Parental history of chronic pain may be associated with impairments in endogenous opioid analgesic systems

Twenty-year Outcomes of a Pediatric Chronic Abdominal Pain Cohort: Early Adulthood Health Status and Offspring Physical and Behavioral Health

Chronic abdominal pain (CAP) represents a common pediatric primary pain disorder that can have long-term effects on physical and mental health into adulthood. Pediatric CAP and Control cohorts recruited in childhood (∼11 years old, T1) and then assessed in emerging adulthood (∼20 years old, T2) were evaluated again for health outcomes in early adulthood (∼30 years old, T3) for the current study. Further, the study evaluated the mental and physical health of offspring of participants who had become parents. Participants who agreed to enroll at T3 (CAP: n = 90, Control: n = 55) completed measures regarding current health, health-related quality of life (HRQoL), and their child's health when applicable. Results indicated close to 20% of the CAP cohort reported recurrent CAP across all 3 timepoints. Participants with current CAP reported poorer HRQoL compared to participants with remitted CAP who reported poorer HRQoL compared to Control participants. The CAP cohort reported higher health-related anxiety compared to the Control cohort regardless of current pain status. CAP compared to Control participants reported greater emotional problems and fewer conduct problems in their children. Longitudinal studies are needed to assess the developmental course of pediatric chronic pain and intergenerational pathways of risk and resilience. Perspective: This article evaluates patterns of chronic abdominal pain from childhood into early adulthood. Patients with pediatric chronic abdominal pain continue to present with health-related anxiety in adulthood and report greater emotional problems in offspring.

The Emerging Role of Quercetin in the Treatment of Chronic Pain

Despite much research efforts being devoted to designing alternative pharmacological interventions, chronic pain remains to be an unresolved clinical problem. Quercetin, a compound that belongs to the flavonoids family, is abundantly found in fruits and vegetables. Emerging evidence indicates that quercetin possesses anti-nociceptive effects in different rodent models of chronic pain, including inflammatory pain, neuropathic pain and cancer pain. In this review, we summarize the mechanisms underlying the analgesic effect of quercetin in preclinical studies. These studies showed that quercetin exerts potent analgesic effects against chronic pain via suppressing neuroinflammation and oxidative stress as well as modulation of synaptic plasticity, GABAergic system, and opioidergic system. Considering that the safety of quercetin is well established, it has great potential for clinical use in pain treatment.

Greater Conditioned Pain Modulation Is Associated With Enhanced Morphine Analgesia in Healthy Individuals and Patients With Chronic Low Back Pain

OBJECTIVES

Conditioned pain modulation (CPM) protocols index magnitude of descending pain inhibition. This study evaluated whether the degree of CPM, controlling for CPM expectancy confounds, was associated with analgesic and subjective responses to morphine and whether chronic pain status or sex moderated these effects.

MATERIALS AND METHODS

Participants included 92 individuals with chronic low back pain and 99 healthy controls, none using daily opioid analgesics. In a cross-over design, participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo before undergoing evoked pain assessment. In each session, participants engaged in ischemic forearm and heat pain tasks, and a CPM protocol combining ischemic pain (conditioning stimulus) and heat pain (test stimulus). Placebo-controlled morphine outcomes were derived as differences in pain and subjective effects across drug conditions.

RESULTS

In hierarchical regressions controlling for CPM expectancies, greater placebo-condition CPM was associated with less subjective morphine unpleasantness (P=0.001) and greater morphine analgesia (P's<0.05) on both the ischemic pain task (Visual Analog Scale Pain Intensity and Unpleasantness) and heat pain task (Visual Analog Scale Pain Intensity, McGill Pain Questionnaire-Sensory, and Present Pain Intensity subscales). There was no moderation by sex or chronic low back pain status, except for the ischemic Present Pain Intensity outcome for which a significant 2-way interaction (P<0.05) was noted, with men showing a stronger positive relationship between CPM and morphine analgesia than women.

DISCUSSION

Results suggest that CPM might predict analgesic and subjective responses to opioid administration. Further evaluation of CPM as an element of precision pain medicine algorithms may be warranted.

