Sex differences in pain perception and cardiovascular responses in persons with parental history for hypertension

Chronic Pain-Associated Cardiovascular Disease: The Role of Sympathetic Nerve Activity

Chronic pain affects many people world-wide, and this number is continuously increasing. There is a clear link between chronic pain and the development of cardiovascular disease through activation of the sympathetic nervous system. The purpose of this review is to provide evidence from the literature that highlights the direct relationship between sympathetic nervous system dysfunction and chronic pain. We hypothesize that maladaptive changes within a common neural network regulating the sympathetic nervous system and pain perception contribute to sympathetic overactivation and cardiovascular disease in the setting of chronic pain. We review clinical evidence and highlight the basic neurocircuitry linking the sympathetic and nociceptive networks and the overlap between the neural networks controlling the two.

Effects of repeated exposures to experimental cold pain stimulus on pain perception in healthy young Indian men

Background

The influence of repeated exposures to cold pain stimulus, a surrogate of clinical pain, has remained largely unexplored. The study was planned to test the effect of repeated exposures to cold pain through cold pressor task on pain sensitivity and vascular reactivity.

Methods

Single-group experimental study. Thirty-seven healthy male volunteers (18-25 years) were exposed to cold pressor tasks for seven consecutive days and on the 14th day on the nondominant hand. The same was repeated on dominant hand on first and seventh days; 31 completed the protocol.

Results

Pain threshold and tolerance in the nondominant hand increased from day 1 to day 7 (p < 0.001) and were positively correlated on day 1 ( ρ =0.45, p = 0.011) and day 7 ( ρ =0.38, p = 0.036). Diastolic blood pressure response was found to increase by day 7 (p < 0.0024) and positively correlated with tolerance. On the dominant hand, the threshold reduced from day 1 to day 7, while tolerance increased. Both threshold and tolerance remained lower than that of nondominant hand. Day 14 values of threshold and tolerance were in between day 1 and day 7 values but not significantly different from both.

Conclusion

Habituation in pain threshold and tolerance was observed on repeated exposure to cold pain, which was not significantly retained till the 14th day. The same was not observed with subjective feeling of pain perception. The increased diastolic blood pressure response is suggestive of peripheral vasoconstriction. Increased tolerance in the dominant hand by day 7 demonstrates a systemic effect in habituation.

Effects of regular cannabis and nicotine use on acute stress responses: chronic nicotine, but not cannabis use, is associated with blunted adrenocortical and cardiovascular responses to stress

RATIONALE

Cannabis is one of the most prevalent substances used by tobacco smokers and, in light of the growing list of states and territories legalizing cannabis, it is expected that co-use of cannabis and nicotine will escalate significantly and will lead to continuing challenges with tobacco use.

OBJECTIVES

This study was conducted to examine the interactive effects of chronic cannabis and nicotine use on adrenocortical, cardiovascular, and psychological responses to stress and to explore sex differences in these effects.

METHODS

Participants (N = 231) included cannabis-only users, nicotine-only users, co-users of both substances, and a non/light-user comparison group. After attending a medical screening session, participants completed a laboratory stress session during which they completed measures of subjective states, cardiovascular responses, and salivary cortisol during baseline (rest) and after exposure to acute stress challenges.

RESULTS

Nicotine use, but not cannabis use, was associated with blunted cortisol and cardiovascular responses to stress across both men and women. Men exhibited larger cortisol responses to stress than women. Co-users had significantly larger stress-related increases in cannabis craving than cannabis-only users. Cannabis users reported smaller increases in anxiety during stress than cannabis non/light-users, and both male nicotine-only users and male cannabis-only users experienced significantly smaller increases in stress than their non/light-user control counterparts.

CONCLUSIONS

This study replicates and extends earlier research on the impacts of sex and nicotine use on stress responses, and it provides novel findings suggesting that when co-used with nicotine, cannabis use may not confer additional alterations to physiological nor subjective responses to stress. Co-use, however, was associated with enhanced stress-related craving for cannabis.

