Effect of Thalidomide on Neuropathic Pain Induced by Lumbar 5 Ventral Rhizotomy in Rats

Selective injury to motor fiber but keeping primary sensory neuron intact also induced behavioral signs of neuropathic pain. The underlying mechanism, however, is still unclear. Accumulating evidence showed that TNF- a plays an important role in the process of injured nerve degeneration and the production of abnormal pain behaviours after nerve injury. The present study was to examine the role of TNF-a in the development of neuropathic pain in- duced by lumbar 5 ventral rhiwtomy (L5 VR), a model of selective injury to motor fibre in sciatic nerve, with in- traperitoneal injection of thalidomide, an inhibitor of TNF-a synthesis, started before and after the surgery. The re- sults showed that L5 VR induced robust and long-lasting abnormal pain behaviours in bilateral hind paws of rats. Compared with sham operated group and the pre-operated baseline, the significantly decrease of paw withdrawal threshold and paw withdrawal latency started 1 day after the surgery and persisted more than 4 weeks. Intraperi- toneal injection of thalidomide, started 2 hours before surgery and once per day thereafter, significantly reduced the mechanical allodynia and thermal hyperalgesia in bilateral hind paws induced by L5 VR. Whereas, post-treatment with thalidomide as above started at the 7th day after operation, the established neuropathic pain induced by L5 VR was not affected. Taken together, the above data suggested that TNF-a might be playing an important role in the initiation, rather than maintenance, of the neuropathic pain induced by L5 VT. (Life Science Journal. 2006 ;3( 4) : 12-16J (ISSN: 1097-8135). I I J ,1 ~