Acute alcohol effects on conditioned pain modulation, but not temporal summation of pain

Exploring the Spectrum of Temporal Summation and Conditioned Pain Modulation Responses in Pain-Free Individuals Using a Tonic Heat Pain and Cold Pressor Test Paradigms

BACKGROUND

Temporal summation (TS) and conditioned pain modulation (CPM) are impaired in many chronic pain individuals, although typical TS and CPM responses remain unclear. Providing a quantile distribution of TS and CPM values could help determine whether TS and CPM responses fall outside the usual ranges, thereby informing pain management strategies. The objective of this study was to provide a response distribution for these mechanisms in a large, pain-free cohort.

METHODS

Pain-free participants (n = 347) were evaluated. TS was interpreted as the change in pain perception scores during a constant heat pain stimulus. CPM was assessed by the difference in pain perception scores induced by a tonic heat pain stimulus and a mechanical pain threshold, before and after a cold pressor test (CPT). Quantile regression was performed to identify the 5th to 95th percentiles, with a specific focus on the 75th, 90th and 95th percentiles and their confidence intervals, while considering age and sex.

RESULTS

Analyses revealed a particularly large range of TS and CPM responses, spanning from strong inhibition in CPM and strong summation in TS to moderate or even null effects. Notably, some responses deviated from the expected patterns, with certain individuals exhibiting hyperalgesic CPM effects and others displaying hypoalgesic TS responses. The highest percentiles of the TS distribution were influenced by age and gender, while CPM scores remained unchanged.

CONCLUSION

The results of this study provide an overview of the possible spectra of responses for TS and CPM, potentially paving the way for their incorporation into pain management strategies.

SIGNIFICANCE STATEMENT

This study examines the spectrum and provides a distribution for TS and CPM values to better identify what may constitute a deficit in these mechanisms and enhance their clinical interpretation.

TRIAL REGISTRATION

clinicaltrial.gov identifier: NCT03376867.

Associations between mental health and cervical, thoracic, and lumbar back pain in adolescents: A cross-sectional study

BACKGROUND

Low back pain is a significant emergent health disorder in adolescence. It is predicted that around 843 million subjects worldwide will present this condition in 2050. We investigated whether symptoms of anxiety, depression, and suicidal behavior are associated with back pain in adolescents.

METHODS

This is a cross-sectional school-based study including 4514 student participants aged 14-19 years. Data were collected using the WHO's "Global School-Based Student Health Survey". Anxiety symptoms were assessed with the Social Anxiety Scale for Adolescents. The Depression Scale of the Center for Epidemiologic Studies was used to estimate depressive symptomatology. Suicidal behaviors were assessed with two questions about thoughts and plans for suicide. The presence (yes, no) of each of cervical, thoracic, and lumbar back pain were assessed with the use of a drawing of the human body with spine areas delimited. Multivariable logistic regression analyses were used to study the presence of three outcomes of back pain (cervical, thoracic, and lumbar) and associated factors.

RESULTS

Adolescents with cervical pain were more likely to report social anxiety (OR = 1.0, CI: 1.00-1.02). Depression symptomatology was associated with pain in the tree segments of the spine: cervical (OR = 1.01, CI: 1.00-1.02), thoracic (OR = 1.02, CI: 1.01-1.02), and lumbar (OR = 1.02, CI: 1.01-1.02). No association was observed between suicidal behavior and cervical (OR = 0.86 CI: 0.743-1.017), thoracic (OR = 0.92, CI: 0.79-1.08), and lumbar back pain (OR = 0.86, CI: 0.73-1.01).

LIMITATIONS

It is not possible to affirm causality in the interpretation of findings.

CONCLUSIONS

Social anxiety and depression symptomatology were associated with back pain in adolescents.

