Pain perception to the cold pressor test during the menstrual cycle in relation to estrogen levels and a comparison with men

Ganoderma tsuage promotes pain sensitivity in aging mice

Advances in modern medicine have extended human life expectancy, leading to a world with a gradually aging society. Aging refers to a natural decline in the physiological functions of a species over time, such as reduced pain sensitivity and reaction speed. Healthy-level physiological pain serves as a warning signal to the body, helping to avoid noxious stimuli. Physiological pain sensitivity gradually decreases in the elderly, increasing the risk of injury. Therefore, geriatric health care receives growing attention, potentially improving the health status and life quality of the elderly, further reducing medical burden. Health food is a geriatric healthcare choice for the elderly with Ganoderma tsuage (GT), a Reishi type, as the main product in the market. GT contains polysaccharides, triterpenoids, adenosine, immunoregulatory proteins, and other components, including anticancer, blood sugar regulating, antioxidation, antibacterial, antivirus, and liver and stomach damage protective agents. However, its pain perception-related effects remain elusive. This study thus aimed at addressing whether GT could prevent pain sensitivity reduction in the elderly. We used a galactose-induced animal model for aging to evaluate whether GT could maintain pain sensitivity in aging mice undergoing formalin pain test, hot water test, and tail flexes. Our results demonstrated that GT significantly improved the sensitivity and reaction speed to pain in the hot water, hot plate, and formalin tests compared with the control. Therefore, our animal study positions GT as a promising compound for pain sensitivity maintenance during aging.

Symptoms, Lifetime Duration of Estrogen Exposure, and Ovarian Reserve Among Women Living With HIV: A Cross-Sectional Observational Study

ABSTRACT

This cross-sectional observational study examined associations among symptom burden, lifetime duration of estrogen exposure, and serum antimüllerian hormone (AMH) levels among women living with HIV (n = 98) using bivariate bias-corrected Pearson correlations and multiple correspondence analyses. The mostly Black (85.6%) sample of women, with a mean age of 50 years (SD 12.6 years), exhibited no significant reproductive history factors and symptom burden interrelationships or significant associations between lifetime duration of estrogen exposure and symptoms. Predictably, serum AMH levels were lower among older women; however, less predictable were its significant relationships with months living with HIV (r = -0.362), months on ART (r = -0.270), and CD4+ T-cell nadir (r = 0.347). Symptom-symptom relationships support a fatigue, pain, sleep, anxiety, and depression symptom cluster. The hypotheses were not supported by cross-sectional observation. Further studies should explore variation in relationships between HIV, estrogen exposure, ovarian reserve, and AMH levels over time.

Regular use of acupressure mats reduces perceived stress at subjective but not psychophysiological levels: Insights from a three-week relaxation training

Acupressure mats are promoted as stress management tools for easy and effective self-application, promising reduced stress and increased well-being. However, the scientific evidence for these effects is based on few experimental studies and lacks the examination of acupressure mats as a solitary relaxation tool. Our study aimed to examine which changes in stress and well-being can be expected from the use of acupressure mats by healthy young people on the subjective and psychophysiological level. Unexperienced participants practiced relaxation for three weeks either with an acupressure mat or without any tools (active control group [CG]). As a results, subjective well-being and stress decreased, while sleep quality and concentration endurance increased across groups. Blood pressure (BP), heart rate (HR), pain threshold and pain tolerance did not change significantly from pre- to post-training measurements. Most importantly, no significant differences were found between groups, indicating that training with an acupressure mat yielded no superior effects compared with an active control condition in healthy young students. As a conclusion, taking time to relax has some but limited beneficial effects on the subjective levels independent of the specific method for healthy students. Potential beneficial effects of acupressure mats might be bound to specific impairments, such as tension pain.

Menstrual migraine is caused by estrogen withdrawal: revisiting the evidence

OBJECTIVE

To explore and critically appraise the evidence supporting the role of estrogen withdrawal in menstrual migraine.

MAIN BODY

Menstrual migraine, impacting about 6% of reproductive-age women, manifests as migraine attacks closely related to the menstrual cycle. The estrogen withdrawal hypothesis posits that the premenstrual drop in estrogen levels serves as a trigger of migraine attacks. Despite its wide acceptance, the current body of evidence supporting this hypothesis remains limited, warranting further validation. Estrogen is believed to exert a modulatory effect on pain, particularly within the trigeminovascular system - the anatomic and physiologic substrate of migraine pathogenesis. Nevertheless, existing studies are limited by methodologic inconsistencies, small sample sizes, and variable case definitions, precluding definitive conclusions. To improve our understanding of menstrual migraine, future research should concentrate on untangling the intricate interplay between estrogen, the trigeminovascular system, and migraine itself. This necessitates the use of robust methods, larger sample sizes, and standardized case definitions to surmount the limitations encountered in previous investigations.

CONCLUSION

Further research is thus needed to ascertain the involvement of estrogen withdrawal in menstrual migraine and advance the development of effective management strategies to address unmet treatment needs.

