The journal of pain : official journal of the American Pain Society
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The present study investigated the role of central metabotropic glutamate receptors (mGluRs) in interleukin-1beta (IL-1beta)-induced mechanical allodynia and mirror-image mechanical allodynia in the orofacial area. Experiments were carried out on male Sprague-Dawley rats weighing 230 to 280 g. After administration of 0.01, 0.1, 1, or 10 pg of IL-1beta into a subcutaneous area of the vibrissa pad, we examined the withdrawal behavioral responses produced by 10 successive trials of an air-puff ramp pressure applied ipsilaterally or contralaterally to the IL-1beta injection site. Subcutaneous injection of IL-1beta produced mechanical allodynia and mirror-image mechanical allodynia in the orofacial area. Intracisternal administration of CPCCOEt, a mGluR1 antagonist, or MPEP, a mGluR5 antagonist, reduced IL-1beta-induced mechanical allodynia and mirror-image mechanical allodynia. Intracisternal administration of APDC, a group II mGluR agonist, or L-AP4, a group III mGluR agonist, reduced both IL-1beta-induced mechanical allodynia and mirror-image mechanical allodynia. The antiallodynic effect, induced by APDC or L-AP4, was blocked by intracisternal pretreatment with LY341495, a group II mGluR antagonist, or CPPG, a group III mGluR antagonist. These results suggest that groups I, II, and III mGluRs differentially modulated IL-1beta-induced mechanical allodynia, as well as mirror-image mechanical allodynia, in the orofacial area. ⋯ Central group I mGluR antagonists and groups II and III mGluR agonists modulate IL-1beta-induced mechanical allodynia and mirror-image mechanical allodynia in the orofacial area. Therefore, the central application of group I mGluR antagonists or groups II and III mGluR agonists might be of therapeutic value in treating pain disorder.
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Multicenter Study
Catastrophizing and pain-contingent rest predict patient adjustment in men with chronic prostatitis/chronic pelvic pain syndrome.
Cognitive/behavioral and environmental variables are significant predictors of patient adjustment in chronic pain. Using a biopsychosocial template and selecting several pain-relevant constructs from physical, cognitive/behavioral, and environmental predictors, outcomes of pain and disability in chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) were explored. Men (n = 253) from a North American multi-institutional NIH-funded Chronic Prostatitis Cohort Study in 6 US and 1 Canadian centers participated in a survey examining pain and disability. Measures included demographics, urinary symptoms, depression, pain, disability, catastrophizing, control over pain, pain-contingent rest, social support, and solicitous responses from a significant other. Regressions showed that urinary symptoms (beta = .20), depression (beta = .24), and helplessness catastrophizing (beta = .29) predicted overall pain. Further, affective pain was predicted by depression (beta = .39) and helplessness catastrophizing (beta = .44), whereas sensory pain was predicted by urinary symptoms (beta = .25) and helplessness catastrophizing (beta = .37). With regard to disability, urinary symptoms (beta = .17), pain (beta = .21), and pain-contingent rest (beta = .33) were the predictors. These results suggest cognitive/behavioral variables (ie, catastrophizing, pain-contingent rest) may have significant impact on patient adjustment in CP/CPPS. Findings support the need for greater research of such pain-related variables in CP/CPPS. ⋯ This article explores predictors of patient adjustment in chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS). Cognitive/behavioral variables of catastrophizing and pain-contingent rest respectively predicted greater pain and disability. Catastrophic helplessness was a prominent pain predictor. These findings inform clinicians and researchers on several new variables in CP/CPPS outcomes and suggest future research.
