Pain
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Comparative Study Clinical Trial
Sensory responses to injection and punctate application of capsaicin and histamine to the skin.
A punctate, cutaneous application of capsaicin or histamine by means of a cowhage spicule elicits itch accompanied by pricking/stinging, burning, and typically, one or more areas of dysesthesia (alloknesis, hyperalgesia, hyperknesis). When applied over a wider and deeper area of skin by means of intradermal injection, histamine evokes the same sensory effects, but capsaicin evokes pain and hyperalgesia with allodynia instead of alloknesis. To examine the sensory effects of the spatial spread, depth, and amount of capsaicin and histamine, we applied different amounts of capsaicin or histamine by intradermal injection or by single vs multiple spicules within a circular cutaneous region of ~5 mm. ⋯ However, there was little or no itch; and allodynia replaced alloknesis. Yet, hyperalgesia was typically accompanied by hyperknesis. We conclude that the pruritic sensory responses produced by capsaicin/histamine spicules and histamine injections may be due to activation of common nerve fibers, possibly different from those mediating the flare, and that capsaicin injections may activate additional fibers whose effects mask the sensory effects of fibers mediating itch and alloknesis but not hyperknesis.
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Back pain is one of the most common causes of disability in industrialized nations. Despite this, the variables that contribute to disability are not well understood and optimal measurement strategies of disability have not yet been determined. The present study sought to comprehensively assess the strongest predictors of physical activity as a proxy for disability. ⋯ Subsequent analyses showed that pain sensitivity, fear avoidance, and solicitous spousal responses account for a significant amount of the variance in physical activity. These findings suggest that external sources of reinforcement or punishment may serve to influence physical behavior beyond that of internal cues such as fear avoidance or pain. Implications for treatment are discussed, including the potential benefits of specifically incorporating the patient's sources of operant reinforcement or punishment into treatment.
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Women with metastatic breast cancer (MBC) rely on their partners for emotional and practical support. They also experience significant pain and depression, which can trigger maladaptive pain behaviors (eg, distorted ambulation). The biopsychosocial model of pain posits that partner solicitous responses can reinforce pain behaviors, whereas punishing or distracting responses can minimize their occurrence. ⋯ Specifically, punishing responses were associated with more pain behaviors for patients with low levels of pain and fewer pain behaviors for patients with higher levels of pain (effect size r=.18). These findings provide partial support for the biopsychosocial model of pain but also clarify and extend it in the cancer context. Future pain management programs in MBC may benefit from addressing both partners' depression levels and teaching partners to engage in fewer punishing responses when the patient is experiencing low levels of pain.
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Chronic pain in adults has been associated with early-life stress. To examine the pronociceptive effect of early-life stress, we evaluated cutaneous and muscle nociception and activity in muscle nociceptors in an animal model of neonatal stress, limited bedding, in the rat. In this neonatal limited bedding (NLB) model, litters are exposed to limited bedding between postnatal days 2 and 9, and controls to standard bedding. ⋯ Furthermore, administration of prostaglandin E(2) in skin as well as muscle produced markedly prolonged hyperalgesia, an effect prevented by spinal intrathecal injection of oligodeoxynucleotide antisense to protein kinase Cε (PKCε), a second messenger in nociceptors that has been implicated in the induction and maintenance of chronic pain. In electrophysiological studies, mechanical threshold of muscle nociceptors was reduced by ~31% and conduction velocity significantly increased (~28%). These findings indicate that neonatal stress induces a persistent hyperalgesia and nociceptor sensitization manifest in the adult and that the second messenger PKCε may be a target against which therapies might be directed to treat a chronic pain syndrome that is associated with early-life traumatic stress.