Hypertensive Hypoalgesia in a Complex Chronic Disease Population

Hypertension-related hypoalgesia, defined as lower pain sensitivity in individuals with high blood pressure, has yet to be examined in a large-scale study of complex care residents. Here, the Continuing Care Reporting System database, which contains health information on residents of Canadian complex chronic care facilities, was used for assessment. Hypertension was reported among 77,323 residents (55.5%, total N = 139,920). Propensity score matching, with a 1:1 ratio, was used to identify a control record without hypertension for each case. Multinomial logistic regression was used to quantify the effects of hypertension and sex on four-level ordinal pain variables, controlling for potential confounders. The matched dataset included n = 40,799 cases with hypertension and n = 40,799 without hypertension, with 57% female. Residents with hypertension had significantly lower odds of reporting pain (yes/no) (OR = 0.85, 95% CI 0.81–0.90, p < 0.001), including on measures of severe pain (OR = 0.69, 95% CI 0.63–0.76, p < 0.001). A significant interaction between hypertension and sex (OR = 1.17, 95% CI 1.03–1.32, p = 0.014) indicated that a significantly greater proportion of females without hypertension reported severe pain (8.71%). The results confirm the relationship between hypertension and reduced pain sensitivity on a population level.

Blood pressure-related hypoalgesia: a systematic review and meta-analysis

OBJECTIVE

Spontaneous or experimentally induced high blood pressure (BP) is associated with reduced pain perception, known as BP-related hypoalgesia. Despite its clinical implications, such as the interference with early detection of myocardial infarction in 'at risk' groups, the size of the association between high BP and pain has not yet been quantified. Moreover, the distinct association between high BP and physiological or psychological components of pain has not yet been considered so far. The aim of this study was to overcome this gap by performing separate meta-analyses on nociceptive response versus quantifiable perceptual measures of pain in relation to high BP.

METHODS

PubMed and Web of Knowledge databases were searched for English language studies conducted in humans. Fifty-nine studies were eligible for the analyses. Pooled effect sizes (Hedges' g) were compared. Random effect models were used. Results show that higher BP is significantly associated with lower nociceptive response (g = 0.38; k = 6) and reduced pain perception, assessed by quantifiable measures (g = 0.48; k = 59).

RESULTS

The association between BP and pain perception, derived from highly heterogeneous studies, was characterized by significant publication bias. BP assessment, pain assessment, site of pain stimulation, percentage of female participants in the sample, and control for potential confounders were significant moderators.

CONCLUSION

Current meta-analytic results confirm the presence of BP-related hypoalgesia and point towards the need for a better understanding of its underlying mechanisms.

Neurobiological mechanisms of early life adversity, blunted stress reactivity and risk for addiction

Blunted stress reactivity resulting from early exposure to stress during childhood and adolescence may increase vulnerability to addiction. Early life adversity (ELA) affects brain structure and function and results in blunted stress axis reactivity. In this review, we focus on the underlying neurobiological mechanisms associated with a blunted response to stress, ELA, and risk for addictive disorders. ELA and blunted reactivity are accompanied by unstable mood regulation, impulsive behaviors, and reduced cognitive function. Neuroimaging studies reveal cortical and subcortical changes in persons exposed to ELA and those who have a genetic disposition for addiction. We propose a model in which blunted stress reactivity may be a marker of risk for addiction through an altered motivational and behavioral reactivity to stress that contribute to disinhibited behavioral reactivity and impulsivity leading in turn to increased vulnerability for substance use. Evidence supporting this hypothesis in the context of substance use initiation, maintenance, and risk for relapse is presented. The effects of ELA on persons at risk for addiction may lead to early experimentation with drugs of abuse. Early adoption of drug intake may alter neuroregulation in such vulnerable persons leading to a permanent dysregulation of motivational responses consistent with dependence. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Contribution of Baroreceptor Function to Pain Perception and Perioperative Outcomes

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain homeostasis by coordinating physiologic responses to external and internal stimuli. While it is recognized that carotid and cardiopulmonary baroreceptor reflexes modulate autonomic output to mitigate excessive fluctuations in arterial blood pressure and to maintain intravascular volume, increasing evidence suggests that baroreflex pathways also project to key regions of the central nervous system that regulate somatosensory, somatomotor, and central nervous system arousal. In addition to maintaining autonomic homeostasis, baroreceptor activity modulates the perception of pain, as well as neuroimmune, neuroendocrine, and cognitive responses to physical and psychologic stressors. This review summarizes the role that baroreceptor pathways play in modulating acute and chronic pain perception. The contribution of baroreceptor function to postoperative outcomes is also presented. Finally, methods that enhance baroreceptor function, which hold promise in improving postoperative and pain management outcomes, are presented.

