Spinal dopaminergic D(1) and D(5) 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 D1-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 D1 and D5 receptor subtypes. Withdrawal and muscle pressure thresholds were assessed with von Frey filaments and the Randall-Selitto test, respectively. Expression of D1-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 D1-like receptor agonist SKF-38393 induced nociceptive hypersensitivity in naïve rats, whilst this effect was prevented by the D1-like receptor antagonist SCH-23390. Moreover, SCH-23390 induced a sex-dependent antiallodynic effect in reserpine-treated rats. Furthermore, transient silencing of D1 and D5 receptors significantly reduced reserpine-induced hypersensitivity in female rats. Reserpine slightly increased mRNA D5 receptor expression in dorsal spinal cord, but not in DRG. This work provides new insights about the involvement of the spinal dopaminergic D1/D5 receptors in reserpine-induced hypersensitivity in rats.

De la Luz-Cuellar YE ，Rodríguez-Palma EJ ，Franco-Enzástiga Ú ，Déciga-Campos M ，Mercado F ，Granados-Soto V ... -  《-》

Spinal dopaminergic D(1)-and D(2)-like receptors have a sex-dependent effect in an experimental model of fibromyalgia.

There is evidence about the importance of sex in pain. The purpose of this study was to investigate the effect of sex in the antiallodynic activity of spinal dopamine D1-and D2-like receptors in a model of fibromyalgia-type pain in rats. Reserpine induced the same extent of tactile allodynia in female and male rats. Intrathecal injection of SCH-23390 (3-30 nmol, D1-like receptor antagonist), pramipexole (0.15-15 nmol) or quinpirole (1-10 nmol D2-like receptor agonists) increased withdrawal threshold in reserpine-treated female rats. Those drugs induced a greater antiallodynic effect in female rats. Sex-difference was also observed in a nerve injury model. Ovariectomy abated the antiallodynic effect of SCH-23390 (30 nmol) in reserpine-treated rats, while systemic reconstitution of 17β-estradiol levels or intrathecal injection of estrogen receptor-α agonist protopanaxatriol in ovariectomized reserpine-treated females restored the antiallodynic effect of SCH-23390. Intrathecal administration of ICI-182,780 (estrogen receptor-α/β antagonist) or methyl-piperidino-pyrazole hydrate (estrogen receptor-α antagonist) abated 17β-estradiol-restored antiallodynic effect of SCH-23390 in rats. In contrast, ovariectomy slightly reduced the effect of pramipexole (15 nmol) or quinpirole (10 nmol) in reserpine-treated rats, whereas systemic reconstitution of 17β-estradiol levels did not modify the antiallodynic effect of both drugs. Combination 17β-estradiol/progesterone, but not 17β-estradiol nor progesterone alone, restored the antiallodynic effect of pramipexole and quinpirole in the rats. Mifepristone (progesterone receptor antagonist) abated 17β-estradiol + progesterone restoration of the antiallodynic effect of pramipexole and quinpirole. These data suggest that the antiallodynic effect of dopamine D1-and D2-like receptors in fibromyalgia-type pain depends on spinal 17β-estradiol/estrogen receptor-α and progesterone receptors, respectively.

De la Luz-Cuellar YE ，Coffeen U ，Mercado F ，Granados-Soto V ... -  《-》

Blockade of spinal α(5)-GABA(A) receptors differentially reduces reserpine-induced fibromyalgia-type pain in female rats.

The role of spinal α5 subunit-containing GABAA (α5-GABAA) receptors in chronic pain is controversial. The purpose of this study was to investigate the participation of spinal α5-GABAA receptors in the reserpine-induced pain model. Reserpine administration induced tactile allodynia and muscle hyperalgesia in female and male rats. Intrathecal injection of L-655,708 and TB 21007 (7 days after the last reserpine injection) decreased tactile allodynia and, at a lesser extent, muscle hyperalgesia in female rats. The effects of these drugs produced a lower antiallodynic and antihyperalgesic effect in male than in female rats. Contrariwise, these drugs produced tactile allodynia and muscle hyperalgesia in naïve rats and these effects were lower in naïve male than female rats. Intrathecal L-838,417 prevented or reversed L-655,708-induced antiallodynia in reserpine-treated female rats. Repeated treatment with α5-GABAA receptor small interfering RNA (siRNA), but not scramble siRNA, reduced reserpine-induced allodynia in female rats. Accordingly, α5-GABAA receptor siRNA induced nociceptive hypersensitivity in naïve female rats. Reserpine enhanced α5-GABAA receptors expression in spinal cord and dorsal root ganglia (DRG), while it increased CD11b (OX-42) and glial fibrillary acidic protein (GFAP) fluorescence intensity in the lumbar spinal cord. In contrast, reserpine diminished K+-Cl- co-transporter 2 (KCC2) protein in the lumbar spinal cord. Data suggest that spinal α5-GABAA receptors play a sex-dependent proallodynic effect in reserpine-treated rats. In contrast, these receptors have a sex-dependent antiallodynic role in naïve rats.