The association between endogenous opioid function and morphine responsiveness: a moderating role for endocannabinoids

We sought to replicate previous findings that low endogenous opioid (EO) function predicts greater morphine analgesia and extended these findings by examining whether circulating endocannabinoids and related lipids moderate EO-related predictive effects. Individuals with chronic low-back pain (n = 46) provided blood samples for endocannabinoid analyses, then underwent separate identical laboratory sessions under 3 drug conditions: saline placebo, intravenous (i.v.) naloxone (opioid antagonist; 12-mg total), and i.v. morphine (0.09-mg/kg total). During each session, participants rated low-back pain intensity, evoked heat pain intensity, and nonpain subjective effects 4 times in sequence after incremental drug dosing. Mean morphine effects (morphine-placebo difference) and opioid blockade effects (naloxone-placebo difference; to index EO function) for each primary outcome (low-back pain intensity, evoked heat pain intensity, and nonpain subjective effects) were derived by averaging across the 4 incremental doses. The association between EO function and morphine-induced back pain relief was significantly moderated by endocannabinoids [2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA)]. Lower EO function predicted greater morphine analgesia only for those with relatively lower endocannabinoids. Endocannabinoids also significantly moderated EO effects on morphine-related changes in visual analog scale-evoked pain intensity (2-AG), drug liking (AEA and 2-AG), and desire to take again (AEA and 2-AG). In the absence of significant interactions, lower EO function predicted significantly greater morphine analgesia (as in past work) and euphoria. Results indicate that EO effects on analgesic and subjective responses to opioid medications are greatest when endocannabinoid levels are low. These findings may help guide development of mechanism-based predictors for personalized pain medicine algorithms.

Social learning pathways in the relation between parental chronic pain and daily pain severity and functional impairment in adolescents with functional abdominal pain

Having a parent with chronic pain (CP) may confer greater risk of persistence of CP from childhood into young adulthood. Social learning, such as parental modeling and reinforcement, represents one plausible mechanism for the transmission of risk of CP from parents to offspring. Based on a 7-day pain diary in 154 pediatric patients with functional abdominal CP, we tested a model in which parental CP predicted adolescents' daily average CP severity and functional impairment (distal outcomes) via parental modeling of pain behaviors and parental reinforcement of adolescent's pain behaviors (mediators) and adolescents' cognitive appraisals of pain threat (proximal outcome representing adolescents' encoding of parents' behaviors). Results indicated significant indirect pathways from parental CP status to adolescent average daily pain severity (b = 0.18, SE = 0.08, 95% confidence interval: 0.04-0.31, P = 0.03) and functional impairment (b = 0.08, SE = 0.04, 95% confidence interval: 0.02-0.15, P = 0.03) over the 7-day diary period via adolescents' observations of parent pain behaviors and adolescent pain threat appraisal. The indirect pathway through parental reinforcing responses to adolescents' pain did not reach significance for either adolescent pain severity or functional impairment. Identifying mechanisms of increased risk of pain and functional impairment in children of parents with CP ultimately could lead to targeted interventions aimed at improving functioning and quality of life in families with CP. Parental modeling of pain behaviors represents a potentially promising target for family-based interventions to ameliorate pediatric CP.

Adolescents' Observations of Parent Pain Behaviors: Preliminary Measure Validation and Test of Social Learning Theory in Pediatric Chronic Pain

Objective

Evaluate psychometric properties of a measure of adolescents’ observations of parental pain behaviors and use this measure to test hypotheses regarding pain-specific social learning.

Methods

We created a proxy-report of the Patient Reported Outcomes Measurement Information System (PROMIS) Pain Behavior–Short Form (PPB) for adolescents to report on parental pain behaviors, which we labeled the PPB-Proxy. Adolescents (n = 138, mean age = 14.20) with functional abdominal pain completed the PPB-Proxy and a parent completed the PPB. Adolescents and their parents completed measures of pain and disability during the adolescent’s clinic visit for abdominal pain. Adolescents subsequently completed a 7-day pain diary period.

Results

The PPB-Proxy moderately correlated with the PPB, evidencing that adolescents observe and can report on parental pain behaviors. Both the PPB-Proxy and PPB significantly correlated with adolescents’ pain-related disability.

Conclusions

Parental modeling of pain behaviors could represent an important target for assessment and treatment in pediatric chronic pain patients.

