Rat model of spinal cord injury

Rats were randomly assigned into six groups, namely: Sham, model, positive, PMS 80 mg/kg, PMS 40 mg/kg and PMS 20 mg/kg groups. The positive group was treated with methylprednisolone 30 mg/kg as a positive control (17). The ASCI model of rats was established according to Allen's weight hit model (18). Drinking was prohibited until the surgery had been finished. All rats were anesthetized with 3% chloral hydrate (450 mg/kg) by intraperitoneal injection and maintained in the prostrate position for surgery. Fur around the chest and abdomen of these rats was shaved. A 3 cm incision was performed at the position of the eighth thoracic vertebrae and subsequently the dura mater was exposed. A 25 g cm (10 g x 2.5 cm) injury to the spinal cord was set as the injury gravity, which induces a moderate injury (19). Following induction of the injury, the wound was sutured. The following standards were used to evaluate whether a successful rat model was made: i) Spinal cord ischemia and edema around the wound; ii) flicking of the body and legs as well as the appearance of the tail sway reflex, and iii) the above symptoms coupled with sluggish paralysis. To prevent infection of the wound, liquid ampicillin (8 x 10⁵ U/kg; Pureone Bio Technology Co., Ltd.) was injected into the back, exterior muscles once every day, for three days. In order to keep each cage dry, the padding was changed daily. To establish the autonomic urinary reflex of the rats, the bladder was massaged twice per day. Three days after the surgery, all animals were intraperitoneally injected with pentobarbital (200 mg/kg; Beijing Huaye Huanyu Chemical Co., Ltd.) for euthanasia prior to further investigation.