Mediation of spinal nerve injury induced tactile allodynia by descending facilitatory pathways in the dorsolateral funiculus in rats

Evidence exists to indicate that tactile allodynia arising from peripheral nerve injury is integrated predominately at supraspinal, rather than spinal , sites. In the present experiments, the possibility that disruption of des cending pathways through the dorsolateral funiculus (DLF) might alter expre ssion of nerve-injury induced tactile allodynia was explored. Male, Sprague -Dawley rats received L-5/L-6 spinal nerve ligation (SNL). Lesions to the D LF were made ipsilateral or contralateral to SNL, Tactile allodynia was det ermined by measuring withdrawal thresholds to probing with von Frey filamen ts. Rats with DLF lesions presented no apparent motor deficits acid did not alter sensory threshold in sham-SNL operated rats. DLF lesions made ipsila teral to SNL completely blocked tactile allodynia in SNL rats. Contralatera l DLF lesions and sham surgery did not have any effect on SNL-induced allod ynia. These results indicate that tactile allodynia after peripheral nerve injury is dependent upon tonic activation of net descending facilitation fr om supraspinal sites and support the hypothesis of tonic activation of desc ending facilitation as a basis for chronic pain. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.