Pain
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Chronic migraine is a disabling condition that affects hundreds of millions of individuals worldwide. The development of novel migraine treatments has been slow, in part as a result of a lack of predicative animal models. We have developed a new model of chronic migraine involving the use of nitroglycerin (NTG), a known migraine trigger in humans. ⋯ NTG-evoked hyperalgesia was exacerbated by the phosphodiesterase 5 inhibitor sildenafil, also a human migraine trigger, consistent with nitric oxide as a primary mediator of this hyperalgesia. The acute but not the chronic basal hyperalgesia was significantly reduced by the acute migraine therapy sumatriptan, whereas both the acute and chronic hyperalgesia was significantly attenuated by the migraine preventive therapy topiramate. Chronic NTG-induced hyperalgesia is a mouse model that may be useful for the study of mechanisms underlying progression of migraine from an episodic to a chronic disorder, and for the identification and characterization of novel acute and preventive migraine therapies.
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Bone cancer pain is a common and disruptive symptom in cancer patients. In cancer pain animal models, massive reactive astrogliosis in the dorsal horn of the spinal cord has been reported. Because astrocytes may behave as driving partners for pathological pain, we investigated the temporal development of pain behavior and reactive astrogliosis in a rat bone cancer pain model induced by injecting MRMT-1 rat mammary gland carcinoma cells into the tibia. ⋯ In contrast, all these parameters were increased in the dorsal horn of rats 2weeks after sciatic nerve ligation. This suggests that in some cases, bone cancer pain may not be correlated with spinal overexpression of reactive glia markers, whereas neuropathic pain is. Glia may thus play different roles in the development and maintenance of chronic pain in these 2 situations.
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Clinical Trial
A CRPS-IgG-Transfer-Trauma Model Reproducing Inflammatory and Positive Sensory Signs associated with Complex Regional Pain Syndrome.
The aetiology of complex regional pain syndrome (CRPS), a highly painful, usually post-traumatic condition affecting the limbs, is unknown, but recent results have suggested an autoimmune contribution. To confirm a role for pathogenic autoantibodies, we established a passive-transfer trauma model. Prior to undergoing incision of hind limb plantar skin and muscle, mice were injected either with serum IgG obtained from chronic CRPS patients or matched healthy volunteers, or with saline. ⋯ Plantar incision induced a remarkable elevation of substance P immunoreactivity on day 8, which was significantly increased by CRPS-IgG. In this IgG-transfer-trauma model for CRPS, serum IgG from chronic CRPS patients induced clinical and laboratory features resembling the human disease. These results support the hypothesis that autoantibodies may contribute to the pathophysiology of CRPS, and that autoantibody-removing therapies may be effective treatments for long-standing CRPS.
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The persistence of pain after surgery increases the recovery interval from surgery to a normal quality of life. AYX1 is a DNA-decoy drug candidate designed to prevent post-surgical pain following a single intrathecal injection. Tissue injury causes a transient activation of the transcription factor EGR1 in the dorsal root ganglia-dorsal horn network, which then triggers changes in gene expression that induce neuronal hypersensitivity. ⋯ Administered in the peri-operative period, AYX1 dose dependently prevents mechanical hypersensitivity in models of acute incisional (plantar), inflammatory (CFA), and chronic neuropathic pain (SNI) in rats. Furthermore, in a knee surgery model evaluating functional measures of postoperative pain, AYX1 improved weight-bearing incapacitance and spontaneous rearing compared to control. These data illustrate the potential clinical therapeutic benefits of AYX1 for preventing the transition of acute to chronic post-surgical pain.
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Neuropathic pain (NP) is not easy to understand for those with the diagnosis. Even in specialist medical services, explanation may not be given or may not be integrated with patients' existing beliefs about their conditions. We were curious about how people with NP conceptualised the problem. ⋯ Overall, a biopsychosocial model of pain was only weakly represented, and no integrated model of pain emerged across the four different accounts. There was little reference to NP having been explained when the diagnosis was made. This study highlights the need for more accessible explanations of NP within and outside medical services if people with NP are to use their understanding of NP to help them manage their pain and reduce its impact on their lives.