No effect of cold pressor test-induced arousal on attentional benefits and costs in an endogenous spatial orienting paradigm

Previous studies have shown that arousal can influence hemispatial bias, suggesting that changes in arousal affect the neural networks involved in spatial attention control. The goal of the present study was to measure the effects of increased arousal on endogenous attentional orienting. We used a Spatial Orienting Paradigm to quantify attentional benefits and costs as measures of attentional orienting and re-orienting responses and exposed participants (N = 25; Experiment 1) to a bilateral feet Cold Pressor Test (CPT) to manipulate arousal. Increases in subjective distress ratings and blood pressure confirmed the effect of CPT on arousal. Although no overall effects of CPT on reaction times in the Spatial Orienting Paradigm were detected, an exploratory analysis of sex-specific effects revealed a left-lateralised decrease in benefits and increase in costs after CPT exposure in the male subsample (N = 11). To confirm these preliminary results, we repeated the experiment in a larger sample (N = 29, all male), but found no effect of CPT on orienting, with moderate to strong evidence in favour of a model excluding all (interaction) effects of CPT exposure (all BF_Incl < 0.3). Instead, our replicated results indicate that voluntary orienting is unaffected by CPT-induced increases of arousal. In the light of previous studies, and keeping in mind the interpretative challenges of null results, we discuss how and why our findings may be specific to endogenous as opposed to exogenous orienting and how arousal could possibly lead to the previously established effects on visuospatial bias without simultaneously affecting orienting and the underlying attention control networks.

The Effects of Morphine, Baclofen, and Buspirone Alone and in Combination on Schedule-Controlled Responding and Hot Plate Antinociception in Rats

Better therapeutic options are needed for pain. Baclofen, buspirone, and morphine are characterized as having analgesic properties. However, little is known about potential interactions between analgesic effects of these drugs when combined. Furthermore, it is not known if the magnitude of these potential interactions will be similar for all drug effects. Thus, we tested the effects of these drugs alone and in combination for their capacity to produce thermal antinociception and to decrease food-maintained responding. Four male and four female Sprague-Dawley rats responded for food under a fixed-ratio 10 schedule; afterward they were immediately placed on a 52°C hot plate. Morphine, baclofen, and buspirone were examined alone and in 1:1 combinations, based upon ED₅₀ values. Morphine and baclofen effects were evaluated with the opioid antagonist naltrexone and the GABA_B antagonist (3-Aminopropyl)(diethoxymethyl)phosphinic acid (CGP35348), respectively. Morphine, baclofen, and buspirone dose dependently decreased operant responding, with the calculated ED₅₀ values being 7.09, 3.42, and 0.57 mg/kg, respectively. The respective antinociception ED₅₀ values were 16.15, 8.75, and 2.20 mg/kg. Analysis of 1:1 combinations showed the effects of morphine plus baclofen to decrease schedule-controlled responding and to produce thermal antinociception were synergistic. Effects of morphine plus buspirone and baclofen plus buspirone to decrease schedule-controlled responding were additive. Effects of the two combinations to produce thermal antinociception were synergistic. Naltrexone and CGP35348 antagonized the effects of morphine and baclofen, respectively. Synergistic antinociceptive effects, in conjunction with additive effects on food-maintained responding, highlight the therapeutic utility of opioid and non-opioid drug combinations.

Oral contraceptive use and its association with symptomatology in migraine patients

Background:

Hormonal changes in natural menstrual cycles are known to modulate and even worsen headache symptoms in migraineurs; however, the impact of oral contraceptive pills (OCP), including combined oral contraceptive (COC) and progestogen-only pills on migraine symptomatology, is little investigated.

Method:

In this retrospective cohort study of 1758 migraine patients, data from 1032 female patients aged 15–45 years were accessed and their contraceptive methods, if any, were analyzed. Further comparisons were conducted between patients with OCP use and those without OCP use regarding the demographics, headache symptoms, and associated symptoms. Most OCP users in this study were assumed to have used COC, but information of individual hormone content of OCP was not collected. Patients with nonoral hormonal contraceptives were excluded for further comparison.

Results:

The use of OCP was common (47.8%) among the study cohort. Compared to those without OCP use ( n = 410), patients with OCP use ( n = 493) were younger (27.4 ± 7.0 vs. 32.8 ± 7.9, p < 0.001), had lower headache frequency (days per month, 11.1 ± 7.5 vs. 12.3 ± 8.8, p = 0.03), were less likely to have osmophobia (47.3 vs. 54.4%, p = 0.033) or cranial autonomic symptoms (44.8 vs. 53.2%, p = 0.013), and more commonly reported menstrually-related worsening of headache (52.3 vs. 42.4%, p = 0.012). The proportion of migraine with aura or other headache characteristics including severity, unilaterality, and pulsatile characteristic showed no differences between groups.

Conclusion:

Our data provide real-life information about contraceptive use among patients with migraine. The use of OCP is associated with differences in migraine symptomatology. Further studies are needed to determine whether this relationship is causal and any possible underlying mechanism.