Expectancy Effects on Conditioned Pain Modulation Are Not Influenced by Naloxone or Morphine

BACKGROUND

Recent studies suggest that participant expectations influence pain ratings during conditioned pain modulation testing. The present study extends this work by examining expectancy effects among individuals with and without chronic back pain after administration of placebo, naloxone, or morphine.

PURPOSE

This study aims to identify the influence of individual differences in expectancy on changes in heat pain ratings obtained before, during, and after a forearm ischemic pain stimulus.

METHODS

Participants with chronic low back pain (n = 88) and healthy controls (n = 100) rated heat pain experience (i.e., "test stimulus") before, during, and after exposure to ischemic pain (i.e., "conditioning stimulus"). Prior to testing, participants indicated whether they anticipated that their heat pain would increase, decrease, or remain unchanged during ischemic pain.

RESULTS

Analysis of the effects of expectancy (pain increase, decrease, or no change), drug (placebo, naloxone, or morphine), and group (back pain, healthy) on changes in heat pain revealed a significant main effect of expectancy (p = 0.001), but no other significant main effects or interactions. Follow-up analyses revealed that individuals who expected lower pain during ischemia reported significantly larger decreases in heat pain as compared with those who expected either no change (p = 0.004) or increased pain (p = 0.001).

CONCLUSIONS

The present findings confirm that expectancy is an important contributor to conditioned pain modulation effects, and therefore significant caution is needed when interpreting findings that do not account for this individual difference. Opioid mechanisms do not appear to be involved in these expectancy effects.

Do Resting Plasma β-Endorphin Levels Predict Responses to Opioid Analgesics?

OBJECTIVES

Clinically feasible predictors of opioid analgesic responses for use in precision pain medicine protocols are needed. This study evaluated whether resting plasma β-endorphin (BE) levels predicted responses to an opioid analgesic, and whether chronic pain status or sex moderated these effects.

METHODS

Participants included 73 individuals with chronic low back pain (CLBP) and 88 pain-free controls, all using no daily opioid analgesics. Participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo, with blood samples obtained before drug administration to assay resting plasma BE levels. Once peak drug activity was achieved in each session, participants engaged in an ischemic forearm pain task (ISC) and a heat pain task. Morphine analgesic effects were derived reflecting the difference in pain outcomes between placebo and morphine conditions.

RESULTS

In hierarchical regressions, significant Type (CLBP vs. control)×BE interactions (Ps<0.05) were noted for morphine effects on ISC tolerance, ISC intratask pain ratings, and thermal VAS unpleasantness ratings. These interactions derived primarily from associations between higher BE levels and smaller morphine effects restricted to the CLBP subgroup. All other BE-related effects, including sex interactions, for predicting morphine analgesia failed to reach statistical significance.

DISCUSSION

BE was a predictor of morphine analgesia for only 3 out of 9 outcomes examined, with these effects moderated by chronic pain status but not sex. On the whole, results do not suggest that resting plasma BE levels are likely to be a clinically useful predictor of opioid analgesic responses.

Ethnic Differences in the Effects of Naloxone on Sustained Evoked Pain: A Preliminary Study

Ethnic differences in pain response have been well documented, with non-Hispanic Black (NHB) participants reporting enhanced clinical pain and greater laboratory-evoked pain sensitivity to a variety of quantitative sensory testing (QST) methods compared to non-Hispanic Whites (NHW). One potential mechanism that may contribute to these disparities is differential functioning of endogenous pain-regulatory systems. To evaluate endogenous opioid (EO) mechanisms in pain responses, we examined group differences in response to tonic capsaicin pain following double-blinded crossover administration of saline and the opioid antagonist, naloxone. Ten percent topical capsaicin cream and a thermode were applied to the dorsum of the non-dominant hand, maintaining a constant temperature of 40°C for 90 min. Naloxone (0.1 mg/kg) or saline placebo was administered at the 25 min mark and post-drug pain intensity ratings were obtained every 5 min thereafter. As an index of EO function, blockade effects were derived for each participant, reflecting the difference between mean post-drug pain intensity ratings under the saline versus naloxone conditions, with higher positive scores reflecting greater EO inhibition of pain. Thirty-nine healthy, young individuals (19 non-Hispanic Black [NHB], 20 non-Hispanic White [NHW]) participated. Group difference in EO function were identified, with NHB participants displaying lower EO function scores (mean=-10.8, SD=10.1) as compared to NHW participants (mean=-0.89, SD=11.5; p=0.038). NHB participants experienced significant paradoxical analgesia with naloxone. Thirty five percent of the NHW participants showed a positive blockade effect indicating EO analgesia (i.e., an increase in pain with naloxone), while only 10% of the NHB participants exhibited evidence of EO analgesia. These findings suggest differential functioning of the endogenous opioid pain regulatory system between NHB and NHW participants. Future research is warranted to examine whether these differences contribute to the disparities observed in clinical pain between groups.

