(642): Spinal nerve ligation-induced allodynia is dependent on the NFκ-B-mediated induction of spinal COX-2 and prostaglandin synthesis in the rat

Abstract

L5/L6 spinal nerve ligation (SNL) induces early, spinal prostaglandin (PG)-dependent allodynia (<10 days after injury), including the increased expression of COX-2 in the ipsilateral lumbar dorsal horn 3 days after SNL. This study investigated the spinal expression of nuclear factor κ-B (NFκ-B; a modulator of COX-2 transcription), its relationship to the induction of COX-2, and the respective contributions of NFκ-B and COX-2 in the development of SNL-induced allodynia. Male, Sprague-Dawley rats (100-140g), fitted with intrathecal (i.t.) catheters, underwent SNL- or sham-surgery. Allodynia was defined as a paw withdrawal threshold (PWT) of ≤4g (baseline ≥15g). The biceps femoris flexor reflex was measured electromyographically, and lumbar segments were analyzed for NFκ-B and COX-2 protein expression. Allodynia and A- and C-fibre hyperexcitability (i.e. decreased activation threshold, increased evoked activity, including windup; p<0.05) were evident 3 days after SNL- but not sham-surgery. NFκ-B expression was increased in the ipsilateral, but not contralateral, dorsal horn of allodynic animals. This was apparent 12h after SNL and remained elevated at 3 days (p<0.05). Sham-surgery had no effect on NFκ-B (p>0.05). The NFκ-B inhibitor, ammonium pyrrolidinedithiocarbamate (PDTC; 100μg i.t.), given immediately after SNL, decreased A- and C-fibre hyperexcitability 3 days later (p<0.05), and prevented the development of allodynia. Hyperexcitability was dose-dependently attenuated by i.t. SC-236 (COX-2 inhibitor), but not SC-560 (COX-1 inhibitor), given 3 days after SNL. Treatment with i.t. COX-inhibitors, immediately after SNL, also prevented the development of allodynia with no apparent effect on NFκ-B activation. These results indicate that: 1) the SNL-induced expression of spinal COX-2 is modulated by NFκ-B; 2) the hyperexcitability/allodynia observed 3 days after SNL is spinal PG-dependent; and 3) spinal COX-2 is primarily responsible for PG synthesis at this time point. While NFκ-B activation is a critical intermediate step, its influence on SNL-induced allodynia reflects the consequent actions of spinal PGs. L5/L6 spinal nerve ligation (SNL) induces early, spinal prostaglandin (PG)-dependent allodynia (<10 days after injury), including the increased expression of COX-2 in the ipsilateral lumbar dorsal horn 3 days after SNL. This study investigated the spinal expression of nuclear factor κ-B (NFκ-B; a modulator of COX-2 transcription), its relationship to the induction of COX-2, and the respective contributions of NFκ-B and COX-2 in the development of SNL-induced allodynia. Male, Sprague-Dawley rats (100-140g), fitted with intrathecal (i.t.) catheters, underwent SNL- or sham-surgery. Allodynia was defined as a paw withdrawal threshold (PWT) of ≤4g (baseline ≥15g). The biceps femoris flexor reflex was measured electromyographically, and lumbar segments were analyzed for NFκ-B and COX-2 protein expression. Allodynia and A- and C-fibre hyperexcitability (i.e. decreased activation threshold, increased evoked activity, including windup; p<0.05) were evident 3 days after SNL- but not sham-surgery. NFκ-B expression was increased in the ipsilateral, but not contralateral, dorsal horn of allodynic animals. This was apparent 12h after SNL and remained elevated at 3 days (p<0.05). Sham-surgery had no effect on NFκ-B (p>0.05). The NFκ-B inhibitor, ammonium pyrrolidinedithiocarbamate (PDTC; 100μg i.t.), given immediately after SNL, decreased A- and C-fibre hyperexcitability 3 days later (p<0.05), and prevented the development of allodynia. Hyperexcitability was dose-dependently attenuated by i.t. SC-236 (COX-2 inhibitor), but not SC-560 (COX-1 inhibitor), given 3 days after SNL. Treatment with i.t. COX-inhibitors, immediately after SNL, also prevented the development of allodynia with no apparent effect on NFκ-B activation. These results indicate that: 1) the SNL-induced expression of spinal COX-2 is modulated by NFκ-B; 2) the hyperexcitability/allodynia observed 3 days after SNL is spinal PG-dependent; and 3) spinal COX-2 is primarily responsible for PG synthesis at this time point. While NFκ-B activation is a critical intermediate step, its influence on SNL-induced allodynia reflects the consequent actions of spinal PGs.