Pain perception in depression: relationships to symptomatology and naloxone-sensitive mechanisms

Effects of psychosocial stress and performance feedback on pain processing and its correlation with subjective and neuroendocrine parameters

OBJECTIVES

Previous research on stress-induced pain modulation suggests that moderate psychological stress usually leads to hyperalgesia while more severe threat results in hypoalgesia. However, existing studies often lack suitable control conditions imperative to identify mere stress effects. Similarly, research mainly focused on pure anticipation of a social threat, not taking into consideration actual experiences of social evaluation. Therefore, we set out to investigate actual social up- and downgrading combined with a standardized stress paradigm to evaluate short-term and prolonged changes in pain perception and their potential association with neuroendocrine and subjective stress parameters.

METHODS

We allocated 177 healthy women to four experimental conditions, either the standard version of the Trier Social Stress Test (TSST) followed by positive, negative or no performance feedback, or a well-matched but less demanding placebo version of the TSST. Stress responses were assessed with ratings, salivary alpha-amylase, and salivary cortisol. To capture putative effects of stress on pain, heat pain threshold, ratings of phasic heat pain stimuli, and conditioned pain modulation were measured.

RESULTS

Despite a largely successful stress induction, results do not support a reliable influence of experimentally induced social stress-with or without subsequent performance feedback-on pain in women. Further, we found no clear association of pain modulation and changes in neuroendocrine or subjective stress responses.

CONCLUSIONS

Our results contrast previous studies, which repeatedly demonstrated stress-induced hypo- or hyperalgesia. This might be due to methodological reasons as former research was often characterized by high heterogeneity regarding the applied stressors, low sample sizes, and lacking or inconclusive control conditions. Thus, our results raise the question whether pain modulation in women by experimental psychosocial stress might have been overestimated in the past. Future research is necessary, which should employ parametric stress induction methods including well-matched control tasks, taking into consideration the participants' gender/sex and the time course of the stress response relative to pain assessment. The study is registered as DRKS00026946 at 'Deutsches Register Klinischer Studien' (DRKS) and can be also found at the World Health Organization's search portal.

An assessment of sensory sensitivity in women suffering from depression using transcutaneous electrical nerve stimulation

Background

Perception is the process or result of the process arising from the mental interpretation of the phenomena occurring, therefore it depends not only on physiology, but is also psychologically and socially conditioned. The aim of this study was to assess if there is a difference in the sensory sensitivity to an electrical stimulus in women suffering from depression and what the hedonic rating is of the lived experience of transcutaneous electrical nerve stimulation.

Methods

The depression group: 44 women, who were inpatients treated for depression at the Psychiatric Ward in the Clinical Hospital, and the control group: 41 women, matched by the age, height and weight, with no mental illness. Measures: threshold for sensing current, type of sensation evoked, hedonic rating.

Results

Median sensing threshold of electric current (depression vs. control: 7.75 mA vs. 8.35 mA; no significant), type of sensation evoked (depression vs. control: tingling 90.9% vs. 92.7%, no significant), hedonic rating (depression vs. control: unpleasant 11.4% vs. 2.4%; p = 0.003), hedonic rating (mildly ill vs. moderately ill vs. markedly ill: unpleasant 5.3% vs. 6.3% vs. 33.3%; p = 0.066).

Conclusions

Women suffering from depression exhibit a similar threshold of sensitivity to an electrical stimulus as mentally healthy women, however the hedonic rating of the stimulus acting on the skin in the group of clinically depressed women was more negative than in the mentally healthy subjects. The stimulus was described as 'unpleasant' for many of the mentally unhealthy women. The most negative sensations related to the electrical stimulus were experienced by women with the highest severity of mental illness according to The Clinical Global Impression - Severity Scale.

The induction of social pessimism reduces pain responsiveness

OBJECTIVES

Past work has found that optimism reduces a person's responsiveness to pain, but the effects of pessimism are not clear. Therefore, we gave pessimistic forecasts of participants' future social life and measured changes in their pain responsiveness. In particular, some participants were told that they would end up alone in life.

METHODS

Seventy-five subjects were investigated in three conditions (negative forecast, positive forecast, no forecast) for changes in pain threshold and pain tolerance threshold. Pressure pain induction was accomplished by either human- or machine-driven algometers. A randomly assigned bogus forecast promising either a lonely or a socially satisfying future was ostensibly based on a personality questionnaire and an emotional dot-probe task. As potential covariates, questionnaires assessing dispositional optimism (LOT-R), pain catastrophizing (PCS), and self-esteem (SISE) were given.

RESULTS

Pain thresholds suggested a change toward unresponsiveness only in the negative forecast condition, with only small differences between the modes of pain induction (i.e., human or machine). The results for pain tolerance thresholds were less clear also because of limiting stimulation intensity for safety reasons. The covariates were not associated with these changes.

CONCLUSIONS

Thus, people expecting a lonely future became moderately less responsive to pain. This numbing effect was not modulated by personality measures, neither in a protective fashion via dispositional optimism and self-esteem nor in a risk-enhancing fashion via trait pain catastrophizing. Alternative mechanisms of action should be explored in future studies.

Altered physical pain processing in different psychiatric conditions

Several reports indicate either increased or decreased pain sensitivity associated with psychiatric disorders. Chronic pain is highly prevalent in many of these conditions. We reviewed the literature regarding experimental pain sensitivity in patients with major depression, bipolar disorder, posttraumatic stress disorder (PTSD), generalized anxiety disorder, panic disorder, obsessive-compulsive disorder and schizophrenia. Electronic searches were performed to identify studies comparing experimental pain in patients with these conditions and controls. Across 31 depression studies, reduced pain threshold was noted except for ischemic stimuli, where increased pain tolerance and elevated sensitivity to ischemic pain was observed. A more pervasive pattern of low pain sensitivity was found across 20 schizophrenia studies. The majority of PTSD studies (n = 20) showed no significant differences compared with controls. The limited number of bipolar disorder (n = 4) and anxiety (n = 9) studies precluded identification of clear trends. Wide data variability was observed. Awareness of psychiatric patients' pain perception abnormalities is needed for active screening and addressing physical comorbidities, in order to enhance quality of life, life expectancy and mental health.

Ondansetron Does Not Reduce Withdrawal in Patients With Physical Dependence on Chronic Opioid Therapy

OBJECTIVES

Individuals taking opioids for an extended period of time may become physically dependent, and will therefore experience opioid withdrawal should they stop taking the medication. Previous work in animal and human models has shown that the serotonin (5-HT3) receptor may be implicated in opioid withdrawal. In this study, we investigated if ondansetron, a 5-HT3-receptor antagonist, could reduce the symptoms of opioid withdrawal after chronic opioid exposure in humans.

