Cooling, or cool-feeling chemicals, may offer a new way to alleviate chronic neuropathic pain following nerve injury, which cannot be effectively treated with current painkillers.

Cooling has a long history in pain relief. It has traditionally been used to ease chronic back pain, dental pain and muscular injuries, while many people rub preparations containing cool-feeling substances such as menthol and mint oil to relieve headaches or neuralgia. However, no mechanism has so far been linked to cooling-induced pain relief.

Now, Susan Fleetwood-Walker, Rory Mitchell and colleagues at the University of Edinburgh have discovered the mechanism by which cooling may be influencing pain. Several cooling receptors exist on sensory neurons and one of these, TRPM8, was found to be responsible for lowering pain responses in the rat.

Activation of TRPM8 inhibited the sensitisation of neurons in key areas of the central nervous system that are responsible for establishing chronic pain. When TRPM8 was specifically eliminated from sensory neurons, cooling and cool-feeling substances no longer had any impact on pain sensitivity.

Chronic pain from nerve damage is a debilitating, difficult-to-manage condition. TRPM8 may be an important target for new, much-needed analgesics.

Image: Hippocrates recommended "a copious affusion of cold water" for pain in the joints and swellings.

External links

• Proudfoot CJ et al. Analgesia mediated by the TRPM8 cold receptor in chronic neuropathic pain. Curr Biol 2006;16(16):1591–605.