Objective
To observe the long-lasting changes of pain progression with time course in an autologous nucleus pulposus model of rat. Method: The subjects were 25 Sprague-Dawley (Sprague- Dawley, 250 gm) male rats. They were randomly assigned into either the sham or experimental group. In the experimental group (n=15), autologous nucleus pulposus was harvested from the coccygeal intervertebral disc of the rat and this was grafted on the left L5 dorsal root ganglion. In the sham group (n=10), the left L4 and L5 nerve roots were exposed by laminectomy, but the nucleus pulposus was not grafted. All the rats were evaluated for mechanical allodynia and thermal hyperalgesia at 2 days before surgery, and on days 1, 5, 10, 20, 30, 40 and 50 after surgery. The morphological changes of the spinal nerves were assessed by toluidine blue staining on days 5 after surgery. Results: In the ipsilateral hindpaw of the experimental group, there was a dramatic drop of the mechanical withdrawal threshold and the thermal withdrawal latency on day 1 after surgery, which was maintained at day 50 after surgery. In morphological study, pathological findings such as swelling of the myelin sheath, demyelination, swelling and degeneration of the axoplasm were observed in the spinal nerve at day 5 after surgery. Conclusion: The long-lasting pattern of neuropathic radicular pain shown in a rat model of lumbar disc herniations is helpful to understand the natural history of neuropathic radicular pain due to ruptured nucleus pulposus. (J Korean Acad Rehab Med 2009; 33: 477-482)

Objective
To investigate the characteristics of the central neuropathic pain (CNP) after contusive spinal cord injury in rats. Method: Twenty Sprague-Dawley rats (300⁑50 g, male) undergone the free-drop contusion injury from the drop- height of 2.5 cm at T10 cord (n=20) and ten rats undergone sham operation (n=10) were subjected to the neurobehavioral analyses by the Basso Beattie Bresnahan (BBB) locomotor rating scales, Touch test^TM sensory evaluator (TTSE, North Coast Medical Inc., Canada) and Plantar test^Ⱂ (Ugo Basile, Italy) after contusion at the 1^st, 3^rd, 5^th, 7^th, 14^th, 21^st and 28^th day. Results: The scores of BBB scales were the lowest at the1^st day and then slowly increased to spontaneous recovery state, but they were significantly lower than those of control group (p＜0.05). The thresholds of mechanical allodynia were significantly increased just after cord contusion, but progressed to decline, and significantly decreased after the 21^st day (p＜0.05). The latencies of thermal hyperalgesia were delayed just after cord contusion, but significantly shorter than those of the control group after the 7^th day (p＜0.05). Conclusion: These results would be helpful for the study of the CNP after contusive spinal cord injury in rats. (J Korean Acad Rehab Med 2006; 30: 142-147)