Differential Contribution of 5-HT₄, 5-HT₅, and 5-HT₆ Receptors to Acute Pruriceptive Processing Induced by...

The involvement of serotonin (5-HT) and/or noradrenaline in acute pruriceptive processing in the central nervous system (CNS) has been reported using antidepressants, such as milnacipran, a serotonin and noradrenaline reuptake inhibitor, and mirtazapine, a noradrenergic and specific serotonergic antidepressant; however, the roles of 5-HT receptor family in acute pruriceptive processing have not been fully elucidated in the CNS. In the present study, scratching behavior induced by chloroquine (CQ) was ameliorated by milnacipran or mirtazapine, and these effects were reversed by SB207266, a 5-HT₄ antagonist, or SB258585, a 5-HT₆ antagonist, but not by SB258585, a 5-HT₅ antagonist. Moreover, CQ-induced scratches were mitigated by intrathecal injection of 5-HT₄ agonists, such as BIMU8 and ML10302, and the 5-HT₆ agonist, WAY208466. Conversely, histamine-induced scratches were not affected by the 5-HT₄ agonists or a 5-HT₆ agonist. Similarly, the amelioration of histamine-induced scratches by these antidepressants was not reversed by the 5-HT₄, 5-HT₅, or 5-HT₆ receptor antagonist. Therefore, 5-HT is involved in the amelioration of CQ-induced scratches by milnacipran and mirtazapine, and 5-HT₄, 5-HT₅, and 5-HT₆ receptors play differential roles in acute pruriceptive processing after administration of CQ or histamine.