The Contribution of Differential Opioid Responsiveness to Identification of Opioid Risk in Chronic Pain Patients

The Screener and Opioid Assessment for Patients with Pain-Revised (SOAPP-R) predicts increased risk of opioid misuse in chronic pain patients. We evaluated whether higher SOAPP-R scores are associated with greater opioid reinforcing properties, potentially contributing to their predictive utility. Across 2 counterbalanced laboratory sessions, 55 chronic low back pain sufferers completed the SOAPP-R at baseline and measures of back pain intensity, evoked pain responsiveness (thermal, ischemic), and subjective opioid effects after receiving intravenous morphine (.08 mg/kg) or saline placebo. Morphine effect measures were derived for all outcomes, reflecting the difference between morphine and placebo condition values. Higher SOAPP-R scores were significantly associated with greater desire to take morphine again, less feeling down and feeling bad, and greater reductions in sensory low back pain intensity following morphine administration. This latter effect was due primarily to SOAPP-R content assessing medication-specific attitudes and behavior. Individuals exceeding the clinical cutoff (18 or higher) on the SOAPP-R exhibited significantly greater morphine liking, desire to take morphine again, and feeling sedated; less feeling bad; and greater reductions in sensory low back pain following morphine. The SOAPP-R may predict elevated opioid risk in part by tapping into individual differences in opioid reinforcing effects.

PERSPECTIVE

Based on placebo-controlled morphine responses, associations were observed between higher scores on a common opioid risk screener (SOAPP-R) and greater desire to take morphine again, fewer negative subjective morphine effects, and greater analgesia. Opioids may provide the best analgesia in those patients at greatest risk of opioid misuse.

Relationship between endogenous opioid function and opioid analgesic adverse effects

BACKGROUND AND OBJECTIVES

Our recent work indicates that endogenous opioid activity influences analgesic responses to opioid medications. This secondary analysis evaluated whether endogenous opioid activity is associated with degree of opioid analgesic adverse effects, and whether chronic pain status and sex affect these adverse effects.

METHODS

Using a double-blind, randomized, placebo-controlled, crossover design, 51 subjects with chronic low back pain and 38 healthy controls participated in 3 separate sessions, undergoing 2 laboratory-evoked pain tasks (ischemic and thermal) after receiving placebo, naloxone, or morphine. Endogenous opioid system function was indexed by the difference in pain responses between the placebo and naloxone conditions. These measures were examined for associations with morphine-related adverse effects.

RESULTS

Chronic pain subjects reported significantly greater itching and unpleasant bodily sensations with morphine than controls (P < 0.05). Across groups, only 6 of 112 possible associations between adverse effects and blockade effects were significant. For the ischemic task, higher endogenous opioid function was associated with greater itching (visual analog scale [VAS]; P < 0.05), numbness (tolerance; P < 0.001), dry mouth (tolerance; P < 0.05), and unpleasant bodily sensations (VAS; P < 0.05). For the thermal task, higher endogenous opioid function was associated with greater numbness (VAS; P < 0.05) and feeling carefree (VAS; P < 0.05). There were no significant main or interaction effects of chronic pain status or sex on these findings.

CONCLUSIONS

No consistent relationships were observed between endogenous opioid function and morphine-related adverse effects. This is in stark contrast to our previous observation of strong relationships between elevated endogenous opioid function and smaller morphine analgesic effects.

