BACKGROUND: The direct current electrical field can effectively promote the regeneration of the spinal cord; moreover, methylprednisolone (MP) can relieve secondary edema after spinal cord injury. Tetrandrine (Tet) is an effective component of hanfangji and can protect the effect of spinal cord and axis-cylinder.Whether direct current electrical field combining with MP or Tet has synergic or strengthening effect on treating complete spinal cord injury or not should be studied further.OBJECTIVE:To study the effect of direct current electrical field assisted by MP and Tet on treating spinal cord injury.DESIGN: Randomized controlled animal study.SETTING: Peoples Hospital of Hainan Province.MATERIALS: A total of 45 healthy hybrid dogs, of both genders, weighing 10 - 12 kg, aged 1.5 - 2 years,were provided by Animal Center of Hainan Province. Somatosensory evoked potential meter (DANTEC Company), IBAS-2.0 imaging analysis meter (Germany), and self-made electronic stimulator.METHODS: The experiment was carried out in Hainan Peoples Hospital from May 2001 to June 2004. All experimental dogs were randomly divided into 4 groups: control group (n =9), electrostimulating group (n =12), MP + electrostimulating group (n =12) and Tet + electrostimulating group (n =12). ① After anesthesia, Allen WD method was used to induce complete spinal cord injury. The metal bar, which was 10cm in height fell freely and vertically hit the spinal cord to provide a complete spinal cord injury. Dogs in control group and electrostimulating group were implanted electrical stimulators 6 hours after spinal cord injury (no electricity in control group); dogs in MP + electrostimulating group were injected 30 mg/kg MP for 15 minutes at 2 hours after spinal cord injury and electrical stimulators implanted at 6 hours after injury;dogs in Tet + electrostimulating group were intravenously injected with 7.5 mg/kg Tet at 2 hours after spinal cord injury and electrical stimulators implanted at 6 hours after injury; and then, 7.5 mg/kg Tet injected at days 2 and 3 after injury. ② Specimens were taken from control group from three dogs of every month;from the injured segments of spinal cords at 1 month, 2 months and 3 months; and from electrostimulating group, MP + electrostimulating group and Tet + electrostimulating group of 4 dogs for histological examinations. ③ Detection of neurological function: Neurological function was evaluated with the functional 10 grading system. The scores ranged from 0 to 10 (0: complete paraplegia; 10: normality). ④Detection of cortical somatosensory evoked potential (CSEP): According to the scheme formulated by the International Electroencephalographical Association, the patterns of the fundamental waves were P1 - N1 -P1 waves. The latency of the P1 wave and the amplitude of P1 -N1 waves were mainly observed individually at 1, 2 and 3 months after the injury. ⑤ Histological detection: All spinal cord specimens of the injuried segment were harvested at 1, 2 and 3 months after injury. They were stained with hematoxylin and Nissl staining methods, and then were observed under an optical microscope, and the neurons were counted.The sectional areas of the neurons and the density of the Nissl bodies were measured by a system image pattern analysis (IBAS-2.0, Germany).MAIN OUTCOME MEASURES: The neurological function, cortical somatosensory evoked potential,neuronal amount, sectional area of neurons and Nissl body density at 1 to 3 months after injury.RESULTS: All 45 experimental dogs were involved in the final analysis. ① Detection of neurological function: One month later, the dogs in MP + electrostimulating group could walk, but the dogs in electrostimulating group and Tet + electrostimulating group could stand. Two months after injury, the dogs in MP + electrostimulating group almost recovered to normal, but the dogs in electrostimulating group could walk and those in Tet + electrostimulating group could run. Those in control group had no parent recovery.② Detection of P1 latency and P1 -N1 amplitude: Changes of P1 latency in control group were long and P1 -N1 amplitude was very low at 1 month later. Compared to electrostimulating group, MP +electrostimulating group and Tet + electrostimulating group, there were significant differences (P ＜ 0.05). P1latency was manifestly shortened and amplitude were raised in electrostimulating group, MP +electrostimulating group and Tet + electrostimulating group. Those in MP + electrostimulating group and Tet + electrostimulating group were superior to those in electrostimulating group and there were significant differences (P ＜ 0.05). ③ Sectional areas of neurons and Nissl body density: At 1 - 3 months after injury, sectional areas of neurons were larger in electrostimulating group [(170.14 ± 7.45), (209.60 ±14.80), (312.47± 12.63) μm2], MP + electrostimulating group [(282.18± 15.25), (418.18± 16.27), (515.25±15.10) μ m2] and Tet + electrostimulating group [(231.81±7.38), (322.67±8.45), (386.82±10.42) μm2] than control group[(98.12±4.93), (113.50±6.74), (122.59±8.03) μ m2, P ＜ 0.05]; especially, sectional area was the largest in MP + electrostimulating group. At 1 - 3 months after injury, Nissl body density was more in electrostimulating group (170.14 ± 7.45, 209.60± 14.80, 312.47 ± 12.63), MP + electrostimulating group (282.18± 15.25, 418.18± 16.27, 515.25 ± 15.10) and Tet + electrostimulating group (231.81 ±7.38,322.67±8.45, 386.82±10.42) than control group (98.12±4.93, 113.50±6.74, 122.59±8.03, P ＜ 0.05);especially, Nissl body density was the most in MP + electrostimulating group.CONCLUSION: The direct current electrical field can effectively promote spinal cord regeneration. The combination of direct current electrical field with large dose MP or Tet has synergistic effects for treating spinal cord injury. The curative effects of direct current electrical field with large dose MP are much better than those with Tet.