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.

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.

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.

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.