European journal of pain : EJP
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The analgesic effect of nitrous oxide (N(2)O) is thought to depend on noradrenaline release in the spinal cord following activation of descending inhibitory neurons. In addition to this indirect facilitation of inhibition in the spinal cord, we previously showed direct inhibition of glutamate receptors in dorsal horn neurons by N(2)O. Since general anesthetics could possibly affect excitatory and/or inhibitory components of synaptic transmission, we sought to evaluate the direct effect of N(2)O on inhibitory transmission in spinal cord neurons. ⋯ N(2)O did not affect the amplitude, frequency or decay time probability distribution of either GABA or glycine receptor-mediated miniature postsynaptic currents. We further sought to determine the effect of N(2)O on focal stimulation-evoked synaptic currents mediated by GABA and glycine receptors, and found no effect in the majority of neurons. These and other findings suggest that N(2)O has a discrete action in the spinal cord, distinct from the effects of the volatile anesthetics, consisting of inhibition of excitation in SG neurons through an action on ionotropic glutamatergic receptors and potentiation of inhibition through the descending noradrenergic system.
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Many patients with multiple sclerosis (MS) develop central neuropathic pain (CP). In the present study somatosensory abnormalities have been analysed in detail in 62 patients with MS and CP (42 women, 20 men; mean age 52 years) and in a control group of 10 women and 6 men (mean age 47 years) with MS and sensory symptoms, but without pain. Assessment included clinical testing and quantitative methods (QST) for the measurement of perception thresholds for touch, vibration, and temperatures. ⋯ Comparisons between painful and non-painful regions showed both the absolute threshold values and the index values to be significantly more abnormal, in the CP regions, for warmth (p<0.001), cold (p<0.05), difference limen (innoxious warmth and cold, p<0.01), cold pain (p<0.01) and heat pain/cold pain combined (p<0.001). Also the comparisons between regions with central pain and regions with sensory symptoms in the controls showed significantly more abnormal thresholds in the CP patients for warmth (p<0.05), cold (p<0.01), difference limen (innoxious warmth and cold, p<0.01) and heat pain/cold pain combined (p<0.001). The results support the general hypothesis that only patients who have lesions affecting the spinothalamo-cortical pathways run the risk of developing central pain.
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In our previous studies, psychological stress was shown to enhance operant escape responding of male and female rats. The stressors that produced hyperalgesia were physical restraint and social defeat. Nociceptive input also elicits stress reactions, generating the prediction that pain would facilitate pain under certain circumstances. ⋯ Similarly, escape from cold (10 degrees C) was enhanced when preceded by escapable 44.5 degrees C stimulation. Thus, prior nociceptive stimulation enhanced escape from aversive thermal stimulation. Facilitation of pain by a preceding pain experience is consistent with stress-induced hyperalgesia and contrasts with other models of pain inhibition by concurrent nociceptive stimulation.
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Randomized Controlled Trial
Long-term follow-up of tailored behavioural treatment and exercise based physical therapy in persistent musculoskeletal pain: A randomized controlled trial in primary care.
This study examined long-term effects of a tailored behavioural treatment protocol (TBT), as compared with an exercise based physical therapy protocol (EBT). One-hundred and twenty-two patients who, due to persistent musculoskeletal pain, consulted physical therapists in primary care were originally randomized to either of the two conditions. Follow-up assessments two-year post-treatment were completed by 65 participants. ⋯ Fear of movement/(re)injury increased in the EBT-group, and EBT participants reported higher fear of movement/(re)injury two years post-treatment compared to TBT. The study supports tailoring of treatments in concordance with patients' needs and preferences of activity goals and functional behavioural analyses including predictors of pain-related disability, for successful immediate outcomes and their maintenance in the long run. Exercise-based treatments resulted in somewhat smaller immediate treatment effects but had similar maintenance of effects over the 2-year follow-up period.
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Patients with chronic low back pain (CLBP) often report a disabling decrease in their activity level due to pain. The nature of the association between disability, activity, and pain over time is however, unclear. An intriguing issue here is whether a high level of pain-related disability is associated with a low activity level or are changes in the level of activity over time pain provoking and thus more disabling? The objectives of this study were to investigate associations between disability, pain intensity, pain-related fear, and characteristics of physical activity in patients with CLBP. ⋯ To explain the level of disability regression analyses were performed with disability as dependent variable and pain intensity, pain-related fear, and consecutively the level of physical activity in daily life and fluctuations in physical activity as independent variables. Results, based on 34 patients, showed that activity fluctuations (beta=0.373, p<0.05) rather than the mean activity level over time (beta=-0.052, ns) contributed significantly in explaining disability. The results are discussed in the light of current theories, previous research, and clinical implications.