An Investigation of the Effects of Testosterone and Behavioral Expressions of Pain on Sex/Gender Differences in Pain Perception

Research indicates that women are more susceptible to pain than men, but the reason for this difference is unclear. While estrogen and progesterone have been implicated, testosterone has not received adequate consideration in the literature. Additionally, incorporating behavioral expressions, or exaggerations, of pain as an important aspect of pain perception is receiving increasing attention. The current study examined the role of testosterone in female pain expression and perception via the cold pressor test. Following all participant exclusions, 46 healthy participants (32 women) provided saliva samples for testosterone analysis using enzyme-linked immunosorbent assay before and after rating their pain during the cold pressor test. Participants used a visual analog scale to indicate how the 2℃ water was perceived, ranging from “worst pain imaginable” to “no pain.” The researcher also noted whether a participant displayed overt behavioral expressions of pain such as jumping and cursing. The results revealed that men reported lower visual analog scale scores than women, indicating less perceived pain. A subgroup of women who displayed overt behavioral responses to pain seemed to be driving this sex/gender difference. It was expected that this subgroup of females would have corresponding changes in testosterone that would further explain the observed sex/gender differences, but this was not supported. Collectively, these data add to the previous literature investigating sex/gender differences in pain perception and highlight the importance of studying overt behavioral expressions of pain. Testosterone may alter this behavior and subsequent pain perception, but the contributions of testosterone are likely subtle and were not detected in this study.

Enhancing Placebo Effects in Somatic Symptoms Through Oxytocin

OBJECTIVE

Placebo effects relieve various somatic symptoms, but it is unclear how they can be enhanced to maximize positive treatment outcomes. Oxytocin administration may potentially enhance placebo effects, but few studies have been performed, and they have had conflicting findings. The study aim was to investigate the influence of positive verbal suggestions and oxytocin on treatment expectations and placebo effects for pain and itch.

METHODS

One hundred eight female participants were allocated to one of the following four groups: (1) oxytocin with positive verbal suggestions, (2) placebo with positive verbal suggestions, (3) oxytocin without suggestions, and (4) placebo without suggestions. The administration of 24 IU oxytocin or a placebo spray was preceded by positive verbal suggestions regarding the pain- and itch-relieving properties of the spray or no suggestions, depending on group allocation. Pain was assessed with a cold pressor test, and itch was assessed with histamine iontophoresis.

RESULTS

Positive verbal suggestions induced expectations of lower pain (F = 4.77, p = .031) and itch (F = 5.38, p = .022). Moreover, positive verbal suggestions elicited placebo analgesia (F = 5.48, p = .021) but did not decrease itch. No effect of oxytocin on the placebo effect or on expectations was found.

CONCLUSIONS

Positive suggestions induced placebo analgesia but oxytocin did not enhance the placebo effect. Study limitations are that we only included a female sample and a failure to induce placebo effect for itch. Future studies should focus on how oxytocin might influence placebo effects, taken into account the role of sex, dose-dependent effects, and various expectation manipulations.

TRIAL REGISTRATION

The study was registered as a clinical trial on www.trialregister.nl (number 6376).

Effect of Age, Sex and Gender on Pain Sensitivity: A Narrative Review

Introduction:

An increasing body of literature on sex and gender differences in pain sensitivity has been accumulated in recent years. There is also evidence from epidemiological research that painful conditions are more prevalent in older people. The aim of this narrative review is to critically appraise the relevant literature investigating the presence of age and sex differences in clinical and experimental pain conditions.

Methods:

A scoping search of the literature identifying relevant peer reviewed articles was conducted on May 2016. Information and evidence from the key articles were narratively described and data was quantitatively synthesised to identify gaps of knowledge in the research literature concerning age and sex differences in pain responses.

Results:

This critical appraisal of the literature suggests that the results of the experimental and clinical studies regarding age and sex differences in pain contain some contradictions as far as age differences in pain are concerned. While data from the clinical studies are more consistent and seem to point towards the fact that chronic pain prevalence increases in the elderly findings from the experimental studies on the other hand were inconsistent, with pain threshold increasing with age in some studies and decreasing with age in others.

Conclusion:

There is a need for further research using the latest advanced quantitative sensory testing protocols to measure the function of small nerve fibres that are involved in nociception and pain sensitivity across the human life span.

Implications:

Findings from these studies should feed into and inform evidence emerging from other types of studies (e.g. brain imaging technique and psychometrics) suggesting that pain in the older humans may have unique characteristics that affect how old patients respond to intervention.

Effects of cold sensitivity in the extremities on circulating adiponectin levels and metabolic syndrome in women

Background

In adipose tissues, adipokine levels, including adiponectin and leptin, are involved in insulin sensitivity and are reciprocally induced by cold temperature stress. Thermogenic response in the extremities (hands and feet) against cold stress can be negatively related to fat mass accumulation, particularly in the abdomen. However, the relationship between the sensation of cold in the extremities and circulating levels of adipokines is not fully understood. Here, we investigated whether adipokine levels are associated with cold hypersensitivity in the hands and feet (CHHF), independent of body mass, and whether the CHHF is related to metabolic syndrome (MS).

Methods

Associations of the CHHF with serum levels of adipokines and MS risk were evaluated in 1021 Koreans (372 men and 649 women), using a linear regression model while controlling for thermogenic factors and a logistic regression model, respectively.