METHODS

In this double-blinded, randomized, crossover study, 33 chronic back pain patients (N = 33) were titrated onto sustained-release oral morphine for 30 days. After titration, participants attended 2 study sessions, 1 week apart, in which opioid withdrawal was induced with intravenous naloxone, with or without 8 mg intravenous ondansetron pretreatment. Opioid withdrawal symptoms were assessed by a blinded research assistant (objective opioid withdrawal score [OOWS]) and by the research participant (subjective opioid withdrawal score [SOWS]).

RESULTS

Clinically significant signs of withdrawal were observed during both the ondansetron (ΔOOWS = 3.58 ± 2.22, P < 0.0001; ΔSOWS = 12.48 ± 11.18, P < 0.0001) and placebo sessions (ΔOOWS = 3.55 ± 2.39, P < 0.0001; ΔSOWS = 12.21 ± 10.72, P < 0.0001), but no significant differences were seen between the treatment sessions in either the OOWS or SOWS scores.

CONCLUSION

We hypothesized that ondansetron would reduce opioid withdrawal symptoms in human subjects, but found no difference in withdrawal severity between ondansetron and placebo sessions. These findings suggest that more investigation may be necessary to determine if 5-HT3-receptor antagonists are suitable treatment options for opioid withdrawal.

Impaired Spinal Glucocorticoid Receptor Signaling Contributes to the Attenuating Effect of Depression on Mechanical Allodynia and Thermal Hyperalgesia in Rats with Neuropathic Pain

Although depression-induced altered pain perception has been described in several laboratory and clinical studies, its neurobiological mechanism in the central nervous system (CNS), particularly in the spinal dorsal horn, remains unclear. Therefore, in this study, we aimed to clarify whether nociceptive sensitivity of neuropathic pain is altered in the olfactory bulbectomy (OB) model of depression and whether glucocorticoid receptor (GR), which is involved in the etio-pathologic mechanisms of both major depression and neuropathic pain, contributes to these processes in the spinal dorsal horn of male Sprague-Dawley rats. The results showed that mechanical allodynia and thermal hyperalgesia induced by spinal nerve ligation (SNL) were attenuated in OB-SNL rats with decreased spinal GR expression and nuclear translocation, whereas non-olfactory bulbectomy (NOB)-SNL rats showed increased spinal GR nuclear translocation. In addition, decreased GR nuclear translocation with normal mechanical nociception and hypoalgesia of thermal nociception were observed in OB-Sham rats. Intrathecal injection (i.t.) of GR agonist dexamethasone (Dex; 4 μg/rat/day for 1 week) eliminated the attenuating effect of depression on nociceptive hypersensitivity in OB-SNL rats and aggravated neuropathic pain in NOB-SNL rats, which was associated with the up-regulation of brain-derived neurotrophic factor (BDNF), TrkB and NR2B expression in the spinal dorsal horn. The present study shows that depression attenuates the mechanical allodynia and thermal hyperalgesia of neuropathic pain and suggests that altered spinal GR-BDNF-TrkB signaling may be one of the reasons for depression-induced hypoalgesia.

Twice the negativity bias and half the positivity offset: Evaluative responses to emotional information in depression

BACKGROUND AND OBJECTIVES

Humans have the dual capacity to assign a slightly pleasant valence to neutral stimuli (the positivity offset) to encourage approach behaviors, as well as to assign a higher negative valence to unpleasant images relative to the positive valence to equally arousing and extreme pleasant images (the negativity bias) to facilitate defensive strategies. We conducted an experimental psychopathology study to examine the extent to which the negativity bias and the positivity offset differ in participants with and without major depression..

METHOD

Forty-one depressed and thirty-six healthy participants were evaluated using a structured clinical interview for DSM-IV Axis I disorders, questionnaires, and a computerized task designed to measure implicit affective responses to unpleasant, neutral, and pleasant stimuli.

RESULTS

The negativity bias was significantly higher and the positivity offset was significantly lower in depressed relative to healthy participants..

LIMITATIONS

Entry criteria enrolling medication-free participants with minimal DSM-IV comorbidity may limit generalizability of the findings.

CONCLUSIONS

This study advances our understanding of the positive and negative valence systems in depression, highlighting the irregularities in the positive valence system..

Is Pain Perception Altered in People With Depression? A Systematic Review and Meta-Analysis of Experimental Pain Research

Although clinical studies suggest depressed patients may be more vulnerable to pain, experimental research is equivocal. This meta-analysis aimed to clarify whether depression is associated with altered pain perception in response to noxious stimulation and to identify factors that might influence this association. A search of major electronic databases was conducted to identify experimental studies investigating pain response in depressed participants versus healthy control participants using established pain outcome measures. Random effects meta-analysis of standardized mean differences was conducted on data from 32 studies (N = 1,317). For high-intensity noxious stimulation, overall pain tolerance was similar across depressed and control groups (Hedges g = .09, P = .71, studies = 10). For low-intensity stimulation, a small, but statistically significant higher mean sensory threshold (g = .35, P = .01, studies = 9) and pain threshold (g = .32, P = .02, studies = 25) was observed in depressed participants, suggesting diminished pain. However, considerable heterogeneity in the direction and magnitude of effects was observed, indicating a likely condition-specific effect of depression on pain. Subgroup analysis found that pain threshold/tolerance was increased in depression for exteroceptive (cutaneous) stimulation but decreased for interoceptive (ischemic) stimulation, but that substantial heterogeneity remained. Overall, results provide some support for altered pain processing in depression, but suggest this link is dependent upon modality and additional, unidentified factors.

PERSPECTIVE

This meta-analysis of experimental studies suggests potential effects of depression on pain perception are variable and likely to depend upon multiple factors. The contrasting pattern for ischemic versus other noxious stimuli suggests that stimulus modality is a key factor, which could help explain discrepancies across clinical and experimental findings.

