The journal of pain : official journal of the American Pain Society
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Evidence suggests an important role for supraspinal gamma-aminobutyric acid (GABA) in conditioned fear and pain. Using dual probe microdialysis coupled to HPLC, we investigated alterations in extracellular levels of GABA simultaneously in the rat basolateral amygdala and dorsal periaqueductal gray during expression of conditioned fear, formalin-evoked nociception, and fear-conditioned analgesia. Re-exposure to a context previously paired with footshock significantly increased the duration of freezing and 22-kilohertz ultrasonic vocalization, and reduced formalin-evoked nociceptive behavior. Upon re-exposure to the context, GABA levels in the basolateral amygdala were significantly lower in fear-conditioned animals compared with non-fear-conditioned controls, irrespective of intraplantar formalin/saline injection. GABA levels in the dorsal periaqueductal gray were lower in rats receiving intraplantar injection of formalin, compared with saline-treated controls. GABA levels sampled were sensitive to nipecotic acid and calcium infusion. No specific fear-conditioned analgesia-related alterations in GABA efflux were observed in these regions despite the ability of rats undergoing dual probe microdialysis to express this important survival response. In conclusion, expression of contextually induced fear- and pain-related behavior are accompanied by suppression of GABA release in the basolateral amygdala and dorsal periaqueductal gray, respectively, compared with non-fear, non-pain controls. ⋯ This study investigates alterations in levels of the neurotransmitter GABA simultaneously in the rat amygdala and periaqueductal grey during expression of pain- and fear-related behavior and fear-induced analgesia. The results enhance our understanding of the role of this neurotransmitter in pain, memory of pain and control of pain during fear.
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Although there has been a rapid increase in Latino populations in the United States over the last 10 years, health research with Latino cultural groups is sorely lacking. In the area of pain-coping research, one consequence of the limited research is that very little is known about pain coping among Latinos. The purpose of this paper is to review the existing literature on pain coping in Latino populations, and to propose new directions for the future study of pain coping in Latino populations. This review is divided into 4 sections. In the first section, the challenges of defining Latino populations are discussed. In the second section, the current literature on pain coping in Latinos is reviewed. Third, we discuss the implications of existing findings for pain-coping assessment and pain treatment. Finally, we offer ideas for future research on pain coping in Latino populations. ⋯ In this review article, we identify gaps in our current understanding of pain coping in Latino cultural groups, and associated implications for pain assessment and treatment. We also highlight potential directions for future pain-coping research with Latino populations.
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Randomized Controlled Trial Clinical Trial
An investigation into the effects of frequency-modulated transcutaneous electrical nerve stimulation (TENS) on experimentally-induced pressure pain in healthy human participants.
Frequency-modulated transcutaneous electrical nerve stimulation (TENS) delivers currents that fluctuate between preset boundaries over a fixed period of time. This study compared the effects of constant-frequency TENS and frequency-modulated TENS on blunt pressure pain in healthy human volunteers. Thirty-six participants received constant-frequency TENS (80 pps), frequency-modulated TENS (20 to 100 pps), and placebo (no current) TENS at a strong nonpainful intensity in a randomized cross-over manner. Pain threshold was taken from the forearm using pressure algometry. There were no statistical differences between constant-frequency TENS and frequency-modulated TENS after 20 minutes (OR = 1.54; CI, 0.29, 8.23, P = 1.0). Both constant-frequency TENS and frequency-modulated TENS were superior to placebo TENS (OR = 59.5, P < .001 and OR = 38.5, P < .001, respectively). Frequency-modulated TENS does not influence hypoalgesia to any greater extent than constant-frequency TENS when currents generate a strong nonpainful paraesthesia at the site of pain. The finding that frequency-modulated TENS and constant-frequency TENS were superior to placebo TENS provides further evidence that a strong yet nonpainful TENS intensity is a prerequisite for hypoalgesia. ⋯ This study provides evidence that TENS, delivered at a strong nonpainful intensity, increases pain threshold to pressure algometry in healthy participants over and above that seen with placebo (no current) TENS. Frequency-modulated TENS does not increase hypoalgesia to any appreciable extent to that seen with constant-frequency TENS.
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Negative emotion has a variable effect on pain perception. This variability has been explained by the motivational priming hypothesis (MPH) which predicts that emotional stimuli generating low levels of arousal will facilitate pain, while stimuli generating high levels of arousal will inhibit pain. However, a study by Sneddon et al with rainbow trout discovers a relationship not found in the human literature, that fear-related behavior decreased in the presence of a nociceptive stimulus. The current experiment examined this possibility in humans. In Experiment 1, 30 healthy, female subjects with "at least a mild aversion to spiders" participated in 3 trials: 1 in which a Brazilian salmon pink tarantula was present; a second with the right hand immersed in a cold pressor; and a third with both the tarantula and the cold pressor present. Experiment 2 added distance as an extra variable to this methodology. In both experiments it was found that spider presence had no impact upon pain perception but spider fear was reduced by the cold pressor. There was no interaction between trial and either time or distance. These findings are novel in human subjects and not well accounted for by the MPH. We suggest that an explicitly evolutionary framework should be adopted, and that spider fear was reduced to facilitate escape from the more threatening cold-pressor experience. ⋯ This study examined the relationship between pain and fear. Subjects with an aversion to spiders sat next to a tarantula with their right hand in iced water. Subjects reported reduced fear but no change in pain. Consequently, the authors reevaluate the Motivational Priming Hypothesis and emphasize evolutionarily determined threat values.
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Although stress plays an important role in chronic widespread pain syndromes, such as fibromyalgia, the underlying mechanism has remained elusive. We have recently demonstrated, in a model of chronic widespread pain, that prolonged enhancement of immune mediator hyperalgesia, induced by unpredictable sound stress, requires a contribution of both the sympathoadrenal (epinephrine) and the hypothalamic-pituitary adrenal (corticosterone) neuroendocrine stress axes. Because this stress protocol produced sustained elevation of plasma epinephrine, in the current study we tested the hypothesis that the sympathoadrenal axis also plays a role in maintenance of symptoms in this model of chronic widespread pain. After establishment, adrenal medullectomy abolished the enhancement of epinephrine-induced cutaneous and muscle hyperalgesia. Administration of stress levels of epinephrine to adrenal medullectomized rats reconstituted the pain phenotype. These observations suggest that the sympathoadrenal stress axis plays a major role in the induction as well as maintenance of stress-induced enhancement of mechanical hyperalgesia, mediated by prolonged elevation of circulating epinephrine. ⋯ We present data showing mechanical hyperalgesia persisting for up to 28 days after exposure to sound stress, with evidence that the sympathoadrenal axis mediator epinephrine plays a major role. These findings could have clinical implications with regard to novel potential treatments for chronic widespread pain syndromes, such as fibromyalgia.