Results

The adiponectin levels were positively associated with the CHHF, particularly in women, irrespective of thermogenic factors, including body mass index (β = 1.23 μg/mL, 95% confidence interval [1.04–1.45]). Logistic regression analysis for MS risk via the CHHF showed that there was a significant inverse association in women (odds ratio = 0.449, 95% confidence interval [0.273–0.737]).

Conclusions

In summary, our founding indicated that the CHHF could induce increased levels of circulating adiponectin and in turn reduce the MS risk in women. Despite complaints of feeling cold, these women could be at lower risk of cardiovascular disease.

Beliefs About Pharmaceutical Medicines and Natural Remedies Explain Individual Variation in Placebo Analgesia

This study examined whether placebo responses were predicted by a theoretical model of specific and general treatment beliefs. Using a randomized crossover, experimental design (168 healthy individuals) we assessed whether responses to a cold pressor task were influenced by 2 placebo creams described as pharmaceutical versus natural. We assessed whether placebo responses were predicted by pretreatment beliefs about the treatments (placebo) and by beliefs about the pain. The efficacy of pharmaceutical as well as natural placebos in reducing pain intensity was predicted by aspects of pain catastrophizing including feelings of helplessness (pharmaceutical: B = .03, P < .01, natural: B = .02, P < .05) and magnification of pain (pharmaceutical: B = .04, P < .05, natural: B = .05, P < .05) but also by pretreatment necessity beliefs (pharmaceutical: B = .21, P < .01, natural: B = .16, P < .05) and, for the pharmaceutical condition, by more general beliefs about personal sensitivity to pharmaceuticals (B = .14, P < .05). Treatment necessity beliefs also partially mediated the effects of helplessness on placebo responses. Treatment necessity beliefs for the pharmaceutical placebo were influenced by general pharmaceutical beliefs whereas necessity beliefs for the natural placebo were informed by general background beliefs about holistic treatments. Our findings show that treatment beliefs influence the placebo effect suggesting that they may offer an additional approach for understanding the placebo effect.

PERSPECTIVE

Placebo effects contribute to responses to active analgesics. Understanding how beliefs about different types of treatment influence placebo analgesia may be useful in understanding variations in treatment response. Using the cold pressor paradigm we found that placebo analgesia was influenced by beliefs about natural remedies, pharmaceutical medicines, and about pain.

Functional near-infrared spectroscopy study on tonic pain activation by cold pressor test

Functional near-infrared spectroscopy (fNIRS) has recently been suggested for monitoring cortical hemodynamic response to experimental and clinical acute pain. However, the hemodynamic response to a tonic, noxious cold stimulus, and its relation with subjective pain sensation is not fully characterized. We investigated the relationship between pain threshold and tolerance and the evoked hemodynamic response to cold pressor tests (CPTs) at varying intensities and explored the gender effect. Twenty-one healthy individuals (10 males and 11 females) performed four CPTs at 1°C, 5°C, 10°C, and 15°C. Deoxyhemoglobin (HHb) and oxyhemoglobin ([Formula: see text]) were measured continuously on the forehead by two "far" and two "near" channels in addition to pain scores, threshold, and tolerance. We found a significant within-subject correlation between pain threshold and the immediate [Formula: see text] response at the right frontal region. Gender difference and asymmetrical activation were observed in the "far" channels but not the "near" channels, suggesting a hemispheric preference in response to noxious cold stimuli. No gender difference was found in pain threshold, tolerance, or scores. This research adds to the body of literature suggesting the use of fNIRS for bedside assessment of pain in addition to behavioral and subjective measures for comprehensive, multimodal pain management.

Potential neurobiological benefits of exercise in chronic pain and posttraumatic stress disorder: Pilot study

This pilot study assessed the effects of cardiopulmonary exercise testing and cardiorespiratory fitness on plasma neuropeptide Y (NPY), allopregnanolone and pregnanolone (ALLO), cortisol, and dehydroepiandrosterone (DHEA), and their association with pain sensitivity. Medication-free trauma-exposed participants were either healthy (n = 7) or experiencing comorbid chronic pain/posttraumatic stress disorder (PTSD) (n = 5). Peak oxygen consumption (VO2) during exercise testing was used to characterize cardiorespiratory fitness. Peak VO2 correlated with baseline and peak NPY levels (r = 0.66, p < 0.05 and r = 0.69, p < 0.05, respectively), as well as exercise-induced changes in ALLO (r = 0.89, p < 0.001) and peak ALLO levels (r = 0.71, p < 0.01). NPY levels at the peak of exercise correlated with pain threshold 30 min after exercise (r = 0.65, p < 0.05), while exercise-induced increases in ALLO correlated with pain tolerance 30 min after exercise (r = 0.64, p < 0.05). In contrast, exercise-induced changes in cortisol and DHEA levels were inversely correlated with pain tolerance after exercise (r = -0.69, p < 0.05 and r = -0.58, p < 0.05, respectively). These data suggest that cardiorespiratory fitness is associated with higher plasma NPY levels and increased ALLO responses to exercise, which in turn relate to pain sensitivity. Future work will examine whether progressive exercise training increases cardiorespiratory fitness in association with increases in NPY and ALLO and reductions in pain sensitivity in chronic pain patients with PTSD.