Conditioned pain modulation elicited through manual pressure techniques on the cervical spine: a crossover study

Introduction

Manual pressure techniques are commonly employed as a therapeutic approach for individuals experiencing musculoskeletal pain. The painful nature of these techniques suggests that a central mechanism known as conditioned pain modulation (CPM) might play a role.

Objectives

This study tested whether a painful manual pressure technique (MPT) reduces pain sensitivity partly by eliciting a CPM effect.

Methods

This crossover study examined 3 different conditioning stimuli: (1) a cold pressor test (CPT) with the contralateral hand submerged in a cold water bath, (2) painful MPT, and (3) sham-MPT on suboccipital muscles. We measured their effect on pain sensitivity using pressure pain thresholds at 3 locations: locally (suboccipital muscles), regionally (trapezius muscle), and remotely (tibialis anterior muscle).

Results

In 63 healthy participants, no significant differences were found between the painful MPT and CPT on the pressure pain thresholds at all test locations: locally, -11 kPa (95% CI: 3 to -25); regionally, -15 kPa (95% CI: 10 to -39); and remotely, -24 kPa (95% CI: 55 to -7). Manual pressure technique compared to sham-MPT showed significant differences in the suboccipital muscles, -20.04 kPa (95% CI: -6.45 to -34.63) and the trapezius muscle, -38.24 (95% CI: -13.97 to -62.5) but no significant difference at the tibialis anterior muscle, -17.5 kPa (95% CI: 13.9 to -48.91).

Conclusion

Painful MPTs applied at the suboccipital muscles reduce pain sensitivity at all sites, similar to the CPT, indicating CPM activation. Central pain inhibition might contribute to the effect of painful MPT in healthy people.

Dose-dependent effects of alcohol consumption on pressure pain threshold

INTRODUCTION

Prior laboratory-based studies have identified significant analgesic effects of acute alcohol. Despite providing excellent experimental control, these studies are limited regarding the range of alcohol exposure that can be practically and ethically achieved. This study capitalized on the heterogeneity in breath alcohol concentration (BrAC) resulting from naturalistic alcohol use at a public event to improve understanding of alcohol analgesia. We hypothesized that BrAC would be significantly and positively associated with pain threshold.

METHODS

Participants were attendees of the 2024 Minnesota State Fair reporting alcohol use within the last month (N = 149, 55 % women). Each completed a brief assessment of pressure pain threshold at the first dorsal interosseus muscle. BrAC was measured using a standard breathalyzer device. Hierarchical multiple regression analysis characterized BrAC as a predictor of pain threshold, controlling for covariates including clinical pain, age, sex, typical drinking, participant/experimenter gender matching, and expectancies of alcohol analgesia.

RESULTS

30.9 % of participants had non-zero BrACs, with an average of 0.038 g/dL. Average pain threshold was 3.58 kgf/cm2. Higher BrAC predicted greater pain threshold in both the whole sample (b = 0.145, p = 0.001, η2p = 0.07) and those participants with non-zero BrACs (b = 0.184, p = 0.009, η2p = 0.18). Men had significant greater pain thresholds than women (p = 0.007, η2p = 0.052), but no other covariates reached significance. Addition of quadratic and cubic BrAC terms did not improve model fit.

DISCUSSION

Results suggest a significant, dose-dependent association of alcohol use with increased pain threshold, independent of age, sex, number of reported pain conditions, participant/experimenter gender matching, or beliefs regarding alcohol analgesia. The acute analgesic effects of alcohol may scale linearly with amount consumed, at least within the BrAC range observed in the study.

Effects of Apnea-Induced Hypoxia on Hypoalgesia in Healthy Subjects

INTRODUCTION

Exercise-induced hypoalgesia is a phenomenon in which exercise bouts induce a reduction in pain sensitivity. Apnea training involves similar characteristics that could potentially induce hypoalgesia.

OBJECTIVES

The objectives of this study are to explore the effect of apnea training on hypoalgesia; assess the correlation between conditioned pain modulation (CPM) response and apnea-induced hypoalgesia; and examine the association between hypoalgesia with hypoxemia, and heart rate (HR) during apnea.

