The involvement of dopamine in nociception: the role of D 1 and D 2 receptors in the dorsolateral striatum

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Determination of the neuroanatomical and neurochemical factors that contribute to nociception is an essential element in the study and treatment of pain. Several lines of evidence have implicated nuclei and neurotransmitters within the basal ganglia in nociception. For example, previous studies have shown that dopamine receptors in the striatum are involved in acute nociception, however, it remains to be determined if dopamine receptors in the dorsolateral striatum are involved in persistent nociception. The purpose of the present study was therefore to determine whether activation or antagonism of dopamine receptors in the dorsolateral striatum influences the nociceptive responses of rats in the formalin test, a model of persistent pain. It was found that micro-injection of the non-selective dopamine antagonist haloperidol into the dorsolateral striatum increases formalin-induced nociception whereas injection of the non-selective dopamine agonist apomorphine reduces formalin-induced nociception. Injection of the D 1 antagonist SCH23390 or the D 1 agonist SKF38393 does not affect formalin-induced nociception. In contrast, injection of the D 2 antagonist eticlopride enhances formalin-induced nociception, whereas injection of the D 2 agonist quinpirole reduces formalin-induced nociception. These results provide additional evidence that dopamine receptors in the striatum are involved in nociception. Furthermore, this study strongly suggests that D 2, but not D 1, dopamine receptors in the dorsolateral striatum are involved in modulation of persistent nociception.