Serotonergic 5-HT Receptors as Modulators of the Nociceptive System.

The biogenic amine serotonin modulates pain perception by activating several types of serotonergic receptors, including the 5-HT type. These receptors are widely expressed along the pain axis, both peripherally, on primary nociceptors, and centrally, in the spinal cord and the brain. The role of 5-HT receptors in modulating pain has been explored in vivo in different models of inflammatory and neuropathic pain. While most studies have reported an antinociceptive effect of 5-HT receptor activation, some authors have suggested a pronociceptive action. Differences in pain models, animal species and gender, receptor types, agonists, and route of administration could explain these discrepancies. In this mini-review, some of the main findings concerning the function of 5-HT receptors in the pain system have been presented. The expression patterns of the receptors at the different levels of the pain axis, along with the cellular mechanisms involved in their activity, have been described. Alterations in receptor expression and/or function in different pain models and the role of 5-HT receptors in controlling pain transmission have also been discussed. Finally, some of the future perspectives in this field have been outlined.