Who is healthy? Aspects to consider when including healthy volunteers in QST--based studies-a consensus statement by the EUROPAIN and NEUROPAIN consortia

Clinical and human experimental pain studies often include so-called "healthy" controls in investigations of sensory abnormalities, using quantitative sensory testing (QST) as an outcome measure. However, the criteria for what is considered "healthy" vary among the different studies and between study centers and investigators, partly explaining the high variability of the results. Therefore, several aspects should be considered during inclusion of healthy volunteers in QST-based trials to have homogenous groups of healthy controls with less variability between human experimental studies, so that results are less likely to be false negative or false positive because of subject-related factors. The EUROPAIN and NEUROPAIN consortia aimed to define factors influencing the variability in selection of healthy subjects in QST-based studies before the start of both projects and to give recommendations how to minimize it based on the current literature and expertise of the participants. The present suggestions for inclusion criteria of healthy volunteers into QST-based trials describe a 2-level approach including standardized questionnaires enabling the collection of relevant information on sociodemographic data, medical history, current health status, coping strategies in dealing with pain, and the motivation of the volunteer to participate in the study. These suggestions are believed to help researchers interpret their results in comparison with others and improve the quality of clinical studies including healthy volunteers as controls or in human experimental pain studies. They aim to reduce any confounding factors. Furthermore, the acquired information will allow post hoc analyses of variance for different potential influencing factors.

Experimental pain sensitivity in subjects with major depression: Many pain complaints without hypersensitivity

OBJECTIVE

Patients with major depression frequently complain of pain, but conflicting data exist concerning their changes in pain sensitivity. This study aimed at comparing the sensitivity to moderate controlled pain between subjects presenting a major depressive episode (isolated and recurrent depressive episodes or a bipolar disorder), controls, and subjects with schizophrenia from a previous study.

METHOD

Pain sensitivity was assessed obtaining the visual analog scale (VAS) rating for the application of a 160 kPa pre-fixed pressure (fpVAS), the pressure corresponding to a VAS score of 3, and the time required to achieve a VAS score of 3 during ischemia induction. The effects of depression intensity, alexithymia, current and past general pain, and of six weeks of antidepressant treatment on fpVAS were investigated.

RESULTS

The results did not differ significantly between the depressed groups and the controls, without any effect of depression intensity. Presence of long-lasting pain and current pain felt on the day of testing correlated with fpVAS. The subjects of the depressed group were less sensitive than subjects with schizophrenia. FpVAS was significantly lower before and after antidepressant treatment in the subjects presenting clinical improvement.

CONCLUSIONS

No difference in experimental pain sensitivity and expression between major depressive episode subjects and controls, in opposite to pain complaints, is to be detected. The changes in the sensation of pain routinely attributed to subjects presenting depression may result from changes in a differential processing of pain signals, not in relation with the depression intensity, or the kind of depressive disorder.

Sex differences in experimental measures of pain sensitivity and endogenous pain inhibition

It has been suggested that increased pain sensitivity and disruption of endogenous pain inhibitory processes may account, at least in part, for the greater prevalence and severity of chronic pain in women compared to men. However, previous studies addressing this topic have produced mixed findings. This study examined sex differences in pain sensitivity and inhibition using quantitative sensory testing (QST), while also considering the influence of other important factors such as depressive symptoms and sleep quality. Healthy men (n=24) and women (n=24) each completed a QST battery. This battery included an ischemic pain task (IPT) that used a submaximal effort tourniquet procedure as well as a conditioned pain modulation (CPM) procedure for the assessment of endogenous pain inhibition. Prior to QST, participants completed the Center for Epidemiologic Studies Depression Scale and the Pittsburgh Sleep Quality Index. Analyses revealed significant sex differences for the ischemic pain task and the conditioned pain modulation procedure, such that women tolerated the ischemic pain for a shorter amount of time and demonstrated less pain inhibition compared with men. This remained true even when accounting for sex differences in depressive symptoms and sleep quality. The results of this study suggest that women may be more pain sensitive and possess less-efficient endogenous pain inhibitory capacity compared with men. Whether interventions that decrease pain sensitivity and enhance pain inhibition in women ultimately improve their clinical pain outcomes is an area of research that deserves additional attention in the future.

Endogenous opioid antagonism in physiological experimental pain models: a systematic review

Opioid antagonists are pharmacological tools applied as an indirect measure to detect activation of the endogenous opioid system (EOS) in experimental pain models. The objective of this systematic review was to examine the effect of mu-opioid-receptor (MOR) antagonists in placebo-controlled, double-blind studies using ʻinhibitoryʼ or ʻsensitizingʼ, physiological test paradigms in healthy human subjects. The databases PubMed and Embase were searched according to predefined criteria. Out of a total of 2,142 records, 63 studies (1,477 subjects [male/female ratio = 1.5]) were considered relevant. Twenty-five studies utilized ʻinhibitoryʼ test paradigms (ITP) and 38 studies utilized ʻsensitizingʼ test paradigms (STP). The ITP-studies were characterized as conditioning modulation models (22 studies) and repetitive transcranial magnetic stimulation models (rTMS; 3 studies), and, the STP-studies as secondary hyperalgesia models (6 studies), ʻpainʼ models (25 studies), summation models (2 studies), nociceptive reflex models (3 studies) and miscellaneous models (2 studies). A consistent reversal of analgesia by a MOR-antagonist was demonstrated in 10 of the 25 ITP-studies, including stress-induced analgesia and rTMS. In the remaining 14 conditioning modulation studies either absence of effects or ambiguous effects by MOR-antagonists, were observed. In the STP-studies, no effect of the opioid-blockade could be demonstrated in 5 out of 6 secondary hyperalgesia studies. The direction of MOR-antagonist dependent effects upon pain ratings, threshold assessments and somatosensory evoked potentials (SSEP), did not appear consistent in 28 out of 32 ʻpainʼ model studies. In conclusion, only in 2 experimental human pain models, i.e., stress-induced analgesia and rTMS, administration of MOR-antagonist demonstrated a consistent effect, presumably mediated by an EOS-dependent mechanisms of analgesia and hyperalgesia.

Depression: a decision-theoretic analysis

The manifold symptoms of depression are common and often transient features of healthy life that are likely to be adaptive in difficult circumstances. It is when these symptoms enter a seemingly self-propelling spiral that the maladaptive features of a disorder emerge. We examine this malignant transformation from the perspective of the computational neuroscience of decision making, investigating how dysfunction of the brain's mechanisms of evaluation might lie at its heart. We start by considering the behavioral implications of pessimistic evaluations of decision variables. We then provide a selective review of work suggesting how such pessimism might arise via specific failures of the mechanisms of evaluation or state estimation. Finally, we analyze ways that miscalibration between the subject and environment may be self-perpetuating. We employ the formal framework of Bayesian decision theory as a foundation for this study, showing how most of the problems arise from one of its broad algorithmic facets, namely model-based reasoning.

No effects of hydrocortisone and dexamethasone on pain sensitivity in healthy individuals

BACKGROUND

There is some evidence that stress-induced cortisol increase leads to a decrease in pain, while lowering cortisol levels enhances pain sensitivity, but no study has yet investigated both pharmacological enhancement and reduction of cortisol levels in the same individuals.

