Spinal dopaminergic D and D receptors contribute to reserpine-induced fibromyalgia-like pain in rats.

Fibromyalgia is a complex pain syndrome without a precise etiology. Reduced monoamines levels in serum and cerebrospinal fluid in fibromyalgia patients has been reported and could lead to a dysfunction of descending pain modulatory system producing the painful syndrome. This study evaluated the role of D-like dopamine receptors in the reserpine-induced fibromyalgia-like pain model in female Wistar rats. Reserpine-treated animals were intrathecally injected with different dopamine receptors agonists and antagonists, and small interfering RNAs (siRNAs) against D and D receptor subtypes. Withdrawal and muscle pressure thresholds were assessed with von Frey filaments and the Randall-Selitto test, respectively. Expression of D-like receptors in lumbar spinal cord and dorsal root ganglion was determined using real time polymerase chain reaction (qPCR). Reserpine induced tactile allodynia and muscle hyperalgesia. Intrathecal dopamine and D-like receptor agonist SKF-38393 induced nociceptive hypersensitivity in naïve rats, whilst this effect was prevented by the D-like receptor antagonist SCH-23390. Moreover, SCH-23390 induced a sex-dependent antiallodynic effect in reserpine-treated rats. Furthermore, transient silencing of D and D receptors significantly reduced reserpine-induced hypersensitivity in female rats. Reserpine slightly increased mRNA D receptor expression in dorsal spinal cord, but not in DRG. This work provides new insights about the involvement of the spinal dopaminergic D/D receptors in reserpine-induced hypersensitivity in rats.