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Prescription of opioids for nonmalignant musculoskeletal pain has increased substantially in recent years, but there is little information on the incidence of, or factors associated with, such prescription for work-related back pain. In a prospective cohort study (N = 1,067), we examined associations between worker sociodemographic and other characteristics and opioid prescription within six weeks of the first medical visit for workers' compensation claims for work loss due to back injury. We examined administrative, pharmacy, and worker-reported data. In bivariate logistic regression models, Hispanics were less likely than non-Hispanic whites to receive opioid prescriptions, and very high body mass index, daily tobacco use, greater pain and physical disability, pain radiating below the knee, injury severity categorizations (from medical records) of major sprain and radiculopathy, and worse mental health were associated with opioid prescription. Adjusting for demographics, pain intensity, and physical disability, opiate prescription was significantly associated with daily tobacco use, pain radiating below the knee, and injury severity categories (major sprain and radiculopathy). Knowledge of worker characteristics associated with early opioid prescription may be useful in future studies of the role of early pain treatment in influencing subsequent course of pain and disability among workers with back injuries. ⋯ Little is known about patient characteristics that may influence physicians' decisions concerning prescription of opioids for acute back pain. Not surprisingly, workers with more severe back injuries are more likely to be prescribed opioids, but reasons for prescription disparities based on ethnicity and tobacco use warrant further study.
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This high-resolution electroencephalography (EEG) study tested the hypothesis that the suppression of rolandic alpha power before predictable painful stimulation affects the subject's subsequent evaluation of pain intensity, as a reflection of the influence of expectancy processes on painful stimulus processing. High-resolution EEG data were recorded (126 channels) from 10 healthy adult volunteers during the expectancy of a painful CO(2)-laser stimulation at the right wrist. Surface laplacian estimation enhanced the EEG spatial information content over 6 scalp regions of interest (left frontal, right frontal, left central, right central, left parietal, and right parietal areas). Spectral power was computed for 3 alpha sub-bands with reference to the individual alpha frequency peak (about 5-7 Hz for alpha 1, 7-9 Hz for alpha 2, and 9-11 Hz for alpha 3). The suppression of the alpha power before the painful stimulation [as reflected by the event-related desynchronization (ERD)] indexed the anticipatory cortical processes. Results showed maximum (negative) correlations between the alpha 2 and alpha 3 ERD amplitude at the left central area and the subjective evaluation of pain intensity (P < .001). The stronger the anticipatory alpha 2 and alpha 3 ERD, the higher the subjective evaluation of pain intensity. For alpha 3, that correlation was confirmed even when the effect of habituation across the recording session was taken into account. These results suggest that the anticipatory suppression of the alpha rhythms over the contralateral primary sensorimotor cortex predicts subsequent subjects' evaluation of pain intensity, in line with its crucial role for the discrimination of that intensity. ⋯ This electroencephalographic study showed that anticipatory activation/deactivation of sensorimotor cortex roughly predicts subjective evaluation of pain. This motivates further investigation on possible implications for the understanding of central chronic pain. Chronic pain patients might exaggerate the anticipatory activation of sensorimotor cortex to negligible pain stimuli.
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Non-N-methyl-D-aspartate (non-NMDA) glutamate receptor antagonists modify multiple pain transmission pathways and are of particular interest in analgesic development because of their capacity to interfere with evoked pain. Evoked pain is a problem for postoperative patients and is characteristic of the plantar incision model for postoperative pain. The purpose of this study was to assess the efficacy of a non-NMDA receptor antagonist LY293558 on mechanical hyperalgesia after plantar incision in the rat. Parenteral, intrathecal, or intraplantar administration of LY293558 was tested against the mechanical hyperalgesia that characterizes the model. Sprague-Dawley rats were assigned to 1 of 3 groups. LY293558 or vehicle was administered intraperitoneally, intrathecally, or intraplantarly. The hind paw withdrawal threshold to punctate stimulation by using von Frey filaments and response frequency to a nonpunctate stimulus directly to the wound were measured. Motor tests after administration of LY293558 were also examined in rats that did not undergo incision. The greatest dose of parenterally administered LY293558 (34 micromol/kg) decreased the responses to mechanical stimuli after plantar incision. Rotorod performance was decreased at these same times. Intrathecal injection of LY293558 (0.5 and 2.0 nmol) produced inhibition of mechanical sensitivity and produced lower extremity motor side effects. Repeated intrathecal administration produced sustained anesthesia for 24 hours but had no analgesic effect the next day. Local administration did not decrease response after incision. LY293558 was most effective for evoked pain when administered intrathecally. ⋯ Control of evoked pain after surgery is inadequate but is linked to perioperative outcome. These data suggest that non-NMDA receptor antagonists like LY293558 will be most effective for evoked pain in postoperative patients if administered spinally.