METHODS

Firstly, we tested in 16 healthy individuals whether the treatment with hydrocortisone and dexamethasone, respectively, results in altered pain thresholds. Secondly, we aimed to test whether hormone effects are different across the pain range by using ratings for pain stimuli with varying intensity; and thirdly, we tested whether cortisol levels influence the discrimination ability for painful stimuli.

RESULTS

Despite substantial effects of dexamethasone and hydrocortisone administration on cortisol levels, no effect of these drugs was seen in terms of pain sensitivity (pain threshold, pain rating, pain discrimination ability), although comprehensively examined. However, in the placebo condition, a significant negative correlation between cortisol and pain thresholds was seen. Similarly, there were also strong negative associations between cortisol levels in the placebo condition and pain thresholds after drug treatment (especially after hydrocortisone).

CONCLUSION

These findings suggest that short-term variations of cortisol do not influence pain sensitivity whereas, in general, high levels of cortisol are associated with increased pain sensitivity, at least for weak to moderate stimuli.

Bodily maps of emotions

Emotions are often felt in the body, and somatosensory feedback has been proposed to trigger conscious emotional experiences. Here we reveal maps of bodily sensations associated with different emotions using a unique topographical self-report method. In five experiments, participants (n = 701) were shown two silhouettes of bodies alongside emotional words, stories, movies, or facial expressions. They were asked to color the bodily regions whose activity they felt increasing or decreasing while viewing each stimulus. Different emotions were consistently associated with statistically separable bodily sensation maps across experiments. These maps were concordant across West European and East Asian samples. Statistical classifiers distinguished emotion-specific activation maps accurately, confirming independence of topographies across emotions. We propose that emotions are represented in the somatosensory system as culturally universal categorical somatotopic maps. Perception of these emotion-triggered bodily changes may play a key role in generating consciously felt emotions.

Brain-network mechanisms underlying the divergent effects of depression on spontaneous versus evoked pain in rats: a multiple single-unit study

Studies have reported divergent behavioral effects of depression on spontaneous vs. stimulus-evoked pain. However, the underlying neurobiological mechanisms are still unclear. The present study used a depression model of unpredictable chronic mild stress (UCMS) and pain models for spontaneous pain (i.e., the formalin test) and acute evoked pain (i.e., noxious thermal stimulation) in rats. The activity of neurons within thalamo-cortical circuits in the lateral and medial pain pathways was recorded by a multiple-channel recording technique, and behaviors were observed simultaneously. The results confirmed our previous findings that rats exposed to UCMS tended to exhibit decreased pain sensitivity to experimental stimuli but increased behavioral responses to ongoing pain. Based on the analysis of single-unit responses, the results demonstrated that the processing of spontaneous vs. evoked pain in a depressive-like state was altered in the opposite direction (activation vs. inhibition). The ensemble encoding analysis revealed that exposure to UCMS gave rise to enhanced inter-regional functional connectivity in spontaneous pain processing, but did not influence that of evoked pain. In addition, different brain activation patterns underlying the processing of spontaneous vs. evoked pain were observed. These findings revealed that the distinct response patterns of neurons within the pain-related brain circuits, especially in the affective pain pathway, mediate the divergent effects of depression on spontaneous vs. evoked pain. This is also the first report on the electrophysiology of depression models that provides direct evidence that the effect of depression on spontaneous and evoked pain may involve different brain mechanisms.

Altered neuropathic pain behaviour in a rat model of depression is associated with changes in inflammatory gene expression in the amygdala

The association between chronic pain and depression is widely recognized, the comorbidity of which leads to a heavier disease burden, increased disability and poor treatment response. This study examined nociceptive responding to mechanical and thermal stimuli prior to and following L5-L6 spinal nerve ligation (SNL), a model of neuropathic pain, in the olfactory bulbectomized (OB) rat model of depression. Associated changes in the expression of genes encoding for markers of glial activation and cytokines were subsequently examined in the amygdala, a key brain region for the modulation of emotion and pain. The OB rats exhibited mechanical and cold allodynia, but not heat hyperalgesia, when compared with sham-operated counterparts. Spinal nerve ligation induced characteristic mechanical and cold allodynia in the ipsilateral hindpaw of both sham and OB rats. The OB rats exhibited a reduced latency and number of responses to an innocuous cold stimulus following SNL, an effect positively correlated with interleukin (IL)-6 and IL-10 mRNA expression in the amygdala, respectively. Spinal nerve ligation reduced IL-6 and increased IL-10 expression in the amygdala of sham rats. The expression of CD11b (cluster of differentiation molecule 11b) and GFAP (glial fibrillary acidic protein), indicative of microglial and astrocyte activation, and IL-1β in the amygdala was enhanced in OB animals when compared with sham counterparts, an effect not observed following SNL. This study shows that neuropathic pain-related responding to an innocuous cold stimulus is altered in an animal model of depression, effects accompanied by changes in the expression of neuroinflammatory genes in the amygdala.

The influence of physical activity on pain thresholds in patients with depression and multiple somatoform symptoms

OBJECTIVES

Pain is a common symptom with high occurrence in somatoform syndromes and depressive disorders. Research in this area often focuses on experimental induction of pain and subsequent assessment of pain thresholds, ensuring repeatable stimuli of defined quality. Results on sensitivity to experimental pain in major depression are inconclusive, and data on pain thresholds in multiple somatoform symptoms are scarce. The goals of the present study were to differentiate between groups regarding the pressure pain thresholds, and to investigate the possible influence of physical activity on the pain thresholds in these groups. We postulate that physical fitness and physical activity influence pain thresholds in depression and persons with multiple somatoform symptoms.

METHODS

Thirty-eight persons with major depression, 26 persons with a minimum of 6 to 8 somatoform symptoms (somatoform symptom index 8, SSI-8), and 47 healthy participants participated in the study. Baseline values of pressure pain thresholds assessed at different sites of the body were compared with those after 1 week of increased and 1 week of reduced physical activity.

RESULTS

We used repeated measurement design (MANCOVA) and partial correlations for data analysis. Depressed participants reported lower pain thresholds compared with controls, and persons with SSI-8 showed intermediate thresholds. After 1 week of physical activity, participants reported higher pain thresholds. Men had higher pain thresholds following activity as compared with women. Participants who reported higher general fitness also showed higher pain thresholds. Sensitivity to pressure pain is associated with depression, but not with multiple somatoform symptoms.

DISCUSSION

Short low-graded exercise can have reducing effects on perception of pressure pain. Physical activity level is a relevant covariate when using pressure pain assessment. Reduced general fitness can partially account for lower pain thresholds in depression.

