Articles: hyperalgesia.
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Interruption of a continuous noxious heat by a relatively greater noxious heat evokes reductions in pain experience when the original noxious heat returns. The reduction is greater than that evoked by continuous delivery of noxious heat. This disproportionate reduction in pain experience, known as offset analgesia, is presumably mediated by a mechanism different to adaptation or habituation. ⋯ There was no attenuation effect for the unchanging stimuli delivered across the 3 days of testing but attenuation effects enhanced the offset analgesia resulting in a larger offset analgesia effect on days 2 and 3. It is possible that offset analgesia and attenuation are mediated by inter-related mechanisms. Further studies might investigate whether offset analgesia involves inhibitory structures such as the PAG-RVM.
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Antidepressant drugs act mainly by blocking the noradrenaline and/or serotonin uptake sites and require a chronic treatment. Tricyclic antidepressants are among the first line treatments clinically recommended against neuropathic pain. As observed against depression, a chronic treatment is required for a therapeutic effect. ⋯ For comparison, we tested the anticonvulsant gabapentin and showed that it alleviates neuropathic allodynia after 3 days of treatment. Naloxone had no effect on gabapentin therapeutic benefit, showing that antidepressants and anticonvulsants alleviate neuropathic allodynia through independent mechanisms. Our work provides a clinically relevant model to understand the mechanism by which chronic antidepressant treatment can alleviate neuropathic pain.
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Migraine patients may have cutaneous allodynia during attacks. In order to investigate if pain physiology changes in the preattack phase we estimated heat pain and cold pain detection threshold (HPT and CPT) on three different days in 41 migraine patients and 28 controls. ⋯ Subclinical preattack thermal pain hypersensitivity seems to be a feature of the process that leads to a migraine attack.
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Journal of neurotrauma · Nov 2008
Capsular ligament involvement in the development of mechanical hyperalgesia after facet joint loading: behavioral and inflammatory outcomes in a rodent model of pain.
Whiplash injury can produce pain in the neck, arm, and hand, and has been associated with inflammation. However, the relationship between inflammatory responses and pain symptoms remains unknown, hindering the development of appropriate therapeutics for whiplash symptoms. Two joint loading paradigms were used separately in an established rat model of painful cervical facet joint distraction to apply: (1) gross failure, and (2) subfailure distraction of the facet capsular ligament. ⋯ Cytokine mRNA levels in the spinal cord and DRG were also significantly elevated after facet ligament failure, but not after painful subfailure loading. Findings suggest that different joint loading scenarios produced varied inflammatory responses in the CNS. These data support existing clinical reports suggesting that therapeutic interventions directed at the facet capsule may be effective in treating this painful injury.
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Comparative Study
Pharmacological differences between static and dynamic allodynia in mice with herpetic or postherpetic pain.
In the present study, we investigated whether dynamic and static allodynia would be developed in the affected dermatome in murine models of herpetic pain and postherpetic neuralgia and pharmacologically characterized the allodynia. Inoculation with herpes simplex virus type-1 on the femur induced skin lesions in the dermatome including the plantar region of the hind paw from day 5 to day 21 after inoculation. Dynamic allodynia became apparent in the hind paw from day 3 to at least day 42. ⋯ Gabapentin (30 mg/kg, p.o.) markedly inhibited both static and dynamic allodynia. Developmental and pharmacological differences between static and dynamic allodynia suggest that independent mechanisms are responsible for dynamic and static allodynia. This murine model may be useful for the study of the mechanisms of dynamic allodynia of herpetic pain or postherpetic neuralgia and the development of new analgesics effective against the dynamic allodynia.