Papers of the Week

The descending serotonergic pathway, from the brainstem to spinal cord, modulates various aspects of pain processing. The spinal 5-hydroxytryptamine (5-HT) and 5-HT receptors play pivotal roles in pain modulation. Perospirone is a novel atypical antipsychotic that serves as a 5-hydroxytryptamine (5-HT) receptor agonist, a 5-HT receptor antagonist, and a dopamine D receptor antagonist. Little is known about the effect of perospirone on pain transmission. Here, we explored whether perospirone attenuated neuropathic and inflammatory pain in the spinal cord. A chronic constriction injury to the sciatic nerve was induced in male Sprague-Dawley rats. We evaluated the effects of intrathecal administration of perospirone (10, 20, or 40 μg) on mechanical and cold hyperalgesia using the electronic von Frey and cold plate tests, respectively. Normal rats were assessed in terms of inflammatory nociception using the formalin test and for motor coordination employing the rotarod test. To define the mechanism underlying the action of perospirone, the effects of intrathecal pretreatment with the 5-HT receptor antagonist WAY-100635, the 5-HT receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-aminopropane (DOI), and the dopamine D receptor agonist sumanirole on perospirone action were examined using the electronic von Frey test and cold plate test. Perospirone dose-dependently alleviated mechanical and cold hyperalgesia, but not inflammatory nociception in the spinal cord, and affected motor coordination. WAY-100635 reversed the antihyperalgesic action of perospirone significantly, but neither DOI nor sumanirole exhibited such an effect. We conclude that perospirone attenuates mechanical and cold hyperalgesia principally via 5-HT receptor activation in the spinal cord, and the agent is a promising novel candidate for neuropathic pain relief.