Depression, cytokines and experimental pain: evidence for sex-related association patterns

BACKGROUND

There is robust evidence that altered neural-immune interactions including increased levels of proinflammatory cytokines are involved in both the pathogenesis of depression and altered pain processing. Proinflammatory cytokines induce sickness behavior, a constellation of symptoms that bears a strong similarity to those of depression. A feature of sickness behavior is enhanced pain sensitivity and it has been suggested that proinflammatory cytokines interact with pain processing directly and via several neurobiological pathways. Previous research indicates that depression and pain are closely related. We investigated the association between proinflammatory cytokines and experimental pain in major depression.

METHODS

Psychopathological variables, pressure pain thresholds (PPT) and concentrations of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) were measured in 37 outpatients with major depression and 48 healthy controls.

RESULTS

Compared with controls, depressed patients exhibited significantly higher levels of TNF-α and significantly decreased PPT indicating enhanced pain sensitivity. The group differences were robust when adjusting for sex and body mass index, although sex was significantly related to PPT. No group difference was observed in IL-6. PPT correlated significantly with TNF-α in women but not in men.

LIMITATIONS

Because of the cross-sectional design, causality of the relation between TNF-α and pain cannot be determined. Results should be considered preliminary given the small sample size.

CONCLUSION

The present findings suggest that increased pain sensitivity in depression may be linked to increased TNF-α concentration. The absence of this association in men is discussed in terms of pain-related psychobiological sex differences.

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.

Pain, sensory function, and neurogenic inflammatory response in young women with low mood

OBJECTIVE

To determine the relationship of mood status to pain complaints, sensory function, neurogenic inflammatory response, and general health in young women.

METHODS

Ninety-three women aged 18-29 participated in the study and were categorized by SCL-90-R depression score into low-mood (n=21) and normal-mood (n=72) groups. All subjects were below the threshold for possible clinical depression.

RESULTS

Low mood was associated with decreased tactile sensitivity, reduced response to topical capsaicin, and increased complaints of back, joint, muscle, and visceral pain, but not headache, when compared to normal mood controls. Low mood was also associated with reported poorer health and physical functioning, increased psychopathology, and family history of mood problems.

CONCLUSION

These data show that even subclinical low mood is associated with marked alterations in health and psychophysiological function.

Assessing pain in depression: what do ratings on unidimensional pain scales really mean?

OBJECTIVE

The study aims to determine which dimensions of pain-somatosensory, affective, or evaluative-would predict unidimensional pain scores in patients with major depressive disorder (MDD); compare the results with findings in cancer and chronic musculoskeletal pain patients; and examine the relationship between pain complaints and psychopathology.

METHODS

This is a 3-month prospective, observational study. Ninety-one Chinese patients were enrolled during an acute episode of MDD. Multidimensional Affect and Pain Survey (MAPS) was used to assess the multidimensional aspects of pain. Unidimensional pain intensity was evaluated using verbal rating scale (VRS) and visual analog scale (VAS). Hamilton Rating Scale for Depression and Hospital Anxiety and Depression Scale were used to assess depressive and anxiety symptoms.

RESULTS

The VRS and VAS pain scores were more highly correlated with MAPS somatosensory supercluster than with Hamilton Rating Scale for Depression, Hospital Anxiety and Depression Scale, and MAPS emotional and well-being superclusters. Hierarchical regression analyses showed that unidimensional pain scores were predicted better by MAPS somatosensory than by emotional clusters. The explained variance of VRS and VAS scores could be improved by 9% to 16% by adding somatosensory clusters after controlling for emotional clusters, whereas 1% to 4% of the variance was improved by adding emotional clusters after controlling for somatosensory clusters. Pain intensity was more closely related to anxiety symptoms than to depressive symptoms cross-sectionally and longitudinally.

CONCLUSION

Our data suggest that pain and emotional symptoms in MDD are not entirely related. In cases in which pain symptoms are severe or remain persistent despite treatment of depression, specific strategy targeting pain may be needed.

Pseudohypoalgesia on the skin: a novel view on the paradox of pain perception in depression

Previous studies reported increased heat pain thresholds and decreased ischemic pain thresholds in patients experiencing depression. The increased sensitivity to ischemic muscle pain was assumed to represent a model for the investigation of physical symptoms in the disease. Here, we explored how the serotonin and noradrenaline reuptake inhibitor duloxetine influences experimental pain thresholds and tolerances in depressed patients during treatment. Twenty-two patients experiencing unipolar depression were included. Pain assessments were conducted unmedicated at baseline, after 1 week, and after 6 weeks of duloxetine treatment. We observed the expected clinical response of patients indicated by a significant reduction in the Montgomery Depression Rating Scale after 6 weeks. At baseline, we found increased heat pain thresholds in patients in comparison to controls while patients simultaneously rated augmented pain perception on the visual analog scale. In contrast, patients were significantly more perceptive to ischemic muscle pain at baseline. During treatment, the examined pain thresholds showed differential changes: Increased heat pain thresholds of patients normalized during treatment, whereas no significant change was observed for ischemic pain thresholds. Thus, our results might change the view on the paradox of pain perception in major depression because increased heat pain thresholds are associated with augmented pain perception in the disease.

Effects of duloxetine treatment on brain response to painful stimulation in major depressive disorder

Major depressive disorder (MDD) is characterized by a constellation of affective, cognitive, and somatic symptoms associated with functional abnormalities in relevant brain systems. Painful stimuli are primarily stressful and can trigger consistent responses in brain regions highly overlapping with the regions altered in MDD patients. Duloxetine has proven to be effective in treating both core emotional symptoms and somatic complaints in depression. This study aimed to assess the effects of duloxetine treatment on brain response to painful stimulation in MDD patients. A total of 13 patients and a reference group of 20 healthy subjects were assessed on three occasions (baseline, treatment week 1, and week 8) with functional magnetic resonance imaging (fMRI) during local application of painful heat stimulation. Treatment with duloxetine was associated with a significant reduction in brain responses to painful stimulation in MDD patients in regions generally showing abnormally enhanced activation at baseline. Clinical improvement was associated with pain-related activation reductions in the pregenual anterior cingulate cortex, right prefrontal cortex, and pons. Pontine changes were specifically related to clinical remission. Increased baseline activations in the right prefrontal cortex and reduced deactivations in the subgenual anterior cingulate cortex predicted treatment responders at week 8. This is the first fMRI study addressed to assess the effect of duloxetine in MDD. As a novel approach, the application of painful stimulation as a basic neural stressor proved to be effective in mapping brain response changes associated with antidepressant treatment and brain correlates of symptom improvement in regions of special relevance to MDD pathophysiology.