Exploring the Association of Hypertension With Risk for Depression: Evidence for Tamed Neurobehavioral Arousal Versus Central Emotional Dysregulation

Depression is an established predictor of adverse cardiovascular disease outcomes. Less is known about cardiovascular risk factors as predictors of depression. In this issue of Psychosomatic Medicine (2018;80:508-514), Patel et al. report data indicating that pre-existing hypertension may be inversely associated with the atypical but not typical form of depression. We highlight here the strengths and limitations of the article and discuss the findings in light of research linking blood pressure and emotion regulation. In general, evidence suggests that higher blood pressure is associated with reduced expression of negative emotions and pain. Two prominent models of interaction have been proposed and supported by epidemiological and experimental research: one assumes that elevations in blood pressure lead to reduced arousal and pain sensitivity through baroreceptor activation and possibly additional afferent mechanisms. Operant conditioning may then result in (chronic) hypertension. The other one posits that impaired emotion processing as indicated by dampened emotion recognition may lead to disinhibition of hypothalamic centers and thereby result in sustained increases in blood pressure. These models are described in context of the current literature and open research questions are formulated.

Hypertension and Postoperative Pain: A Prospective Observational Study

Objectives

The relationship between pain and hypertension is of great pathophysiological and clinical interest in the pain field, but the mechanism is poorly understood. This study used the postoperative patient-controlled analgesia (PCA) dose and the visual analysis scale (VAS) score to assess the relationship between pain and hypertension.

Methods

In this prospective study in a single-center hospital, 200 participants were enrolled and divided into three groups: normotensive group, hypertension without treatment group, and hypertension with treatment group. The participants scheduled for elective inhalational general anesthesia were interviewed at hospital admission.

Results

A significant difference was observed in analgesic dosage on postoperative days 1, 2, and 3 between the female normotensive group and female hypertension with treatment group (independent-samples, one-way analysis of covariance, age, and weight as covariates:P=0.021, 0.014, 0.032). No significant differences in the VAS scores and PCA dosages were observed between the male normotensive group and any one of the male hypertensive groups.

Conclusion

We agree that hypertensive hypoanalgesia exists in some experimental settings. The mechanism linking postoperative pain and hypertension is far more complex than we initially believed. Therefore, more studies are required to investigate the roles that antihypertensive drugs, sex, and psychological stress play. Antihypertensive drugs may play a crucial role in mediating the relationship between pain and hypertension. Psychosocial factors were discussed but were not examined.

Stress and Addiction: When a Robust Stress Response Indicates Resiliency

OBJECTIVE

Stress reactivity research has traditionally focused on the idea that exaggerated responses to stress may have adverse effects on health. Accumulating evidence suggests that attenuated responses to stress and delayed recovery may also be problematic.

METHODS

This review focuses on the role of the stress response of the hypothalamic-pituitary-adrenocortical axis, the endogenous opioid system, and the cardiovascular system in hypertension, pain perception, and addictive behaviors. Results from multiple methods of assessment and stress paradigms conducted in our laboratory over the past two decades are integrated with research from other investigators and with existing theories.

RESULTS

Research indicates that exaggerated biological and physiological responses to stress and attenuated pain perception are associated with hypertension and risk for cardiovascular diseases. This research complements work linking reduced stress responses with enhanced pain sensitivity and discomfort. Multiple studies have also demonstrated that an attenuated stress response is linked to exacerbation of withdrawal symptoms and relapse in nicotine addiction. Evidence indicates important moderators (i.e., sex, personality traits, and early life adversity) and hypothalamic-pituitary-adrenocortical- and endogenous opioid system-related mechanisms in the altered response to stress. I integrate these findings in a conceptual model emphasizing that robust stress responses in the context of addiction and relapse should be considered as a marker of resiliency.

CONCLUSIONS

A blunted stress response may indicate long-term physiological dysregulation that could usher harmful consequences for cardiovascular disease, pain perception, and addictive disorders. The impact of dysregulation is influenced by multiple individual and situational factors that should be considered in evaluating the clinical significance of stress response dysregulation.