De la Luz-Cuellar YE ，Rodríguez-Palma EJ ，Franco-Enzástiga Ú ，Salinas-Abarca AB ，Delgado-Lezama R ，Granados-Soto V ... -  《-》

Kinins and their B(1) and B(2) receptors are involved in fibromyalgia-like pain symptoms in mice.

Fibromyalgia is a disease characterised as generalised chronic primary pain that causes functional disability and a reduction in patients' quality of life, without specific pathophysiology or appropriate treatment. Previous studies have shown that kinins and their B1 and B2 receptors contribute to chronic painful conditions. Thus, we investigated the involvement of kinins and their B1 and B2 receptors in a fibromyalgia-like pain model induced by reserpine in mice. Nociceptive parameters (mechanical allodynia, cold sensitivity and overt nociception) and behaviours of burrowing, thigmotaxis, and forced swimming were evaluated after reserpine administration in mice. The role of kinin B1 and B2 receptors was investigated using knockout mice or pharmacological antagonism. The protein expression of kinin B1 and B2 receptors and the levels of bradykinin and monoamines were measured in the sciatic nerve, spinal cord and cerebral cortex of the animals. Knockout mice for the kinin B1 and B2 receptor reduced reserpine-induced mechanical allodynia. Antagonism of B1 and B2 receptors also reduced mechanical allodynia, cold sensitivity and overt nociception reserpine-induced. Reserpine altered thigmotaxis, forced swimming and burrowing behaviour in the animals; with the latter being reversed by antagonism of kinin B1 receptor. Moreover, reserpine increased the protein expression of kinin B1 and B2 receptors and levels of kinin, as well as reduced the levels of monoamines in peripheral and central structures. Kinins and its B1 and B2 receptors are involved in fibromyalgia-like pain symptoms. B1 or B2 receptors might represent a potential target for the relief of fibromyalgia-like pain symptoms.

Brusco I ，Justino AB ，Silva CR ，Fischer S ，Cunha TM ，Scussel R ，Machado-de-Ávila RA ，Ferreira J ，Oliveira SM ... -  《-》

A Critical Role for Dopamine D5 Receptors in Pain Chronicity in Male Mice.

Dopaminergic modulation of spinal cord plasticity has long been recognized, but circuits affected by this system and the precise receptor subtypes involved in this modulation have not been defined. Dopaminergic modulation from the A11 nucleus of the hypothalamus contributes to plasticity in a model of chronic pain called hyperalgesic priming. Here we tested the hypothesis that the key receptor subtype mediating this effect is the D5 receptor (D5R). We find that a spinally directed lesion of dopaminergic neurons reverses hyperalgesic priming in both sexes and that a D1/D5 antagonist transiently inhibits neuropathic pain. We used mice lacking D5Rs (DRD5KO mice) to show that carrageenan, interleukin 6, as well as BDNF-induced hyperalgesia and priming are reduced specifically in male mice. These male DRD5KO mice also show reduced formalin pain responses and decreased heat pain. To characterize the subtypes of dorsal horn neurons engaged by dopamine signaling in the hyperalgesic priming model, we used c-fos labeling. We find that a mixed D1/D5 agonist given spinally to primed mice activates a subset of neurons in lamina III and IV of the dorsal horn that coexpress PAX2, a transcription factor for GABAergic interneurons. In line with this, we show that gabazine, a GABA-A receptor antagonist, is antihyperalgesic in primed mice exposed to spinal administration of a D1/D5 agonist. Therefore, the D5R, in males, and the D1R, in females, exert a powerful influence over spinal cord circuitry in pathological pain likely via modulation of deep dorsal horn GABAergic neurons.SIGNIFICANCE STATEMENT Pain is the most prominent reason why people seek medical attention, and chronic pain incidence worldwide has been estimated to be as high as 33%. This study provides new insight into how descending dopamine controls pathological pain states. Our work demonstrates that dopaminergic spinal projections are necessary for the maintenance of a chronic pain state in both sexes; however, D5 receptors seem to play a critical role in males whereas females rely more heavily on D1 receptors, an effect that could be explained by sexual dimorphisms in receptor expression levels. Collectively, our work provides new insights into how the dopaminergic system interacts with spinal circuits to promote pain plasticity.

Megat S ，Shiers S ，Moy JK ，Barragan-Iglesias P ，Pradhan G ，Seal RP ，Dussor G ，Price TJ ... -  《-》