Increased thermal and mechanical nociceptive thresholds in rats with depressive-like behaviors

Clinical observations suggest that depressed patients were less sensitive to experimental pain than healthy subjects. However, few animal studies are reported concerning the association of depression and pain. The purpose of this study was to investigate the effects of unpredictable chronic mild stress (UCMS) induced depression on the perceived intensity of painful stimulation in rats. We measured the thermal and mechanical paw withdrawal thresholds (PWT) of normal and spinal nerve ligated (SNL) rats using hot plate test and von Frey test, respectively. The results showed that rats exposed to UCMS exhibited significantly higher thermal and mechanical pain thresholds in comparison to the non-depressed controls. In particular, the PWT of the SNL group was restored to nearly normal level after three weeks of UCMS, and even comparable to that of the control group. These results strongly suggest that the depressed subjects have decreased sensitivity to externally applied noxious stimulation, which is consistent with our previous findings.

Histories of major depression and premenstrual dysphoric disorder: Evidence for phenotypic differences

This study examined unique versus shared stress and pain-related phenotypes associated with premenstrual dysphoric disorder (PMDD) and prior major depressive disorder (MDD). Sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA)-axis measures were assessed at rest and during mental stress, as well as sensitivity to cold pressor and tourniquet ischemic pain tasks in four groups of women: (1) non-PMDD with no prior MDD (N=18); (2) non-PMDD with prior MDD (N=9); (3) PMDD with no prior MDD (N=17); (4) PMDD with prior MDD (N=10). PMDD women showed blunted SNS responses to stress compared to non-PMDD women, irrespective of prior MDD; while women with prior MDD showed exaggerated diastolic blood pressure responses to stress versus never depressed women, irrespective of PMDD. However, only in women with histories of MDD did PMDD women have lower cortisol concentrations than non-PMDD women, and only in non-PMDD women was MDD associated with reduced cold pressor pain sensitivity. These results suggest both unique phenotypic differences between women with PMDD and those with a history of MDD, but also indicate that histories of MDD may have special relevance for PMDD.

Pain sensitivity in major depression and its relationship to central serotoninergic function as reflected by the neuroendocrine response to clomipramine

Several studies reported a decreased pain sensitivity in patients with depression, but the underlying neurobiological mechanisms of this phenomenon are unclear. While there is extensive evidence that the serotoninergic system plays a key role in pain modulation, especially in pain inhibitory mechanisms via descending pathways, as well as in the pathophysiology of depression, no study so far has examined its potential relevance in mediating the alteration of pain processing. The present study addresses the question of whether indices of serotoninergic dysfunction, as investigated by a neuroendrocine challenge paradigm, are related to pain sensitivity. Nineteen drug-free inpatients with unipolar major depression underwent a neuroendocrine challenge test by measuring cortisol and prolactin in response to intravenously administered clomipramine (12.5mg). Heat/cold pain thresholds, warmth/cold detection thresholds, measures of current pain complaints and mood were assessed the day before and three day after challenge procedure. When patients were classified in subgroups based on a median split of their cortisol response values, the low-responsive group showed significantly elevated heat pain thresholds and nearly significantly elevated cold pain thresholds compared to the high-responsive group. No such group differences were found with regard to somatosensory thresholds, measures of pain complaints and mood. Subgrouping on the basis of prolactin responsiveness did not reveal significant differences in any parameter. In summary, a decreased pain sensitivity was demonstrated in patients characterized by a reduced neuroendocrine responsiveness to clomipramine, suggesting an involvement of serotoninergic dysfunction underlying altered pain perception in depression.

Differential involvement of hippocampal vasoactive intestinal peptide in nociception of rats with a model of depression

The effects of VIP microinjected unilaterally (left or right) into the hippocampal CA1 area at a dose of 10 and 100 ng or bilaterally (10 ng), on nociception of male Wistar rats with a model of depression (bilateral olfactory bulbectomy-OBX) were studied. Nociception was examined applying mechanical pressure on the left hind paw of the rat (analgesy-meter test). It was found that in OBX rats the pain threshold is increased. VIP showed differential effects depending on the side and dose of administration. The pain threshold after left-side microinjections of VIP into the hippocampal CA1 area of OBX rats was significantly higher than that after injections into right-side. There are no significant differences between right-side VIP-treated and OBX rats. Bilateral microinjections of VIP also exerted antinociceptive effect. These findings suggest that the hippocampal lateralized antinociceptive effect of VIP in OBX rats depends on the hemisphere of injection and suggest that VIP-ergic neurons in the hippocampal CA1 area may play differential role in nociception of rats with a model of depression.

The influence of negative emotions on pain: behavioral effects and neural mechanisms

The idea that pain can lead to feelings of frustration, worry, anxiety and depression seems obvious, particularly if it is of a chronic nature. However, there is also evidence for the reverse causal relationship in which negative mood and emotion can lead to pain or exacerbate it. Here, we review findings from studies on the modulation of pain by experimentally induced mood changes and clinical mood disorders. We discuss possible neural mechanisms underlying this modulatory influence focusing on the periaqueductal grey (PAG), amygdala, anterior cingulate cortex (ACC) and anterior insula as key players in both, pain and affective processing.

Depression and changed pain perception: hints for a central disinhibition mechanism

Although patients with a depressive disorder report often of pain, their sensitivity to experimental pain is controversial, probably due to differences in sensory testing methods and to the lack of normal values. Therefore, we used a standardized and validated comprehensive sensory testing paradigm to assess the peripheral and central nervous system performance in depressive patients compared to healthy controls and chronic pain patients with fibromyalgia syndrome (FMS), in which depression is a common comorbidity. Twenty-five depressive psychiatric inpatients (pain-free: n=20), 35 FMS outpatients and 25 healthy controls underwent quantitative sensory testing (QST), including thermal and mechanical detection and pain thresholds, pain sensitivity and responsiveness to repetitive noxious mechanical stimuli (wind-up). In depressive disorder (to a lesser extent also in FMS), significantly decreased cold pain thresholds and an increased wind-up were found, although the mechanical pain thresholds and pain sensitivity were comparable to those of the healthy controls. All the detection thresholds were within the normal range in all the groups. In depressive disorder, there were no significant side differences in the detection and pain thresholds. The results contradict the former assumption of a general insensitivity to experimental pain in depressive disorder. In the mostly pain-free patients signs of an enhanced central hyperexcitability are even more pronounced than usually found in chronic pain patients (e.g. FMS), indicating common mechanisms in depressive disorder and chronic pain in accordance with the assumption of non-pain associated mechanisms in depressive disorder for central hyperexcitability, e.g. by inhibited serotonergic function. Furthermore, this trial demonstrates the feasibility of QST in depressive patients.