Alterations in endogenous opioid functional measures in chronic back pain

The absence of consistent end organ abnormalities in many chronic pain syndromes has led to a search for maladaptive CNS mechanisms that may explain their clinical presentations and course. Here, we addressed the role of brain regional μ-opioid receptor-mediated neurotransmission, one of the best recognized mechanisms of pain regulation, in chronic back pain in human subjects. We compared μ-opioid receptor availability in vivo at baseline, during pain expectation, and with moderate levels of sustained pain in 16 patients with chronic nonspecific back pain (CNBP) and in 16 age- and gender-matched healthy control subjects, using the μ-opioid receptor-selective radioligand [(11)C]carfentanil and positron emission tomography. We found that CNBP patients showed baseline increases in thalamic μ-opioid receptor availability, contrary to a previously studied sample of patients diagnosed with fibromyalgia. During both pain expectation and sustained pain challenges, CNBP patients showed regional reductions in the capacity to activate this neurotransmitter system compared with their control sample, further associated with clinical pain and affective state ratings. Our results demonstrate heterogeneity in endogenous opioid system functional measures across pain conditions, and alterations in both receptor availability and endogenous opioid function in CNBP that are relevant to the clinical presentation of these patients and the effects of opioid analgesics on μ-opioid receptors.

Endogenous opioid function mediates the association between laboratory-evoked pain sensitivity and morphine analgesic responses

Predictors of responsiveness to opioid analgesic medications are not well understood. This study tested whether individual differences in endogenous opioid (EO) function are associated with analgesic responsiveness to morphine. In randomized, counterbalanced order over 3 sessions, 45 chronic low back pain participants and 31 healthy controls received an opioid antagonist (8 mg naloxone), morphine (0.08 mg/kg), or placebo. Participants then engaged in 2 laboratory-evoked pain tasks (ischemic and thermal). Outcomes included pain threshold, pain tolerance, and pain ratings. Indexes of EO function and morphine analgesic responsiveness were derived for each measure as the difference in pain responses between the placebo condition and naloxone or morphine condition, respectively. For all 7 pain measures across the 2 laboratory pain tasks, greater EO function was associated with significantly lower morphine analgesic responsiveness (P<0.001-P=0.02). Morphine reduced pain responses of low EO individuals to levels similar to those of high EO individuals receiving placebo. Higher placebo condition-evoked pain sensitivity was associated with significantly greater morphine analgesic responsiveness for 5 of 7 pain measures (P<0.001-P=0.02). These latter associations were significantly mediated by EO function for 4 of these 5 pain outcomes (all P values<0.05). In the laboratory-evoked pain context, opioid analgesic medications may supplement inadequate EO analgesia, with little incremental benefit in those with preexisting high EO function. Implications for personalized medicine are discussed.

Individual and additive effects of mothers' and fathers' chronic pain on health outcomes in young adults with a childhood history of functional abdominal pain

OBJECTIVE

To evaluate effects of mothers' and fathers' chronic pain on health outcomes in adult sons and daughters with a childhood history of functional abdominal pain (FAP).

METHOD

Adults (n = 319; Mean age = 22.09 years) with a childhood history of FAP reported parental history of chronic pain and their own current health (chronic pain, somatic symptoms, disability, use of medication and health care, illness-related job loss).

RESULTS

Positive histories of maternal and paternal chronic pain were each associated with poorer health in sons and daughters, regardless of child or parent gender. Having 2 parents with chronic pain was associated with significantly poorer health than having 1 or neither parent with chronic pain.

CONCLUSIONS

Chronic pain in both mothers and fathers is associated with poor health and elevated health service use in young adults with a childhood history of FAP. Having both parents with chronic pain increases risk for adverse outcomes.

Hypertension prevalence and diminished blood pressure-related hypoalgesia in individuals reporting chronic pain in a general population: the Tromsø study

