Pain and analgesia: The dual effect of nitric oxide in the nociceptive system.

Nitric oxide (NO) is involved in many physiological processes and several lines of evidence have indicated that NO plays a complex and diverse role in the modulation of pain. Nitric oxide is an important neurotransmitter involved in the nociceptive process and, in the dorsal horn of the spinal cord, it contributes to the development of central sensitization. On the other hand, experimental data have also demonstrated that NO inhibits nociception in the peripheral and also in the central nervous system. In addition, it has been shown that nitric oxide mediates the analgesic effect of opioids and other analgesic substances. The information included in the present review aims to present and analyze data about the dual effect of NO on pain transmission and control, the molecular mechanisms involved in these effects and also the potential use of nitric oxide in pain therapy.