Pronociceptive role of spinal Cav2.3 (R-type) calcium channels in a mouse model of postoperative pain.

BACKGROUND: More than 80% of patients may experience acute pain after a surgical procedure, and this is often refractory to pharmacological intervention. The identification of new targets to treat postoperative pain is necessary. There is an association of polymorphisms in the Cav2.3 gene with postoperative pain and opioid consumption. Our study aimed to identify Cav2.3 as a potential target to treat postoperative pain and to reduce opioid-related side effects. EXPERIMENTAL APPROACH: A plantar incision model was established in adult male and female C57BL/6 mice. Cav2.3 expression was detected by qPCR and suppressed by siRNA treatment. The antinociceptive efficacy and safety of a Cav2.3 blocker-alone or together with morphine-was also assessed after surgery. KEY RESULTS: Paw incision in female and male mice caused acute nociception and increased Cav2.3 mRNA expression in the spinal cord but not in the incised tissue. Intrathecal treatment with siRNA against Cav2.3, but not with a scrambled siRNA, prevented the development of surgery-induced nociception in both male and female mice, with female mice experiencing long-lasting effects. High doses of i.t. SNX-482, a Cav2.3 channel blocker, or morphine injected alone, reversed postoperative nociception but also induced side effects. A combination of lower doses of morphine and SNX-482 mediated a long-lasting reversal of postsurgical pain in female and male mice. CONCLUSION: Our results demonstrate that Cav2.3 has a pronociceptive role in the induction of postoperative pain, indicating that it is a potential target for the development of therapeutic approaches for the treatment of postoperative pain.

Topical application of a TRPA1 antagonist reduced nociception and inflammation in a model of traumatic muscle injury in rats.

Musculoskeletal pain is a widely experienced public healthcare issue, especially after traumatic muscle injury. Besides, it is a common cause of disability, but this pain remains poorly managed. However, the pathophysiology of traumatic muscle injury-associated pain and inflammation has not been fully elucidated. In this regard, the transient receptor potential ankyrin 1 (TRPA1) has been studied in inflammatory and painful conditions. Thus, this study aimed to evaluate the antinociceptive and anti-inflammatory effect of the topical application of a TRPA1 antagonist in a model of traumatic muscle injury in rats. The mechanical trauma model was developed by a single blunt trauma impact on the right gastrocnemius muscle of Wistar male rats (250-350 g). The animals were divided into four groups (Sham/Vehicle; Sham/HC-030031 0.05%; Injury/Vehicle, and Injury/HC-030031 0.05%) and topically treated with a Lanette® N cream base containing a TRPA1 antagonist (HC-030031, 0.05%; 200 mg/muscle) or vehicle (Lanette® N cream base; 200 mg/muscle), which was applied at 2, 6, 12, 24, and 46 h after muscle injury. Furthermore, we evaluated the contribution of the TRPA1 channel on nociceptive, inflammatory, and oxidative parameters. The topical application of TRPA1 antagonist reduced biomarkers of muscle injury (lactate/glucose ratio), spontaneous nociception (rat grimace scale), inflammatory (inflammatory cell infiltration, cytokine levels, myeloperoxidase, and N-acetyl-ß-D-glucosaminidase activities) and oxidative (nitrite levels and dichlorofluorescein fluorescence) parameters, and mRNA Trpa1 levels in the muscle tissue. Thus, these results demonstrate that TRPA1 may be a promising anti-inflammatory and antinociceptive target in treating muscle pain after traumatic muscle injury.

Critical Pronociceptive Role of Family 2 Voltage-Gated Calcium Channels in a Novel Mouse Model of HIV-Associated Sensory Neuropathy.

Some people living with HIV present painful sensory neuropathy (HIV-SN) that is pharmacoresistant, sex-associated, and a major source of morbidity. Since the specific mechanisms underlying HIV-SN are not well understood, the aim of our study was to characterize a novel model of painful HIV-SN by combining the HIV-1 gp120 protein and the antiretroviral stavudine (d4T) in mice and to investigate the pronociceptive role of the family 2 voltage-gated calcium channel (VGCC) α1 subunit (Cav2.X channels) in such a model. HIV-SN was induced in male and female C57BL/6 mice by administration of gp120 and/or d4T and detected by a battery of behavior tests and by immunohistochemistry. The role of Cav2.X channels was assessed by the treatment with selective blockers and agonists as well as by mRNA detection. Repeated administration with gp120 and/or d4T produced long-lasting touch-evoked painful-like behaviors (starting at 6 days, reaching a maximum on day 13, and lasting up to 28 days after treatment started), with a greater intensity in female mice treated with the combination of gp120 + d4T. Moreover, gp120 + d4T treatment reduced the intraepidermal nerve fibers and well-being of female mice, without altering other behaviors. Mechanistically, gp120 + d4T treatment induced Cav2.1, 2.2, and 2.3 transcriptional increases in the dorsal root ganglion and the Cav2.X agonist-induced nociception. Accordingly, intrathecal selective Cav2.2 blockade presented longer and better efficacy in reversing the hyperalgesia induced by gp120 + d4T treatment compared with Cav2.1 or Cav2.3, but also presented the worst safety (inducing side effects at effective doses). We conclude that the family 2 calcium channels (Cav2.X) exert a critical pronociceptive role in a novel mouse model of HIV-SN.

Unpredictable Sound Stress Model Causes Migraine-Like Behaviors in Mice With Sexual Dimorphism.

Migraine represents one of the major causes of disability worldwide and is more prevalent in women; it is also related to anxiety symptoms. Stress, such as sound stress, is a frequently reported trigger in migraine patients, but the underlying mechanisms are not fully understood. However, it is known that patients with migraine have higher levels of plasma inflammatory cytokines and calcitonin gene-related peptide (CGRP). Stress mediated by unpredictable sound is already used as a model of painful sensitization, but migraine-like behaviors and sexual dimorphism have not yet been evaluated. This study characterized nociception and anxiety-related symptoms after the induction of sound stress in mice. C57BL/6 mice (20-30 g) were exposed to unpredictable sound stress for 3 days, nonconsecutive days. We observed enhanced plasma corticosterone levels on day 1 after stress induction. First, 7 days after the last stress session, mice developed hind paw and periorbital mechanical allodynia, grimacing pain behavior, anxiety-like symptoms, and reduced exploratory behavior. The nociceptive and behavioral alterations detected in this model were mostly shown in female stressed mice at day 7 post-stress. In addition, on day 7 post-stress nociception, these behaviors were consistently abolished by the CGRP receptor antagonist olcegepant (BIBN4096BS, 100 mg/kg by intraperitoneal route) in female and male stressed mice. We also demonstrated an increase in interleukine-6 (IL-6), tumor necrosis factor (TNF-α), and CGRP levels in stressed mice plasma, with female mice showing higher levels compared to male mice. This stress paradigm allows further preclinical investigation of mechanisms contributing to migraine-inducing pain.