-fos and increasing the protein expression of bcl-2 and heat shock protein 70(HSP 70) [21, 22]may be mechanisms for protection of TMP against spinal cord ischemia /reperfusion injury. The injection of TMP is a pure extract from Chinese herbs, and has the properties of abundant resources, cheapness, wide range of dose in clinic and few side effects. Thus we anticipate that TMP might have important clinical application as a treatment in the prevention of spinal cord injury during thoracoabdominal aortic operations.