Pain
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Comparative Study
Neuropathic pain: are there distinct subtypes depending on the aetiology or anatomical lesion?
Neuropathic pain can be caused by a variety of nerve lesions and it is unsettled whether it should be categorised into distinct clinical subtypes depending on aetiology or type of nerve lesion or individualised as a specific group, based on common symptomatology across aetiologies. In this study, we used a multivariate statistical method (multiple correspondence analyses) to investigate associations between neuropathic positive symptoms (assessed with a specific questionnaire, the Neuropathic Pain Symptom Inventory [NPSI]) and aetiologies, types of nerve lesion and pain localisations. We also examined the internal structure of the NPSI and its relevance to evaluation of symptoms of evoked pains by exploring their relationships with clinician-based quantified measures of allodynia and hyperalgesia. ⋯ Multiple correspondence analyses indicated few associations between symptoms (or dimensions) and aetiologies, types of lesions, or pain localisations. Exceptions included idiopathic trigeminal neuralgia and postherpetic neuralgia. We found that there are more similarities than differences in the neuropathic positive symptoms associated with a large variety of peripheral and central lesions, providing rationale for subgrouping aetiologically diverse neuropathic patients into a specific multidimensional category for therapeutic management.
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Comparative Study
Sensitization of primary afferents to mechanical and heat stimuli after incision in a novel in vitro mouse glabrous skin-nerve preparation.
In this study, we recorded activity from afferent fibers innervating the mouse plantar skin, the same region evaluated in pain behavior experiments. We compared responses of afferents from incised and unincised hind paw skin. The plantar skin together with attached medial and lateral plantar nerves was dissected until they could be completely removed intact and placed in an organ bath chamber continuously perfused with oxygenated Kreb's solution with the temperature maintained at 32 degrees C. ⋯ Few fibers were excited by cooling. Heat sensitization of primary afferents was more prominent when activities of unclassified afferents are included. The preparation allows us to study afferent function of the same tissue that is examined for in vivo pain behavior assays in mice.
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Comparative Study
Endogenous kappa-opioid receptor systems inhibit hyperalgesia associated with localized peripheral inflammation.
Peripheral inflammation evokes functional and biochemical changes in the periphery and spinal cord which result in central sensitization and hypersensitivity. Inhibitory control systems from the rostral ventromedial medulla (RVM) are also activated. The present study investigates whether endogenous kappa-opioid receptor (KOPr) systems contribute to these neuroadaptations. ⋯ These data demonstrate a previously unrecognized role of endogenous KOPr systems in inhibiting hyperalgesia during inflammation. Furthermore, they demonstrate that decreased KOPr activity in either the spinal cord or RVM not only enhances mechanical and thermal hyperalgesia of the inflamed limb but also leads to an unmasking of mechanical hyperalgesia at a site remote from inflammation. The differential effects of KOPr antagonism on mechanical versus thermal thresholds for the non-inflamed paw support the notion that distinct neuroanatomical or neurochemical mechanisms modulate the processing of thermal versus mechanical stimuli.
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Surgical and medical procedures, mainly those associated with nerve injuries, may lead to chronic persistent pain. Currently, one cannot predict which patients undergoing such procedures are 'at risk' to develop chronic pain. We hypothesized that the endogenous analgesia system is key to determining the pattern of handling noxious events, and therefore testing diffuse noxious inhibitory control (DNIC) will predict susceptibility to develop chronic post-thoracotomy pain (CPTP). ⋯ For prediction of acute post-operative pain intensity, DNIC efficiency was not found significant. Effectiveness of the endogenous analgesia system obtained at a pain-free state, therefore, seems to reflect the individual's ability to tackle noxious events, identifying patients 'at risk' to develop post-intervention chronic pain. Applying this diagnostic approach before procedures that might generate pain may allow individually tailored pain prevention and management, which may substantially reduce suffering.