The Change of Neuropathic Pain and Pain Related Gene Expression following Exposure to Chronic Smoking

Abstract

Background: Several studies have reported reduced pain and anxiety in smokers, and considerable evidence shows that smoking induces analgesia, which is thought to be nicotine-mediated. We investigated if smoking could reduce the development of neuropathic pain and nociceptive transmission in the spinal cord. Methods: Sprague Dawley rats weighing 130-150 g were used for this experiment. The Animals were divided into two groups: the smoking group (S group) was exposed to cigarette smoking for 5 hours per day for 6 weeks at self-made smoking chamber: the control group (C group) was exposed to room air. After a 4-week exposure period, neuropathic pain was induced by left L5 spinal nerve ligation (SNL). Mechanical threshold and withdrawal response to 100% acetone were measured throughout the experiment. The changes in the expression of the c-fos and BDNF genes in the spinal cord were compared using real time PCR. Results: Mechanical allodynia was induced after SNL in both groups, but no significant difference was observed between two groups. Cold allodynia after SNL was significantly less in S group than C group. In S group, the expression of c-fos was decreased at 5th day, but that of BDNF expression was significantly elevated at 5th day after SNL compared to C group. Conclusions: Chronic exposure to cigarette smoke reduced the cold allodynia in neuropathic rats. The decreased expression of c-fos and elevated expression of BDNF in the spinal cord after SNL may contribute to antinociception.