The Effect of Intrathecal Administration of Carbenoxolone and Muscimol on Chemical Pain in Rats Underwent C-fiber Removal Process

Abstract

Background and Objectives: Spinal cord dorsal horn lamina 2 receives many synaptic terminals from C fibers and a few from Aβ fibers. GABAergic inhibitory interneurons in lamina 2 play an important role in the pain sensation. Gap junctions (Gj) are intercellular channels, which provides cell to cell transport of small molecules and ions. In this research, the importance of C-fibers in pain transmission through GABAergic system and Gj manipulations, was investigated by formalin test using capsaicin, muscimol, and carbenoxolone. Methods: In this experimental study, 9 groups of male wistar rats (200-250 g), including group treated with capsaicin in infancy, control group, and sham group, were used. Adult animals received saline, carbenoxolone (1nM) and muscimol (0.3μg) individually or as a form of co-treatment. After sub plantar injection of 0.05 ml of 2.5% formalin, pain related behavior was recorded for 1 hour. Data were compared using one-way ANOVA and post t-Tukey test. Significance level was considered to be p<0.05. Results: Analgesic effect was the same in groups treated in infancy with capsaicin, and received saline and carbenoxolone, but muscimol increased pain reduction in the inflammatory phase of formalin test (p<0.01). Also, Co-treatment of carbenoxolone and muscimol did not show more pain reduction. Conclusion: Considering the elimination of C-fibers and stimulation of GABA-A, elimination of Gj cannot show a significant effect on pain relief beyond what the elimination of C-fibers and stimulation of the GABAergic system at the spinal level can do.

Keywords

• pain
• nerve fibers
• unmyelinated
• carbenoxolone
• muscimol