METHODS

A randomized controlled trial was conducted comparing a walking protocol employing intermittent apnea compared with normal breathing in healthy volunteers. Hypoalgesia was tested with pressure pain thresholds (PPTs) and CPM. Oxygen saturation (SpO2) and HR were also tested.

RESULTS

Relevant but not significant changes were detected in the thumb (MD = 0.678 kg/cm2), and tibialis (MD = 0.718 kg/cm2) in favor of the apnea group. No significant differences were detected in CPM. The apnea group presented lower SpO2, but HR values similar to those of the control group during the intervention. Basal CPM and intrasession hypoxemia significantly correlated with the PPT response. However, HR did not correlate with the PPT response.

CONCLUSIONS

The current results suggest a trend, though not statistically significant, toward an improvement in the PPT in favor of apnea training compared to normal breathing. Nevertheless, subjects who presented greater basal CPM and lower oxygen saturation during the session presented a greater PPT response, suggesting the possibility of mediators of response. Future investigations should clarify this phenomenon.

Change in Endogenous Pain Modulation Depending on Emotional States in Healthy Subjects: A Randomized Controlled Trial

INTRODUCTION

Chronic pain is a public health issue, leading to substantial healthcare costs and diminished quality of life for sufferers. While the role of anxiety in pain modulation has been extensively studied, the effects of other emotional states on the body's pain control mechanisms remain less understood. This study sought to explore how different emotions (happiness, anger, sadness, and interest) affect conditioned pain modulation (CPM) and the wind-up phenomenon in healthy adults.

METHODS

This randomized controlled, cross-over trial involved 28 healthy participants aged 18-60. Participants watched video clips designed to induce specific emotions: happiness, anger, sadness, and interest. Emotional states were assessed using a 7-point Likert scale. Pain modulation was measured using CPM and the wind-up phenomenon. CPM was assessed with a hot water bath as the conditioning stimulus and pressure pain tolerance as the test stimulus. Wind-up was measured using pinprick needle stimulators and a visual analog scale. Data were analyzed using paired t tests to compare pre- and post-emotion induction values.

RESULTS

Significant changes in emotional self-assessment values were observed for all emotions. Happiness increased CPM (4.6 ± 11.4, p = 0.04277), while sadness - 9.9 ± 23.1, p = 0.03211) and anger - 9.1 ± 23.3, p = 0.04804) decreased it. Interest did not significantly alter CPM (- 5.1 ± 25.8, p = 0.31042). No significant effects were found for the wind-up phenomenon across any emotional states.

CONCLUSION

This study shows that emotional states significantly affect the body's ability to modulate pain. Positive emotions like happiness enhance pain inhibition, while negative emotions such as sadness and anger impair it. These findings suggest that emotional modulation techniques could be integrated into pain management strategies to improve patient outcomes. Further research should explore a broader range of emotions and include objective measures to validate these results.

Neural and Psychosocial Mechanisms Underlying Alcohol Use and Pain Interactions: Overview of Current Evidence and Future Directions

Purpose of Review

A growing body of research indicates bidirectional associations between alcohol use and pain. In this review, we highlight common neural and psychosocial mechanisms underlying pain and alcohol use and identify current gaps in the literature regarding alcohol/pain interactions. We also suggest future directions for the field moving forward, including more nuanced conceptualization of alcohol's negative reinforcing effects in the context of pain, broader use of clinically-relevant experimental pain induction modalities, and characterization of age, biological sex, gender, race, and ethnicity as moderators of pain/alcohol interactions.

Recent Findings

Acute alcohol intake has analgesic and negative-reinforcing effects in the context of pain, and chronic heavy alcohol use appears to increase risk for development of chronic pain. At the same time, pain, both acute and chronic, acts as a proximal antecedent for alcohol use and is associated with relapse risk for individuals in recovery from alcohol use disorder.

