Role of 5-HT3 receptors in the mechanisms of central pain syndrome

Electrophysiological and behavioral studies showed that spinal 5-HT₃ receptors are involved in the regulation of pain sensitivity in rats. Intrathecal administration of the 5-HT₃ receptor antagonist tropine (200 g) produced allodynia, reduced the threshold, decreased the latency, and increased the number of spikes in the late component of the nociceptive flexion reflex. Intrathecal administration of 5-HT₃ receptor agonist quipazine (200 mg) abolished nociceptive flexion reflex and alleviated spinal pain syndrome produced by impairment of GABAergic inhibition in the lumbar spinal segments. Our results indicate that spinal 5-HT₃ receptors are involved in the modulation of pain sensitivity: activation of these receptors inhibits nociceptive reactions, while blockade of 5-HT₃ receptors potentiates the nociceptive response via modulation of excitability of GABAergic interneurons.