Cold pressor gel test: A safe alternative to the cold pressor test in fMRI

PURPOSE

This study describes a new methodology-the cold pressor gel test (CPGT)-for delivering an accessible experimental pain stimulus, which is reproducible and safe for functional MRI (fMRI).

METHODS

The cold pressor test was modified to put safety precautions into the CPGT. The material used is cool gelled water with a thickening product, which provides a stable temperature at 0.2 °C. Thirteen women with chronic pelvic pain were scanned using a 3 Tesla (T) MR scanner equipped with a 12-channel head coil. Changes in BOLD activation during cold-induced pain were estimated.

RESULTS

The results have demonstrated that gel substances maintain a stable temperature during the experiment, resulting in an insignificant variation. Before the experiment, the mean temperature was 0.2 ± 0.11 °C, and at the end it was 0.7 ± 0.15 °C. The time taken by participants to reach the maximum level of pain during the CPGT was 56.92 ± 11.09 s. The pain intensity during the experiments was 6.92 ± 1.66 on the visual analog scale (VAS). The fMRI analysis showed significant BOLD activation in the main brain regions involved in chronic pain processing.

CONCLUSION

The CPGT is an experimental tool to deliver pain that is easily reproducible, particularly in brain functional imaging studies. Moreover, it is cost-effective, safe, and compatible with fMRI. Magn Reson Med 78:1464-1468, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Actions, Intentions, and Self-Assessment: The Road to Self-Enhancement Is Paved with Good Intentions

Actions and intentions do not always align. Individuals often have good intentions that they fail to fulfill. The studies presented here suggest that actors and observers differ in the weight they assign to intentions when deciding whether an individual possesses a desirable trait. Participants were more likely to give themselves credit for their intentions than they were to give others credit for theirs (Studies 1 and 2). This caused individuals to evaluate themselves more favorably than they evaluated others (Studies 3-5). Discussion focuses on the motivational and information-processing roots of this actor-observer difference in the weight assigned to intentions as well as the implications of this tendency for everyday judgment and decision making.

Gender Differences in Pain-Physical Activity Linkages among Older Adults: Lessons Learned from Daily Life Approaches

Background. Many older adults know about the health benefits of an active lifestyle, but, frequently, pain prevents them from engaging in physical activity. The majority of older adults experience pain, a complex experience that can vary across time and is shaped by sociocultural factors like gender. Objectives. To describe the time-varying associations between daily pain and physical activity and to explore differences in these associations between women and men. Methods. One hundred and twenty-eight community-dwelling older adults aged 65 years and older were asked to report their pain levels three times daily over a 10-day period and wear an accelerometer to objectively capture their daily physical activity (step counts and minutes of moderate to vigorous physical activity). Results. Increased daily step counts and minutes of moderate to vigorous physical activity were associated with increased daily pain, especially among women. Confirming past literature and contrasting findings for daily pain reports, overall pain levels across the study period were negatively associated with minutes of moderate to vigorous physical activity. Conclusions. Findings highlight that pain is significantly associated with physical activity in old age. The nature of this association depends on the time scale that is considered and differs between women and men.

Amygdala functional connectivity is reduced after the cold pressor task

The amygdala forms a crucial link between central pain and stress systems. Previous research indicates that psychological stress affects amygdala activity, but it is less clear how painful stressors influence subsequent amygdala functional connectivity. In the present study, we used pulsed arterial spin labeling (PASL) to investigate differences in healthy male adults' resting-state amygdala functional connectivity following a cold pressor versus a control task, with the stressor and control conditions being conducted on different days. During the period of peak cortisol response to acute stress (approximately 15-30 min after stressor onset), participants were asked to rest for 6 min with their eyes closed during a PASL scanning sequence. The cold pressor task led to reduced resting-state functional connectivity between the amygdalae and orbitofrontal cortex (OFC) and ventromedial prefrontal cortex, and this occurred irrespective of cortisol release. The stressor also induced greater inverse connectivity between the left amygdala and dorsal anterior cingulate cortex (ACC), a brain region implicated in the down-regulation of amygdala responsivity. Furthermore, the degree of poststressor left amygdala decoupling with the lateral OFC varied according to self-reported pain intensity during the cold pressor task. These findings indicate that the cold pressor task alters amygdala interactions with prefrontal and ACC regions 15-30 min after the stressor, and that these altered functional connectivity patterns are related to pain perception rather than cortisol feedback.

Effects of cold-pressor and mental arithmetic on pupillary light reflex

Dynamic pupillary light reflex (PLR) is a simple neurological test that can be useful for assessment of autonomic disorders. In this study, we investigated the changes in PLR induced by mental arithmetic task and cold pressor trials which are often applied in research as model systems to elicit autonomic responses. PLR was recorded before, during and after mental arithmetic and cold pressor tasks in 20 healthy adults (ten males and ten females). Stress-induced sympathetic activation was evident as shown in the increased blood pressure during both tasks. Although the pupillary constriction amplitude did not show significant changes, both constriction time and redilation time changed during the tasks. A significant gender effect was observed in cold pressor that suggested more sympathetic activation in males and faster parasympathetic activation in females in response to light stimulation under cold pressor.