Resting blood pressure (BP) is inversely related to pain sensitivity in individuals free of chronic pain, reflecting homeostatic interactions between cardiovascular and pain modulatory systems. Several laboratory studies indicate that BP-related hypoalgesia is diminished in chronic pain patients, suggesting dysfunction in these interacting systems. Separate epidemiological findings reveal elevated hypertension prevalence in the chronic pain population. This study for the first time simultaneously evaluated both hypertension prevalence and BP-related hypoalgesia as they relate to chronic pain in the same sample. Resting BP and pain sensitivity were evaluated in a large general population sample (n=10,135, aged 30-87years). Subjects participated in a standardized 106s cold pressor test, providing pain ratings at 9s intervals. Self-reported presence of chronic pain and history of hypertension and use of antihypertensive medication were assessed. Significant interactions between chronic pain status and resting systolic (P<.001) and diastolic BP (P<.001) on mean pain ratings were observed. These interactions were due to significant (P<.001) BP-related hypoalgesia in individuals free of chronic pain that was twice the magnitude of the hypoalgesia observed in the group reporting chronic pain. Presence of chronic pain was associated with significantly increased odds of comorbid hypertension (P<.001). Within the chronic pain group, higher chronic pain intensity was a significant predictor of positive hypertension status beyond the effects of traditional demographic risk factors (P<.05). Results are consistent with the hypothesis that increased hypertension risk in the chronic pain population might be linked in part to chronic pain-related dysfunction in interacting cardiovascular-pain modulatory systems.

Associations between daily chronic pain intensity, daily anger expression, and trait anger expressiveness: an ecological momentary assessment study

Links between elevated trait anger expressiveness (anger-out) and greater chronic pain intensity are well documented, but pain-related effects of expressive behaviors actually used to regulate anger when it is experienced have been little explored. This study used ecological momentary assessment methods to explore prospective associations between daily behavioral anger expression and daily chronic pain intensity. Forty-eight chronic low back pain (LBP) patients and 36 healthy controls completed electronic diary ratings of momentary pain and behavioral anger expression in response to random prompts 4 times daily for 7 days. Across groups, greater trait anger-out was associated with greater daily behavioral anger expression (P<0.001). LBP participants showed higher levels of daily anger expression than controls (P<0.001). Generalized estimating equation analyses in the LBP group revealed a lagged main effect of greater behavioral anger expression on increased chronic pain intensity in the subsequent assessment period (P<0.05). Examination of a trait×situation model for anger-out revealed prospective associations between elevated chronic pain intensity and later increases in behavioral anger expression that were restricted largely to individuals low in trait anger-out (P<0.001). Trait×situation interactions for trait anger suppression (anger-in) indicated similar influences of pain intensity on subsequent behavioral anger expression occurring among low anger-in persons (P<0.001). Overlap with trait and state negative affect did not account for study findings. This study for the first time documents lagged within-day influences of behavioral anger expression on subsequent chronic pain intensity. Trait anger regulation style may moderate associations between behavioral anger expression and chronic pain intensity.

What do plasma beta-endorphin levels reveal about endogenous opioid analgesic function?

Plasma levels of beta-endorphin (BE), an endogenous opioid analgesic, are often reported as they relate to acute and chronic pain outcomes. However, little is known about what resting plasma BE levels might reveal about functioning of the endogenous opioid antinociceptive system. This study directly examined associations between resting plasma BE and subsequent endogenous opioid analgesic responses to acute pain in 39 healthy controls and 37 individuals with chronic low back pain (LBP). Resting baseline levels of plasma BE were assessed. Next, participants received opioid blockade (8 mg naloxone i.v.) or placebo in a double-blind, randomized, crossover design. Participants then underwent two acute pain stimuli: finger pressure (FP) pain and ischaemic (ISC) forearm pain. Blockade effects (naloxone minus placebo pain ratings) were derived to index endogenous opioid analgesic function. In placebo condition analyses for both pain stimuli, higher resting BE levels were associated with subsequently greater reported pain intensity (p's < 0.05), with this effect occurring primarily in healthy controls (BE × Participant Type interactions, p's < 0.05). In blockade effect analyses across both pain tasks, higher resting plasma BE predicted less subsequent endogenous opioid analgesia (smaller blockade effects; p's < 0.05). For the ISC task, these links were significantly more prominent in LBP participants (BE × Participant Type Interactions, p's < 0.05). Results suggest that elevated resting plasma BE may be a potential biomarker for reduced endogenous opioid analgesic capacity, particularly among individuals with chronic pain. Potential clinical implications are discussed.