Summary

Although the links between alcohol use and pain are increasingly appreciated, significant gaps in understanding remain and systematic study of alcohol/pain interactions at all levels, including basic, preclinical, translational, and interventional, is needed.

Electroencephalography-Based Effects of Acute Alcohol Intake on the Pain Matrix

The effects of acute and chronic intakes of high doses of alcohol on pain perception are well known, ranging from short-term analgesic effects to long-term sensitization and polyneuropathies. The short-term analgesic effects of ethanol consumption on subjective pain perception have been well studied in the literature. Recent advances in neuroimaging allow for an insight into pain-related structures in the brain, fostering the mechanistic understanding of the processing of nociceptive input and pain. We aimed to utilize EEG, combined with standardized noxious mechanical/thermal stimulation and subjective pain testing, to research the effects of acute alcohol intake on nociceptive processing and pain perception. We recruited 12 healthy subjects in an unblinded cross-over study design and aimed at achieving a blood alcohol level of 0.1%. Our data revealed a significant reduction in subjective pain ratings to noxious thermal and mechanical stimuli after alcohol ingestion. Our EEG data revealed suppressing effects on the cortical structures responsible for processing pain, the "pain matrix". We conclude that in addition to its analgesic effects, as expressed by the reduction in subjective pain, alcohol has a further impact on the "pain matrix" and directly affects the salience to a nociceptive stimulus.

The Effect of Praying on Endogenous Pain Modulation and Pain Intensity in Healthy Religious Individuals in Lebanon: A Randomized Controlled Trial

Prayer is considered to be the most common therapy used in alternative medicine. This study aimed to explore the effect of prayers on endogenous pain modulation, pain intensity, and sensitivity in healthy religious participants. A total of 208 healthy religious participants were enrolled in this study and randomly distributed into two groups, a prayer group (n = 156) and a poem reading or control group (n = 52). Participants from the prayer group were then selectively allocated using the prayer function scale to either an active prayer group (n = 94) receiving an active type of praying or to a passive prayer group (n = 62) receiving a passive type of praying. Pain assessments were performed before and following the interventions and included pressure pain threshold assessment (PPT), conditioned pain modulation (CPM), and a numerical pain rating scale. A significant group-by-time interaction for PPT (p = 0.014) indicated post-intervention increases in PPT in the prayer group but not in the poem reading control group. Participants experienced a decrease in CPM efficacy (p = 0.030) and a reduction in their NPRS (p < 0.001) following the interventions, independent of their group allocation. The results showed that prayer, irrespective of the type, can positively affect pain sensitivity and intensity, but does not influence endogenous pain inhibition during hot water immersion. Future research should focus on understanding the mechanism behind "prayer-induced analgesia."

Analgesic effects of alcohol in adults with chronic jaw pain

BACKGROUND

Although recent literature provides promising support for the analgesic properties of alcohol, potential differences in alcohol analgesia as a function of chronic pain status are not well understood. Thus, this study examined chronic pain status as a potential moderator of alcohol analgesia and distinguished between multiple aspects of pain experience and sensitivity: pain threshold, pain intensity, pain unpleasantness, and perceived relief.

METHODS

Social drinkers with (N = 19) and without (N = 29) chronic jaw pain completed two testing sessions in a counterbalanced order: alcohol (target BrAC = 0.08 g/dl) and placebo. In each, pressure algometry was performed at the insertion of the masseter. Alcohol analgesia was assessed by examining the main and interactive effects of beverage condition, pressure level (4, 5, or 6 pound-feet [lbf]), and chronic jaw pain status (chronic pain vs. pain-free control) on quantitative sensory testing measures and pain relief ratings following noxious stimuli.

