Pain
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Comparative Study
In vivo recruitment by painful stimuli of AMPA receptor subunits to the plasma membrane of spinal cord neurons.
The persistent increase in pain sensitivity observed after injury, known as hyperalgesia, depends on synaptic plasticity in the pain pathway, particularly in the spinal cord. Several potential mechanisms have been proposed, including post-synaptic exocytosis of the AMPA subclass of glutamate receptors (AMPA-R), which is known to play a critical role in synaptic plasticity in the hippocampus. AMPA-R trafficking has been described in spinal neurons in culture but it is unknown if it can also occur in spinal neurons in vivo, or if it can be induced by natural painful stimulation. ⋯ Brefeldin-A, an antibiotic that inhibits exocytosis of proteins, not only prevented GluR1 trafficking to the membrane but also inhibited referred hyperalgesia in capsaicin-treated mice. Our results show that delivery of GluR1 AMPA receptor subunits to the cell membrane through a CaMKII activity-dependent exocytotic regulated pathway contributes to the development of hyperalgesia after a painful stimulus. We conclude that AMPA-R trafficking contributes to the synaptic strengthening induced in the pain pathway by natural stimulation.
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Comparative Study
Increase in muscle nociceptive substances and anaerobic metabolism in patients with trapezius myalgia: microdialysis in rest and during exercise.
Local metabolic changes are suggested to be involved in muscle pain development in humans. Nineteen women with chronic work-related trapezius myalgia (TM) and 20 healthy female controls (CON) were studied during baseline rest, 20 min repetitive low-force exercise, and 120 min recovery. Interstitial serotonin (5-HT), glutamate, lactate, pyruvate, and blood flow were determined by microdialysis in the trapezius muscle. ⋯ In conclusion, patients with chronic work-related TM have increased levels of muscle 5-HT and glutamate that were correlated to pain intensity (r=0.55, P<0.001) and PPT (r=-0.47, P<0.001), respectively. In addition, TM was associated with increased anaerobic metabolism, whereas a normal rise in blood flow was seen with exercise. These findings indicate that peripheral nociceptive processes are active in work-related TM.
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Comparative Study
The effects of acute and chronic restraint stress on activation of ERK in the rostral ventromedial medulla and locus coeruleus.
Extracellular signal-regulated kinase (ERK) is a key molecule in numerous cellular and physiological processes in the CNS. Exposure to stressors causes substantial effects on the perception and response to pain. The rostral ventromedial medulla (RVM) and the locus coeruleus (LC) play crucial roles in descending pain modulation system. ⋯ Protein levels of tryptophan hydroxylase were significantly increased in the RVM region in the 3-week restraint rats. On the other hand, the chronic restraint stress significantly decreased p-ERK-IR in the LC [P<0.05]. These findings suggest that chronic restraint stress-induced activation of ERK in the RVM and the suppression in the LC may be involved in the modulation of the pain threshold by chronic stress.
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Comparative Study
Chronic orofacial pain among Korean elders: prevalence, and impact using the graded chronic pain scale.
The aims of this study were to investigate the prevalence of orofacial pain symptoms in the Korean elderly population, and to evaluate factors associated with orofacial pain and graded chronic pain. Of 4,342 Korean elders from the cohort of Korean National Interview Survey of Oral Health Status in 2000, telephone interviews were conducted on a stratified random sample of 1,032 people aged 55 years or older. Prevalence of five orofacial pain symptoms (jaw joint pain, face pain, toothache, oral sores, and burning mouth) in the past 6 months along with questions from the graded chronic pain scale were assessed by telephone using a structured questionnaire. ⋯ Subjects with joint pain, burning mouth or toothache pain were more likely to report high levels of a pain-related disability compared with subjects not reporting those symptoms. There were no age group differences in pain intensity, but the older age group reported a higher number of disability days because of their pain. Chronic orofacial pain is a substantial health problem in the elderly population.
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Comparative Study
Intracerebroventricular injection of phospholipases A2 inhibitors modulates allodynia after facial carrageenan injection in mice.
The present study was carried out, using inhibitors to secretory phospholipase A2 (sPLA2, 12-epi-scalaradial), cytosolic phospholipase A2 (cPLA2, AACOCF3), or calcium-independent phospholipase A2 (iPLA2, bromoenol lactone), to compare possible contributions of central nervous PLA2 isoforms to the development of allodynia after facial carrageenan injection in mice. C57BL/6J (B6) mice showed increased responses to facial stimulation using a von Frey hair (1 g force), at 8 h, 1 day, and 3 days after facial carrageenan injection. On the other hand, BALB/c mice did not show increased responses at any of the time points. ⋯ Since BALB/c mice did not show increased responses after facial carrageenan injection, the reduction in responses actually indicates that there is loss of normal sensitivity to von Frey hair stimulation after intracerebroventricular injection of each of these inhibitors, in this strain of mice. The effects of PLA2 inhibitors are unlikely to be due simply to inhibition of arachidonic acid generation, since intracerebroventricular injection of arachidonic acid also had an anti-nociceptive effect. The above results support an important role of central nervous PLA2s in neurotransmission and pain transmission.