Depression augments activity-related pain in women but not in men with chronic musculoskeletal conditions

OBJECTIVES

The primary objective of the present study was to examine the role of sex as a moderator of the relation between depression and activity-related pain.

METHODS

The study sample consisted of 83 participants (42 women, 41 men) with musculoskeletal conditions. Participants were asked to lift a series of 18 canisters that varied in weight (2.9 kg, 3.4 kg and 3.9 kg) and distance from the body. Participants were asked to rate their pain while they lifted each canister and estimate the weight of the canisters.

RESULTS

Consistent with previous research, the relations among depression, pain intensity and disability were stronger for women than for men. ANOVA revealed that depression was associated with more intense activity-related pain in women only. For both women and men, the intensity of pain increased with each trial, although the weight of the objects lifted remained constant. Neither sex nor depression had an effect on participants' weight estimates.

CONCLUSIONS

The present discussion addresses the mechanisms through which depression may differentially affect pain in women and men. It also addresses the potential clinical implications of pain-augmenting effects of depression in women.

The relationship between fibromyalgia and major depressive disorder: a comprehensive review

OBJECTIVE

A large body of evidence suggests that the relationship between major depressive disorder (MDD) and fibromyalgia (FM) is complex. Improved understanding of this relationship promises to provide clinicians with better assessment and treatment options for both disorders.

METHOD

This paper reviews research on the prevalence, etiology and pathogenesis, clinical characterization, and treatment of FM and MDD, as well as studies that examined the relationship between these disorders. Studies were identified via PubMed literature search.

RESULTS

Our findings point to substantial similarities in neuroendocrine abnormalities, psychological characteristics, physical symptoms and treatments between FM and MDD. However, currently available findings do not support the assumption that MDD and FM refer to the same underlying construct or can be seen as subsidiaries of one disease concept.

CONCLUSION

New methodological and theoretical approaches may lead to a better understanding of the link between FM and MDD, and to more effective psychological and psychopharmacological therapies for FM patients. In the meantime, clinicians should carefully screen for a history of MDD in patients with FM.

Stress-evoked opioid release inhibits pain in major depressive disorder

To determine whether stress-evoked release of endogenous opioids might account for hypoalgesia in major depressive disorder (MDD), the mu-opioid antagonist naltrexone (50mg) or placebo was administered double-blind to 24 participants with MDD and to 31 non-depressed controls. Eighty minutes later participants completed a painful foot cold pressor test and, after a 5-min interval, began a 25-min arithmetic task interspersed with painful electric shocks. Ten minutes later participants completed a second cold pressor test. Negative affect was greater in participants with MDD than in non-depressed controls throughout the experiment, and increased significantly in both groups during mental arithmetic. Before the math task, naltrexone unmasked direct linear relationships between severity of depression, negative affect while resting quietly, and cold-induced pain in participants with MDD. In contrast, facilitatory effects of naltrexone on cold- and shock-induced pain were greatest in controls with the lowest depression scores. Naltrexone strengthened the relationship between negative affect and shock-induced pain during the math task, particularly in the depressed group, and heightened anxiety in both groups toward the end of the task. Thus, mu-opioid activity apparently masked a positive association between negative affect and pain in the most distressed participants. These findings suggest that psychological distress inhibits pain via stress-evoked release of opioid peptides in severe cases of MDD. In addition, tonic endogenous opioid neurotransmission could inhibit depressive symptoms and pain in people with low depression scores.

Cerebral blood flow changes associated with experimental pain stimulation in patients with major depression

BACKGROUND

The clinical relationship between pain and depression has been extensively reported. The purpose of this study was to compare the cerebral blood flow (CBF) of patients with major depressive disorder (MDD) during stimulation with experimental pain tolerance or sham stimulation, before and after 2 weeks of at least partially effective antidepressant treatment (ADT), in order to determine the cerebral regions associated with pain processing in the two clinical states.

METHODS

Twenty-four antidepressant-free outpatients diagnosed with MDD (DSM-IV), without any pain complaints and a basal score>or=20 points on the Hamilton Rating Scale for Depression were included. Cerebral SPECTs were performed before and after ADT. Patients were stimulated with pain pressure tolerance (PT) or sham stimulation during the radiotracer cerebral uptake time.

RESULTS

The comparison between PT and sham stimulation before ADT showed an increase of CBF of PT stimulated patients in right temporal gyrus, left amygdale, right anterior cingulated cortex, bilateral medial frontal gyrus, bilateral insula, lingual gyrus, right precentral gyrus and left postcentral gyrus. Equal comparison after ADT showed an increase of CBF of PT stimulated patients only in left middle frontal gyrus.

LIMITATIONS

The sample includes exclusively outpatients with mild-moderate depression.

CONCLUSION

CBF before ADT increases in brain areas related with the affective and cognitive components of pain; in contrast, after ADT increases only in cognitive pain related areas. These results offer new avenues to investigate the cerebral substrate of the common relationship between pain and depression.

Effects of total sleep deprivation in major depression: overnight improvement of mood is accompanied by increased pain sensitivity and augmented pain complaints

OBJECTIVE

Major depressive disorder (MDD) is associated with more pain complaints and an altered pain perception. Studies regarding the longitudinal relationship between depressive symptoms and pain processing have rarely been performed and have produced inconsistent results. To clarify how short-term alleviation of depressive mood is linked to changes in pain processing, the effect of sleep deprivation (SD) on pain and somatosensory thresholds, pain complaints, and mood was investigated in MDD patients.

METHODS

Nineteen drug-free inpatients with Diagnostic and Statistical Manual of Mental Disorders, fourth edition, diagnosis of MDD were investigated for 3 weeks. All patients received cognitive-behavioral therapy and were randomized to obtain either additional SD therapy (six nights of total SD, separated by recovery sleep) or no SD therapy (control group). Heat/cold pain thresholds, warmth/cold thresholds, measures of current pain complaints, and mood were assessed the evening before and the morning after SD as well as before and after a normal night sleep in the control group. Long-term changes of depressive symptomatology were assessed by weekly mood ratings.

RESULTS

Both treatment groups improved markedly in mood over the 3-week treatment period. SD regularly induced a moderate but statistically nonsignificant overnight improvement of mood, which was abolished by recovery sleep. Compared with the control condition, SD significantly decreased heat pain thresholds and nearly significantly cold pain thresholds; SD significantly augmented pain complaints the next morning. No such effects were observed for somatosensory thresholds.