RESULTS

Analyses indicated significant increases in pain threshold and pain relief and reductions in pain unpleasantness and pain intensity, under the alcohol condition. Chronic pain participants demonstrated lower pain thresholds and greater pain intensity and pain unpleasantness ratings than controls. There were no interactive effects of alcohol and pain conditions on any pain measure.

CONCLUSIONS

Findings provide experimental evidence of alcohol's analgesic and pain-relieving effects and suggest that these effects do not significantly differ by chronic pain status. Individuals, who self-medicate pain via alcohol consumption, irrespective of pain status, may be at increased risk to engage in hazardous drinking patterns and thus experience adverse alcohol-related consequences.

Exposure to an Immersive Virtual Reality Environment can Modulate Perceptual Correlates of Endogenous Analgesia and Central Sensitization in Healthy Volunteers

Virtual reality (VR) has been shown to produce analgesic effects during different experimental and clinical pain states. Despite this, the top-down mechanisms are still poorly understood. In this study, we examined the influence of both a real and sham (ie, the same images in 2D) immersive arctic VR environment on conditioned pain modulation (CPM) and in a human surrogate model of central sensitization in 38 healthy volunteers. CPM and acute heat pain thresholds were assessed before and during VR/sham exposure in the absence of any sensitization. In a follow-on study, we used the cutaneous high frequency stimulation model of central sensitization and measured changes in mechanical pain sensitivity in an area of heterotopic sensitization before and during VR/sham exposure. There was an increase in CPM efficiency during the VR condition compared to baseline (P < .01). In the sham condition, there was a decrease in CPM efficiency compared to baseline (P < .01) and the real VR condition (P < .001). Neither real nor sham VR had any effect on pain ratings reported during the conditioning period or on heat pain threshold. There was also an attenuation of mechanical pain sensitivity during the VR condition indicating a lower sensitivity compared to sham (P < .05). We conclude that exposure to an immersive VR environment has no effect over acute pain thresholds but can modulate dynamic CPM responses and mechanical hypersensitivity in healthy volunteers. PERSPECTIVE: This study has demonstrated that exposure to an immersive virtual reality environment can modulate perceptual correlates of endogenous pain modulation and secondary hyperalgesia in a human surrogate pain model. These results suggest that virtual reality could provide a novel mechanism-driven analgesic strategy in patients with altered central pain processing.

Conditioned Pain Modulation (CPM) Effects Captured in Facial Expressions

Purpose

Conditioned pain modulation (CPM) is most often assessed using self-report of pain. However, self-report of pain is not always available (eg in individuals with cognitive impairment) and is susceptible to report bias. In comparison, the facial expression of pain is more reflex-like and represents one of the most sensitive and specific non-verbal signals of pain. The aim of the present study was to investigate whether the facial expression of pain is sensitive enough to capture endogenous pain inhibition as elicited during CPM paradigms.

Patients and Methods

In total, 26 female participants took part in this study. Facial and verbal responses to phasic heat pain were assessed once while participants immersed their hand in a hot water bath and once without additional stimulation. Facial responses were analyzed using the Facial Action Coding System (FACS). Verbal responses were assessed using a Numerical Rating Scale (NRS).

Results

Pain-relevant facial responses as well as pain ratings to phasic heat pain were significantly reduced when participants simultaneously immersed their hand in a hot water bath compared to baseline. Thus, CPM effects could be demonstrated both on subjective as well as on facial responses. Moreover, CPM-induced changes in pain-relevant facial responses and in NRS ratings were significantly correlated.

Conclusion

The present study shows that facial expressions of pain are sensitive enough to capture CPM effects. Given the proven clinical usefulness of assessing CPM, the parallel assessment of verbal and facial CPM effects might be a promising approach with wider scope of applications. Further research in other demographic healthy participant and clinical cohorts is warranted.