Comparing pain sensitivity and the nociceptive flexion reflex threshold across the mid-follicular and late-luteal menstrual phases in healthy women

OBJECTIVES

Understanding the relationship between the menstrual cycle and pain can contribute significantly to our knowledge of pain processing in women. Many early studies suggested that pain sensitivity was enhanced during the luteal phase of the menstrual cycle relative to the follicular phase; however, these studies were often limited by small sample sizes, lack of ovulation verification, focus on a single pain modality, inadequate assessment of menstrual cycle regularity, and low-powered statistical methods. The current study was designed to address these limitations and examine the difference in pain processing between the mid-follicular (days 5 to 8) and late-luteal (days 1 to 6 preceding menses) phases.

METHODS

Forty-one healthy, regularly cycling women attended testing sessions that measured pain sensitivity from mechanical pain threshold, electrocutaneous pain threshold/tolerance, and ischemia pain threshold/tolerance, as well as McGill Pain Questionnaire qsensory and affective ratings of electric and ischemic stimuli. Electrocutaneous stimulation was also used to assess nociceptive flexion reflex threshold, a physiological measure of spinal nociception.

RESULTS

When analyses were limited to data collected only in the targeted menstrual phases (N=30), results indicated no menstrual phase effect on any pain outcome (all P's>0.05), with the exception of lower electrocutaneous pain thresholds during the late-luteal phase. No outcomes differed by menstrual phase in the full sample (N=41). This indicates nociceptive responding varies little between the mid-follicular and late-luteal phases.

DISCUSSION

The present study suggests that experimental pain processing does not significantly differ between the mid-follicular and late-luteal phases of the menstrual cycle in healthy women. This implies hormonal variation across these 2 phases (ie, progesterone) has a minimal effect on subjective and physiological responses to pain.

The role of circulating sex hormones in menstrual cycle-dependent modulation of pain-related brain activation

Sex differences in pain sensitivity have been consistently found, but the basis for these differences is incompletely understood. The present study assessed how pain-related neural processing varies across the menstrual cycle in normally cycling, healthy women, and whether menstrual cycle effects are based on fluctuating sex hormone levels. Fifteen subjects participated in 4 test sessions during their menstrual, midfollicular, ovulatory, and midluteal phases. Brain activity was measured while nonpainful and painful stimuli were applied with a pressure algometer. Serum hormone levels confirmed that scans were performed at appropriate cycle phases in 14 subjects. No significant cycle phase differences were found for pain intensity or unpleasantness ratings of stimuli applied during functional magnetic resonance imaging scans. However, lower pressure pain thresholds were found for follicular compared with other phases. Pain-specific brain activation was found in several regions traditionally associated with pain processing, including the medial thalamus, anterior and middle insula, midcingulate, primary and secondary somatosensory cortices, cerebellum, and frontal regions. The inferior parietal lobule, occipital gyrus, cerebellum, and several frontal regions showed interaction effects between stimulus level and cycle phase, indicating differential processing of pain-related responses across menstrual cycle phases. Correlational analyses indicated that cycle-related changes in pain sensitivity measures and brain activation were only partly explained by varying sex hormone levels. These results show that pain-related cerebral activation varies significantly across the menstrual cycle, even when perceived pain intensity and unpleasantness remain constant. The involved brain regions suggest that cognitive pain or more general bodily awareness systems are most susceptible to menstrual cycle effects.

Influence of estrogen levels on thermal perception, pain thresholds, and pain tolerance: studies on women undergoing in vitro fertilization

We examined the relationship between estrogen and pain in women undergoing in vitro fertilization (IVF). Quantitative sensory tests (QST) were performed twice during the IVF-regimen: once during hormonal down-regulation and once during hormonal up-regulation. A group of healthy men and a group of women using monophasic contraceptives were also examined, to control for session-to-session effects. Among the women undergoing IVF, serum 17β-estradiol levels differed strongly between treatments as expected, and increased from 65.7 (SD = 26) pmol/L during the down-regulation phase, to 5,188 (SD = 2,524) pmol/L during the up-regulation phase. Significant outcomes in the QST were only seen for temperature perception thresholds (1.7 °C versus 2.2 °C; P = .003) and cold pain threshold (11.5 °C versus 14.5 °C; P = .04). A similar change in cold pain threshold was also seen in the 2 control groups, however, and statistical analysis suggested that this change was due to a session-to-session effect rather than being the result of hormonal modulation. Heat pain thresholds, heat tolerance, pressure pain thresholds, and the cold pressor test showed no significant differences between sessions. These data demonstrate that pain perception and pain thresholds in healthy women show little, if any, changes even with major variations in serum estradiol levels.

PERSPECTIVE

This study shows that pain perception and tolerance in women undergoing in vitro fertilization do not vary, despite the dramatic changes in 17β-estradiol levels induced by the treatment regimen. The result thus suggests that in humans, contrary to experimental animals, changes in estrogen levels have little influence on pain sensitivity.

