The effect of a 5-HT2A receptor antagonist on pain-related behavior, endogenous 5-hydroxytryptamine production, and the expression 5-HT2A receptors in dorsal root ganglia in a rat lumbar disc herniation model.

Abstract

Controlled, interventional, animal study. To evaluate the effect of a 5-HT2A receptor antagonist on pain-related behavior, endogenous 5-hydroxytryptamine (5-HT) plasma levels, and expression of 5-HT2A receptors in dorsal root ganglia (DRGs) in a rat lumbar disc herniation model. Application of nucleus pulposus on the nerve root induces immediate peripheral 5-HT production and the expression of 5-HT2A receptors in the adjacent DRG. However, the efficacy of a 5-HT2A receptor antagonist for pain relief in this situation and the mechanism remain unknown. Autologous nucleus pulposus was applied to the left L5 nerve root of 91 adult female Sprague-Dawley rats. The selective 5-HT2A receptor antagonist sarpogrelate hydrochloride (SPG; 1 mg/kg or 10 mg/kg) or vehicle was administered orally once a day from 1 to 21 days postoperatively. Von Frey tests were used to test pain behavior before and after surgery. To assess the effect of SPG on endogenous 5-HT release surrounding the inflamed nerve root, we measured levels of 5-hydroxyindole acetic acid, a 5-HT metabolite, in plasma. Expression of 5-HT2A receptors in the left L5 DRG was examined with immunoblotting. The higher dose (10 mg/kg) of SPG significantly improved the mechanical withdrawal thresholds from 5 to 21 days after surgery compared with vehicle treatment. 5-hydroxyindole acetic acid in plasma was not significantly different among any groups at any time points. Both doses of SPG inhibited the expression of 5-HT2A receptors after surgery compared with vehicle treatment. A selective 5-HT2A receptor antagonist attenuated pain-related behavior and suppressed 5-HT2A receptor expression in the DRG, but did not affect peripheral 5-HT production. Selective 5-HT2A receptor antagonists may attenuate sciatica by blocking and downregulating 5-HT2A receptors in DRGs in lumbar disc herniation. NA.