CONCLUSIONS

SD induced differential short-term effects on mood and pain, with the patients being less depressed but more pain vulnerable.

Increased prefrontal activation during pain perception in major depression

BACKGROUND

To further elucidate the close interrelation of pain and depression, we investigated cerebral responses to parametrically varied thermal pain intensities in female patients suffering from major depressive disorder (MDD) (n = 13) and matched control subjects (n = 13) by means of functional magnetic resonance imaging (fMRI).

METHODS

After the assessment of the individual thermal pain threshold, an fMRI-compatible thermode was used to deliver thermal painful stimuli to the right arm. All stimuli were initiated for 10 sec from a baseline resting temperature (32 degrees C) in three different conditions (37 degrees C, 42 degrees C, 45 degrees C). Statistical Parametric Mapping 2 (SPM2) software was used for image processing and statistical analyses.

RESULTS

Patients displayed significantly increased thermal pain thresholds. A comparable increase in blood oxygenation level-dependent (BOLD) signal was observed in key structures of the pain matrix in patients and control subjects. Patients displayed hyperactivation in comparison with control subjects for the painful 45 degrees C condition in the left ventrolateral thalamus, in the right ventrolateral prefrontal cortex (VLPFC) and dorsolateral prefrontal cortex (DLPFC), as well as a stronger parametric BOLD signal increase in the right VLPFC, DLPFC, and in the contralateral insula. Symptom severity correlated positively with the BOLD signal in the left ventrolateral nucleus of the thalamus.

CONCLUSIONS

We present evidence that cortical structures of the pain matrix are similarly activated in depressed patients and healthy subjects. We report increased prefrontal and lateral thalamic activation during the presentation of painful stimuli, which might explain reduced thermal pain perception on the skin in depressed patients.

Is there a relationship between depression and crying? A review

OBJECTIVE

To conduct a systematic examination of the relationship between depression and crying by reviewing all relevant theory and empirical data including the performance of crying items in measures of depression.

METHOD

Review of the extant literature on depression and crying using PubMed, PsychInfo and Google Scholar databases.

RESULTS

Scores on crying items of depression inventories correlate moderately with overall depression severity. Otherwise, there is surprisingly little evidence for the widespread claim that depression leads to more frequent and/or easier crying. There is also little empirical support for the competing claim that severely depressed individuals lose their capacity to cry.

CONCLUSION

Current claims about the relationship between depression and crying lack a robust empirical foundation. Assessment instruments and diagnostic systems for mood disorders are inconsistent in how they handle crying as a symptom. Further work to investigate the causes and the context of crying in depressed patients is needed.

Central sensitization of the trigeminal and somatic nociceptive systems in medication overuse headache mainly involves cerebral supraspinal structures

Trigeminal and somatic nociceptive systems were studied in controls (n=15), episodic migraine (n=16), analgesics (n=14) and triptan-induced medication overuse headache (MOH) (n=15) before and after withdrawal. Patients with MOH and comorbid depressive symptoms and depression without headache were studied to investigate the influence of depression. Trigeminal nociception was studied by simultaneous registration of pain-related cortical potentials (PREP) and nociceptive blink reflex (nBR) following nociceptive-specific electrical stimulation of the forehead. Somatic nociception was evaluated using PREP of upper limbs. We found facilitation of both trigeminal and somatic PREP but not of nBR in MOH, which normalized after withdrawal. No differences were found comparing analgesics vs. triptan MOH. No differences were observed between controls and patients with episodic migraine and depression without headache. A transient facilitation was found of trigeminal and somatic nociceptive systems in MOH, which was more pronounced on a supraspinal level.

The Role of Mood States Underlying Sex Differences in the Perception and Tolerance of Pain

While sex differences in pain reporting are frequently observed, the reasons underlying these differences remain unclear. The present study examined sex differences in self-report and physiological measures of pain threshold and tolerance following the administration of two laboratory pain-induction tasks. The primary study aim centered on determining whether repeated exposure to such tasks would yield sex differences in terms of pain threshold and tolerance. In addition, it was hypothesized that if such differences did exist, negative mood states might account for changes in pain ratings, threshold, and/or tolerance in subsequent exposure to noxious stimuli. Recruited from a convenience sample, 66 participants (44 female and 22 male) were exposed to both thermal and cold noxious stimuli at three separate times, while psychophysiological and self-report data were collected. Because women outnumbered men 2:1, Fisher z transformations were performed to determine whether the observed associations between mood states and pain ratings differed. We found stronger associations between fatigue and thermal-heat pain ratings for men at their first and third exposure to the pain task compared to women (z = 2.11, P < 0.05; z = 3.14, P < 0.001, respectively). Results indicated that women evidenced greater pain tolerance than men on both a behavioral and physiological level; however, they reported greater pain severity than men. Fatigue was also found to be particularly important to reports of pain severity in men and pain tolerance in response to noxious stimuli for women. Possible pathways in which mood states influenced these endpoints are discussed.

Pain perception in major depression depends on pain modality

One frequently described feature of depression is an increased vulnerability to pain complaints, and chronic pain is frequently accompanied by symptoms of depression. In contrast to this, a decreased sensitivity to experimental pain has been described in major depression. The physiological basis of this phenomenon is yet elusive. We investigated 30 patients suffering from a major depressive disorder and matched controls. Pain testing (threshold and tolerance) was performed on both sides of the body and included assessment of thermal, electrical and ischemic pain. While confirming hypoalgesia to heat and electrical pain in comparison to controls, we found hyperalgesia to ischemic muscle pain. Furthermore, thermal pain tolerance and electrical pain tolerance were significantly increased on the right hand side confirming previous results of a lateralized perception of pain in depression. Our main finding suggests that painful stimuli are processed differentially depending on the localization of pain induction in depression. This knowledge may enable us to understand and ultimately treat pain complaints more appropriately in depressed patients.

Decreased sensitivity to experimental pain in adjustment disorder

An altered perception of pain has been described for several psychiatric disorders. To date the influence of adjustment disorders (AD) on pain perception has not been described. Here, we investigated perception of experimentally induced pain in 15 patients suffering from AD (subtype with depressive symptoms) and controls matched for age and sex. Thresholds and tolerances were assessed for thermal and electrical pain on both sides of the body. We found an overall increase of pain thresholds and tolerances in AD patients as compared to controls, predominately on the right side of the body. Analogue findings have been reported for pain perception in major depressive disorder (MDD). Of the data obtained, only thermal pain threshold on the right arm correlated with the severity of depressive symptoms. Although the underlying pathology is elusive it is likely that the mechanisms for reduced pain sensitivity are comparable in MDD and AD.