Thermal sensitivity and cardiovascular reactivity to stress in healthy males

This paper examines the association of cardiovascular reactivity with thermal thresholds (detection and unpleasantness). Heart period (HP), systolic (SBP) and diastolic (DBP) blood pressure of 42 health young males were recorded during a cardiovascular reactivity task (a videogame based upon Sidman's avoidance paradigm). Thermal sensitivity, assessing detection and unpleasantness thresholds with radiant heat in the forearm was also estimated for participants. Participants with differential scores in the cardiovascular variables from base line to task > or = P65 were considered as reactors and those how have differential scores < or = P35 were considered as non-reactors. Significant differences were observed between groups in the unpleasantness thresholds in blood pressure (BP) but not in HP. Reactors exhibited significant higher unpleasantness thresholds than non-reactors. No significant differences were obtained in detection thresholds between groups.

Interacting effects of trait anger and acute anger arousal on pain: the role of endogenous opioids

OBJECTIVE

Elevated trait anger (TRANG; heightened propensity to experience anger) is associated with greater pain responsiveness, possibly via associations with deficient endogenous opioid analgesia. This study tested whether acute anger arousal moderates the impact of TRANG on endogenous opioid analgesia.

METHODS

Ninety-four chronic low back pain (LBP) participants and 85 healthy controls received opioid blockade (8 mg of naloxone) or placebo in a randomized, counterbalanced order in separate sessions. Participants were randomly assigned to undergo either a 5-minute anger recall interview (ARI) or a neutral control interview across both drug conditions. Immediately after the assigned interview, participants engaged sequentially in finger pressure and ischemic forearm pain tasks. Opioid blockade effects were derived (blockade minus placebo condition pain ratings) to index opioid antinociceptive function.

RESULTS

Placebo condition TRANG by interview interactions (p values < .05) indicated that TRANG was hyperalgesic only in the context of acute anger arousal (ARI condition; p values < .05). Blockade effect analyses suggested that these hyperalgesic effects were related to deficient opioid analgesia. Significant TRANG by interview interactions (p values < .05) for both pain tasks indicated that elevated TRANG was associated with smaller blockade effects (less endogenous opioid analgesia) only in the ARI condition (p values < .05). Results for ischemic task visual analog scale intensity blockade effects suggested that associations between TRANG and impaired opioid function were most evident in LBP participants when experiencing anger (type by interview by TRANG interaction; p < .05).

CONCLUSIONS

Results indicate that hyperalgesic effects of TRANG are most prominent when acute anger is aroused and suggest that endogenous opioid mechanisms contribute.

Chronic pain-related changes in endogenous opioid analgesia: a case report

This case report presents data regarding endogenous opioid analgesia in a healthy female subject prior to developing chronic pain, and again 4 and 13 months following onset of chronic daily back pain. At each assessment period, the subject underwent identical protocols involving two sessions one week apart with randomized double-blind crossover administration of saline placebo and naloxone, an opioid antagonist. Each session included a 5-min anger recall interview, followed by finger pressure and ischemic acute pain tasks. Increases in acute pain ratings induced by opioid blockade were interpreted as reflecting endogenous opioid analgesia. When the subject was healthy and pain-free, naloxone produced a mean overall 16% decrease in pain ratings relative to placebo. However, 4 months after onset of chronic pain, a mean naloxone-induced increase of 22% in pain ratings over placebo was observed, consistent with presence of endogenous opioid analgesia. The mean magnitude of this opioid blockade effect for the finger pressure task exceeded the 99% confidence interval for the healthy control population based on a previous study using a similar opioid blockade protocol [4]. At 13-month follow-up, naloxone produced a mean 45% decrease in acute pain ratings compared to placebo, arguing against presence of endogenous opioid analgesia. Although results must be interpreted cautiously, findings are consistent with the hypothesis that chronic pain may initially be associated with upregulation of endogenous opioid analgesic systems which then may become dysfunctional over time.

Neuroimaging the genomics of pain processing--a perspective

The significant inter-individual variability in pain behavior and its contributing factors remains a pervasive clinical challenge and has generated intense scientific investigations in this field. Recent studies indicate that our genes considerably influence nociceptive information processes, how our nociceptive system copes with peripheral injury, and the individual response to analgesic treatments. Neuroimaging studies of pain are beginning to link such genetic influences with physiological processes in the human brain. This review presents the pioneering endeavors of the hybrid approach of neuroimaging pain genes in humans and identifies potential future directions.