A systematic literature review of 10 years of research on sex/gender and experimental pain perception - part 1: are there really differences between women and men?

The purpose of this systematic review was to summarize and critically appraise the results of 10 years of human laboratory research on pain and sex/gender. An electronic search strategy was designed by a medical librarian and conducted in multiple databases. A total of 172 articles published between 1998 and 2008 were retrieved, analyzed, and synthesized. The first set of results (122 articles), which is presented in this paper, examined sex difference in the perception of laboratory-induced thermal, pressure, ischemic, muscle, electrical, chemical, and visceral pain in healthy subjects. This review suggests that females (F) and males (M) have comparable thresholds for cold and ischemic pain, while pressure pain thresholds are lower in F than M. There is strong evidence that F tolerate less thermal (heat, cold) and pressure pain than M but it is not the case for tolerance to ischemic pain, which is comparable in both sexes. The majority of the studies that measured pain intensity and unpleasantness showed no sex difference in many pain modalities. In summary, 10 years of laboratory research have not been successful in producing a clear and consistent pattern of sex differences in human pain sensitivity, even with the use of deep, tonic, long-lasting stimuli, which are known to better mimic clinical pain. Whether laboratory studies in healthy subjects are the best paradigm to investigate sex differences in pain perception is open to question and should be discussed with a view to enhancing the clinical relevance of these experiments and developing new research avenues.

A systematic literature review of 10 years of research on sex/gender and pain perception - part 2: do biopsychosocial factors alter pain sensitivity differently in women and men?

This systematic review summarizes the results of 10 years of laboratory research on pain and sex/gender. An electronic search strategy was designed by a medical librarian to access multiple databases. A total of 172 articles published between 1998 and 2008 were retrieved, analyzed, and synthesized. The second set of results presented in this review (129 articles) examined various biopsychosocial factors that may contribute to differences in pain sensitivity between healthy women and men. The results revealed that the involvement of hormonal and physiological factors is either inconsistent or absent. Some studies suggest that temporal summation, allodynia, and secondary hyperalgesia may be more pronounced in women than in men. The evidence to support less efficient endogenous pain inhibitory systems in women is mixed and does not necessarily apply to all pain modalities. With regard to psychological factors, depression may not mediate sex differences in pain perception, while the role of anxiety is ambiguous. Cognitive and social factors appear to partly explain some sex-related differences. Finally, past individual history may be influential in female pain responses. However, these conclusions must be treated with much circumspection for various methodological reasons. Furthermore, some factors/mechanisms remain understudied in the field. There is also a need to assess and improve the ecological validity of findings from laboratory studies on healthy subjects, and perhaps a change of paradigm needs to be considered at this point in time to better understand the factors that influence the experience of women and men who suffer from acute or chronic pain.

Asians differ from non-Hispanic Whites in experimental pain sensitivity

This study examined differences between Asians and non-Hispanic Whites (Whites) in pain sensitivity, and its relationship to mean arterial pressure (MAP) and heart rate (HR). In 30 Whites (50% female) and 30 Asians (50% female), experimental pain sensitivity was assessed with a hand cold pressor task, yielding measures of pain threshold, tolerance, intensity, and unpleasantness. Mean arterial pressure and HR measurements taken at rest and in response to speech stress were assessed. Perceived stress, anxiety, perfectionism, parental criticism, parental expectations and depressive symptoms were also measured. The results indicated that for the cold pain test, Asians demonstrated significantly lower pain threshold and tolerance levels than Whites. Although no ethnic differences were seen for MAP or HR responses to stress, for Whites higher stress MAP levels were correlated with reduced pain sensitivity, while for Asians higher baseline and stress HR levels were correlated with reduced pain sensitivity. Asians reported higher parental expectations and greater parental criticism than Whites. For Asians only, higher levels of perfectionism were related to more depressive symptoms, anxiety and perceived stress. These results indicate that Asian Americans are more sensitive to experimental pain than Whites and suggest ethnic differences in endogenous pain regulatory mechanisms (e.g. MAP and HR). The results may also have implications for understanding ethnic differences in clinical pain.

Menstrual cycle effects on perceived exertion and pain during exercise among sedentary women

BACKGROUND

Increasing cardiovascular fitness through exercise participation among sedentary people is important for decreasing all-cause mortality. From an intervention perspective, identifying modifiable factors that maximize the successful initiation of exercise is of utmost importance. For women, cyclic hormonal variations can influence aspects of health and health behaviors, from smoking cessation efficacy to physiological responses to exercise. The purpose of this study was to examine the influence of menstrual cycle phase and hormonal contraceptive (HC) use on subjective response to an initial bout of moderate intensity exercise among previously sedentary women (n = 117).

METHODS

Women completed a treadmill exercise challenge session at 65% of their previously determined maximum oxygen consumption (Vo(2) max) during the early follicular, late follicular, or luteal phase. Participants reported ratings of perceived exertion and pain using Borg's Rating of Perceived Exertion (RPE) and CR10 scales at 10, 20, and 30 minutes during the exercise session.