Relations between the characteristics and psychological comorbidities of chronic pruritus differ between men and women: women are more anxious than men

BACKGROUND

Although sex and gender are becoming more important in diagnostics and therapy, there is still little knowledge about sex-specific differences in chronic pruritus (CP).

OBJECTIVES

To compare, taking into consideration the characteristics of pruritus, sex-specific differences in psychological symptoms in patients with CP.

METHODS

Sociodemographic data, data on the clinical characteristics of the skin and CP were documented over a 1-year period in all patients attending the Competence Center Chronic Pruritus of the University Hospital Münster for the first time. All patients completed the Hospital Anxiety and Depression Scale. Student's t-tests for independent study groups and linear regression analyses were applied.

RESULTS

A total of 619 patients (278 men, 341 women) were included in the analysis. Women were more anxious than men, but were not more depressed. A linear regression analysis indicated that depression and anxiety scores in women were related to the average intensity of pruritus during the previous 4 weeks and to a more generalized pruritus at the beginning of CP; older age in women also correlated with the scores on the depression subscale. Interestingly, the associations were different in men: scores on the depression scale were associated with the diagnosis of CP pruritus with multiple scratch lesions.

CONCLUSIONS

There are sex-specific differences in the relationship between the psychological symptoms and clinical characteristics of CP; higher anxiety scores were achieved by women. Whether psychological symptoms can be reversed when CP and scratch lesions improve is an issue that needs further exploration.

Nicotine withdrawal and stress-induced changes in pain sensitivity: a cross-sectional investigation between abstinent smokers and nonsmokers

Chronic smoking has been linked with alterations in endogenous pain regulation. These alterations may be pronounced when individuals quit smoking because nicotine withdrawal produces a variety of psychological and physiological symptoms. Smokers interested in quitting (n = 98) and nonsmokers (n = 37) completed a laboratory session including cold pressor test (CPT) and heat thermal pain. Smokers set a quit date and completed the session after 48 h of abstinence. Participants completed the pain assessments once after rest and once after stress. Cardiovascular and nicotine withdrawal measures were collected. Smokers showed blunted cardiovascular responses to stress relative to nonsmokers. Only nonsmokers had greater pain tolerance to CPT after stress than after rest. Lower systolic blood pressure was related to lower pain tolerance. These findings suggest that smoking withdrawal is associated with blunted stress response and increased pain sensitivity.

Vocal indices of stress: a review

OBJECTIVE

Identification of stress patterns in the voice has multiple potential applications. The objective was to review literature pertaining to the effects of various forms of stress upon the healthy voice.

STUDY DESIGN

Literature review, discussion of results, and direction for further study.

METHODS

This review article offers a model of stress and a review of the historical and recent research into the effects of stress on the voice. Electronic databases were searched using the key words. No studies were excluded on the basis of design; however, an attempt was made to include in the discussion studies which primarily address physiological and acoustic vocal parameters. The results of greater than 50 studies examining the effect of stressors ranging from lie and guilt to high altitude and space flight upon the voice were included in the review.

RESULTS

Increase in fundamental frequency is the most commonly reported effect of stress in well-controlled trials. The trend, however, is not universal. A reduction in noise as reflected by the diminished vocal jitter is reported, but less frequently.

CONCLUSIONS

Stress types, gender, and individual differences in baseline autonomic tone may explain the primarily equivocal findings of effects of stressor exposure or perceived stress on voice; and as such, the article concludes with a discussion of directions for future study.

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.

Hypoalgesia related to elevated resting blood pressure is absent in adolescents and young adults with a history of functional abdominal pain