Development and Validation of a Predictive Model of Pain Modulation Profile to Guide Chronic Pain Treatment: A Study Protocol

Introduction: Quantitative sensory testing is frequently used in research to assess endogenous pain modulation mechanisms, such as Temporal Summation (TS) and Conditioned Pain Modulation (CPM), reflecting excitatory and inhibitory mechanisms, respectively. Numerous studies found that a dysregulation of these mechanisms is associated with chronic pain conditions. In turn, such a patient's “profile” (increased TS and/or weakened CPM) could be used to recommend different pharmacological treatments. However, the procedure to evaluate these mechanisms is time-consuming and requires expensive equipment that is not available in the clinical setting. In this study, we aim to identify psychological, physiological and socio-demographic markers that could serve as proxies to allow healthcare professionals to identify these pain phenotypes in clinic, and consequently optimize pharmacological treatments.

Method: We aim to recruit a healthy participant cohort (n = 360) and a chronic pain patient cohort (n = 108). Independent variables will include psychological questionnaires, pain measurements, physiological measures and sociodemographic characteristics. Dependent variables will include TS and CPM, which will be measured using quantitative sensory testing in a single session. We will evaluate one prediction model and two validation models (for healthy and chronic pain participants) using multiple regression analysis between TS/CPM and our independent variables. The significance thresholds will be set at p = 0.05, respectively.

Perspectives: This study will allow us to develop a predictive model to compute the pain modulation profile of individual patients based on their biopsychosocial characteristics. The development of the predictive model is the first step toward the overarching goal of providing clinicians with a set of quick and cheap tests, easily applicable in clinical practice to orient pharmacological treatments.

Effects of oral alcohol administration on heat pain threshold and ratings of supra-threshold stimuli

Background and aims Evidence for analgesic effects of oral alcohol consumption on heat pain has recently been documented in a placebo-controlled, randomized and double-blind design. We aimed at further investigating these effects and now set the focus on pain threshold and the ratings of supra-threshold pain to cover most of the pain range. Moreover, we now firstly evaluated sex differences in these effects. Methods We investigated 41 healthy participants (22 females) in a randomized, double-blind and placebo-controlled design and targeted two different moderate breath-alcohol levels of 0.06% and 0.08%. Before and after an alcoholic or placebo drink, contact heat was applied at the forearm. Subjects evaluated pain threshold (method of adjustment) and rated pain intensity and pain unpleasantness of supra-threshold stimuli (intensity: threshold +3 °C; duration: 5 s). Results Analgesic effects taking the form of increased pain thresholds were found after both alcohol doses, surprisingly with more pronounced effects for the lower dose. While the high alcohol dose exerted small analgesic effects on pain intensity ratings (i.e. decrease), slightly increased ratings of pain intensity and pain unpleasantness after the low alcohol dose rather suggest pain enhancement. Alcohol did not affect intensity vs. unpleasantness ratings differentially. We found no evidence for sex differences in any of these effects. Conclusions Overall, acute alcohol effects on pain were subtle. Our findings suggest that while low alcohol doses already exert analgesic effects on pain threshold, stronger doses are required for pain reduction on supra-threshold pain levels. Furthermore, sex differences could not be detected within our experimental paradigm but should be further explored in future research. Implications Analgesic effects of sub-toxic alcohol doses - as normally occurring during social drinking - might be weak; however, susceptibility to pain relieving effects of alcohol might be a risk factor for the use of alcohol as self-medication in acute pain states.

What goes up must come down: insights from studies on descending controls acting on spinal pain processing

Descending controls link higher processing of noxious signals to modulation of spinal cord responses to their noxious inputs. It has become possible to study one key inhibitory system in animals and humans using one painful stimulus to attenuate another distant response and so eliciting diffuse noxious inhibitory controls (DNIC) or the human counterpart, conditioned pain modulation (CPM). Here, we discuss the neuronal pathways in both species, their pharmacology and examine changes in descending controls with a focus on osteoarthritis. We will also discuss the opposing descending facilitatory system. Strong parallels between DNIC and CPM emphasize the possibility of forward and reverse translation.