Effect of lacosamide on expression of Nav1.8 in dorsal root ganglia in a rat model of chronic neuropathic pain

Objective To investigate the effect of lacosamide on expression of Nav1 .8 in dorsal root ganglia (DRG) in a rat model of chronic neuropathic pain.Methods Thirty-six female specific-pathogen-free (SPF)SD rats were randomly assigned into 3 groups ( n = 12 each): sham operation group (group S), model group (group M) and lacosamide group (group L) . Chronic neuropathic pain was produced by insertion of a small stainless steel rod (4.00 mm in length and 0.63 mm in diameter) into the L, intervertebral foramen in the rat, producing a chronic steady compression of the DRG in M and L groups. The mechanical threshold was measured 2 days before operation and on the 2, 4, 6, 7, 8, 9 and 10 days after operation (T0-7 ) . Intraperitoneal lacosamide 20mg/kg (in normal saline 0.5 ml) was injected at T4-7, twice a day in S and L groups. In group M, normal saline 0.5 ml was injected at T4-7 twice a day and the mechanical threshold was measured after the last administration everyday . The L, DRG on the operated side was removed after measurement of pain threshold to detect the expression of Na, 1.8 mRNA and protein by RT-PCR and immuno-histochemistry respectively. Results Compared with group S, the mechanical pain threshold was significantly decreased at T1-7 and the expression of Navl .8 mRNA and protein was up-regulated in M and L groups ( P < 0.05) . Compared with group M, the mechanical pain threshold was significantly increased at T4-7 and the expression of Nav 1.8 mRNA and protein was down-regulated in group L ( P < 0.05) . Conclusion The mechanism by which lacosamide reduces chronic neuropathic pain is related to the down-regulation of the expression of Nav 1.8 in rat DRG. Key words: Acetamides;  Sodium channels;  Ganglia, spinal;  Neuralgia