Collaborative action between noradrenergic and serotoninergic systems in peripheral antinociception in mice.

Noradrenaline (NA) and serotonin (5-HT) induce nociception and antinociception. This antagonistic effect can be explained by the dose and type of activated receptors. We investigated the existence of synergism between the noradrenergic and serotonergic systems during peripheral antinociception. The paw pressure test was performed in mice that had increased sensitivity by intraplantar injection of prostaglandin E ₂ (PGE ₂ ). Noradrenaline (80 ng) administered intraplantarly induced an antinociceptive effect, that was reversed by the administration of selective antagonists of serotoninergic receptors 5-HT _1B isamoltan, 5-HT _1D BRL15572, 5-HT _2A ketanserin, 5-HT ₃ ondansetron, but not by selective receptor antagonist 5-HT ₇ SB-269970. The administration of escitalopram, a serotonin reuptake inhibitor, potentiated the antinociceptive effect at a submaximal dose of NA. These results, indicate the existence of synergism between the noradrenergic and serotonergic systems in peripheral antinociception in mice.