Progress in genetic studies of pain and analgesia

Interindividual variability in pain sensitivity and the response to analgesic manipulations remains a considerable clinical challenge as well as an area of intense scientific investigation. Techniques in this field have matured rapidly so that much relevant data have emerged only in the past few years. Our increasing understanding of the genetic mediation of these biological phenomena have nonetheless revealed their surprising complexity. This review provides a comprehensive picture and critical analysis of the field and its prospects.

Postoperative pain patterns in chronic pain patients: a pilot study

OBJECTIVE

This exploratory investigation compared patterns of postoperative pain over 6 days in normal patients recovering from surgery with those of patients using opioid medications for chronic pain. It tested the following hypotheses: 1) Chronic pain patients have a different pattern of postoperative pain than normals; 2) Women have a different pattern of postoperative pain resolution than men.

PATIENTS

Normal (N = 96) and chronic pain (N = 42) patients undergoing surgery served as subjects.

DESIGN

The study employed a linear mixed effects model to compare repeated measures of pain in the two patient groups.

OUTCOME MEASURES

Patients rated pain daily following surgery over 6 days. Each patient's pain pattern is a linear trend having an intercept (initial pain level) and a slope (rate of pain change over days).

RESULTS

The chronic pain patients initially reported a higher mean pain level, and they differed from normal patients in their average postoperative pain patterns (P < 0.001), as did men and women (P = 0.039). Whereas normals decreased in pain report over the 6 days of recovery at an average rate of -0.35 units per day, chronic pain patients changed at an average rate of only -0.06 units per day (P < 0.001). Women began at day 0 with greater average pain than men (6.15 vs 5.16, P = 0.029) but resolved their pain more rapidly (-0.291 points per day vs -0.118 points per day, P = 0.017).

CONCLUSIONS

Surgical patients who have chronic pain and use opioid medications for that pain have more postoperative pain than normals and resolve that pain more slowly.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Heritability of responses to painful stimuli in women: a classical twin study

There is as yet no conclusive evidence for the heritability of pain sensitivity in humans. We performed a classical twin study to evaluate the relative contributions of genetic and environmental factors on responses to painful stimuli in women. Ninety-eight pairs of twins, 51 monozygotic (MZ) and 47 dizygotic (DZ), were recruited from the TwinsUK adult registry held at St Thomas' Hospital, London. The correlation of quantitative sensory testing scores for the different responses to painful stimuli were compared between the MZ and DZ twin pairs and structural equation modelling was used to provide an estimate of the heritability. Statistically significant genetic components (varying between 22 and 55%) were seen for the responses to the majority of painful stimuli including: heat pain threshold (HPT), the pain rating during induction of a thermal burn, the secondary areas of punctate hyperalgesia and brush evoked allodynia following the induction of a 45 degrees C thermal burn, and the pain ratings during the iontophoresis of adenosine triphosphate (ATP) and acid. The area of skin flare following thermal burn induction did not have a significant genetic component; rather common environmental factors provided the greatest contribution (65%). In our experiment neither shared genetic nor environmental features were significant in determining the extent of thermal sensitisation. In summary we show that sensitivity to a variety of experimental thermal, mechanical and chemical pain-producing stimuli has a genetic contribution. Our study demonstrates the importance of genetic factors in determining human experimental pain sensitivity, and opens the way for its use as a phenotype in gene discovery. Since experimental pain sensitivity is known to be a predictor for pathological pain, our data imply that genetic factors have an important aetiological contribution towards clinical pain states.

Nociceptive flexion reflex and pain rating responses during endogenous opiate blockade with naltrexone in healthy young adults

The effect of opioid blockade on nociceptive flexion reflex (NFR) activity and subjective pain ratings was examined in 151 healthy young men and women. Using a within-subjects design, NFR threshold was assessed on 2 days after administration of either placebo or a 50mg dose of naltrexone. Electrocutaneous pain threshold and tolerance levels were measured after NFR threshold assessment on each day. Results indicated that administration of naltrexone was consistently associated with hypoalgesic responding. Specifically, participants exhibited lower levels of NFR activity and reported lower pain ratings for electrocutaneous stimulation delivered at pain threshold and tolerance levels following administration of naltrexone as compared to placebo. These findings indicate that opiate blockade using the current standard dose may elicit hypoalgesia. A potential moderating effect of dose of opiate-blockade medication and level of endogenous opioid activation should be carefully examined in future research.