RESULTS

There was a significant menstrual phase x birth control interaction on change in RPE [F(2, 111) = 3.75, p < 0.05] and change in perceived pain [F(2, 110) = 3.31, p < 0.05]. Women in the early follicular phase who were not using HCs had significantly greater increases in RPE and increases in pain compared with women in the late follicular and luteal phases.

CONCLUSIONS

Our results indicate that the use of HC and cycle phase influence sedentary women's subjective response to exercise. These results have important implications for the timing of exercise interventions aimed at increasing exercise among sedentary women.

Evaluation of potential sex differences in the subjective and analgesic effects of morphine in normal, healthy volunteers

RATIONALE

Sex differences in the analgesic effects of mu-opioid agonists have been documented extensively in rodents and, to a lesser extent, in non-human primates. To date, there have been few experimental studies investigating this effect in humans, and the conclusions have been equivocal.

OBJECTIVES

The aims of the present study were to examine potential sex differences in the analgesic, subjective, performance, and physiological effects of morphine in human research volunteers.

METHODS

Using a double-blind outpatient procedure, the present study investigated the effects of intramuscular morphine (0, 5, and 10 mg/70 kg, i.m.) in men (N = 8) and women (N = 10). The primary dependent measure was analgesia, as assessed by the cold pressor and mechanical pressure tests. Secondary dependent measures included subjective, performance, and physiological effects of morphine, as well as plasma levels of morphine.

RESULTS

No differences in the analgesic and performance effects of morphine were observed between men and women, but significant differences in morphine's subjective effects were found. Specifically, men reported greater positive effects, whereas women reported greater negative effects after morphine administration.

CONCLUSIONS

These data suggest that, in humans, there are sex differences in the subjective mood-altering effects of morphine but, based on this limited sample, there is little evidence for sex differences in its analgesic effects.

Menarche in girls and headache--a longitudinal analysis

BACKGROUND

Puberty is assumed to influence the occurrence of headache, increasing the risk for recurrent episodes, especially in girls. The increase of headache, in particular recurrent headache, in girls from around the age of 12 on, is often ascribed to the occurrence of menarche as the most stringent indicator of completed puberty.

OBJECTIVES

We examined the hypothesis that the occurrence of menarche in girls is predictive of recurrent headache in reference to no or rare headache in the past 6 months. Furthermore, the assumption was tested that headache episodes increase after onset of menarche but remain unchanged in girls not having experienced their first menstruation. We also expected a higher probability of migraine type of headache after menarche. In a further analysis girls with and without menarche were compared with boys, and a difference between gender only for girls with menarche was predicted.

METHODS

In an epidemiological study recruiting 8800 families with children 7-14 years in Southern Lower Saxony (Germany), we conducted 3 yearly panels based on postal questionnaires. Headache data are based on self-report of children from 9 years on. Parents were asked for information regarding the onset of menarche. Approximately 1100 girls and about the same number of boys constitute the sample for our analyses.

RESULTS

The results of a logistic regression analysis demonstrate that in 11- to 16-year-old girls having experienced menarche in either the year of the assessment of headache or 2 years before that, the risk for recurrent headache is increased when compared with girls without menarche. Intraindividual longitudinal analyses, however, do not support our hypotheses that after the onset of menarche headaches become more frequent. The expected differences in headache between girls with menarche and boys were found. The risk for migraine-like headaches is not significantly higher after onset of menarche than before.

CONCLUSIONS

Thus, results do not consistently support the hypothesis that puberty is a moderator of headache frequency. Even in cases where the outcome of regression analyses is supportive of our expectations, explained variance is diminutive (maximum 2.2%). Thus, the influence of menarche on headache seems to be only marginal.

Sex, gender, and pain: a review of recent clinical and experimental findings

Sex-related influences on pain and analgesia have become a topic of tremendous scientific and clinical interest, especially in the last 10 to 15 years. Members of our research group published reviews of this literature more than a decade ago, and the intervening time period has witnessed robust growth in research regarding sex, gender, and pain. Therefore, it seems timely to revisit this literature. Abundant evidence from recent epidemiologic studies clearly demonstrates that women are at substantially greater risk for many clinical pain conditions, and there is some suggestion that postoperative and procedural pain may be more severe among women than men. Consistent with our previous reviews, current human findings regarding sex differences in experimental pain indicate greater pain sensitivity among females compared with males for most pain modalities, including more recently implemented clinically relevant pain models such as temporal summation of pain and intramuscular injection of algesic substances. The evidence regarding sex differences in laboratory measures of endogenous pain modulation is mixed, as are findings from studies using functional brain imaging to ascertain sex differences in pain-related cerebral activation. Also inconsistent are findings regarding sex differences in responses to pharmacologic and non-pharmacologic pain treatments. The article concludes with a discussion of potential biopsychosocial mechanisms that may underlie sex differences in pain, and considerations for future research are discussed.

PERSPECTIVE

This article reviews the recent literature regarding sex, gender, and pain. The growing body of evidence that has accumulated in the past 10 to 15 years continues to indicate substantial sex differences in clinical and experimental pain responses, and some evidence suggests that pain treatment responses may differ for women versus men.