Elevated resting blood pressure (BP) is hypoalgesic in healthy individuals, but this effect is absent in adults with chronic somatic pain. This study tested whether BP-related hypoalgesia is similarly altered in individuals with a history of chronic visceral pain in childhood. Resting BP was assessed in 94 adolescents and young adults with a known history of childhood functional abdominal pain (FAP) and 55 comparable healthy controls. Responses to an acute heat pain stimulus were then evaluated following exposure to two laboratory stressors. A significant participant type x systolic BP (SBP) interaction (p<.005) revealed that elevated resting SBP was associated with significantly higher heat pain threshold (p<.001) in healthy controls, but was unrelated to pain threshold in the FAP group. A similar pattern was observed for heat pain tolerance, with elevated SBP linked to significantly higher pain tolerance (p<.05) in healthy controls, but unrelated to tolerance in the FAP group. Dysfunction in BP-related hypoalgesia associated with FAP was evident regardless of whether childhood FAP had resolved or still persisted at the time of laboratory testing. Subgroup analyses indicated that BP-related hypoalgesia (in healthy controls) and FAP-linked absence of this hypoalgesia was observed only among females. Result suggest that childhood visceral chronic pain may be associated with relatively long-lasting dysfunction in overlapping systems modulating pain and BP that persists even after FAP resolves. Potential implications for later hypertension risk are discussed.

Hypoalgesia associated with elevated resting blood pressure: evidence for endogenous opioid involvement

This study used a placebo-controlled, between-subjects opioid blockade design to evaluate endogenous opioid involvement in the hypoalgesia associated with elevated resting blood pressure (BP) in 163 healthy individuals. Participants were randomly assigned to Drug condition (placebo, naltrexone) and Task Order (computerized maze task with harassment followed by an ischemic pain task or vice versa). Resting BP was assessed, followed by drug administration, and then the pain and maze tasks. A significant Drug x Systolic BP (SBP) interaction was observed on McGill Pain Questionnaire-Affective pain ratings (P < .01), indicating that BP-related hypoalgesia observed under placebo was absent under opioid blockade. A significant Gender x Drug x SBP x Task Order interaction was observed for VAS pain intensity (P < .02). Examination of simple effects comprising this interaction suggested that BP-related hypoalgesia occurred only in male participants who experienced the pain task in the absence of emotional arousal, and indicated that this hypoalgesia occurred under placebo but not under opioid-blockade. Results suggest that under some circumstance, BP-related hypoalgesia may have an endogenous opioid-mediated component in healthy individuals, particularly men.

Blunted opiate modulation of hypothalamic-pituitary-adrenocortical activity in men and women who smoke

OBJECTIVE

To examine the extent to which nicotine dependence alters endogenous opioid regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis functions. Endogenous opiates play an important role in regulating mood, pain, and drug reward. They also regulate the HPA functions. Previous work has demonstrated an abnormal HPA response to psychological stress among dependent smokers.

METHODS

Smokers and nonsmokers (total n = 48 participants) completed two sessions during which a placebo or 50 mg of naltrexone was administered, using a double-blind design. Blood and saliva samples, cardiovascular and mood measures were obtained during a resting absorption period, after exposure to two noxious stimuli, and during an extended recovery period. Thermal pain threshold and tolerance were assessed in both sessions. Participants also rated pain during a 90-second cold pressor test.

RESULTS

Opioid blockade increased adrenocorticotropin, plasma cortisol, and salivary cortisol levels; these increases were enhanced by exposure to the noxious stimuli. These responses were blunted in smokers relative to nonsmokers. Smokers tended to report less pain than nonsmokers, and women reported more pain during both pain procedures, although sex differences in pain were significant only among nonsmokers.

CONCLUSIONS

We conclude that nicotine dependence is associated with attenuated opioid modulation of the HPA. This dysregulation may play a role in the previously observed blunted responses to stress among dependent smokers.

Gender-specific adaptations of upper trapezius muscle activity to acute nociceptive stimulation

This study examined gender differences in the effect of experimental muscle pain on changes in the relative activation of regions of the upper trapezius muscle during a sustained contraction. Surface electromyographic (EMG) signals were recorded from multiple locations over the upper trapezius muscle with a 10 x 5 grid of electrodes from nine women and nine men during 90 degrees shoulder abduction sustained for 60s. Measurements were performed before and after the injection of 0.4 ml hypertonic (painful) and isotonic (control) saline into the cranial region of the upper trapezius muscle. The EMG root mean square (RMS) was computed for each location of the grid to form a map of the EMG amplitude distribution. The peak pain intensity following the injection of hypertonic saline was greater for women (numerical rating scale 0-10: women 6.0+/-2.1, men 4.2+/-0.9; P<0.01). For both genders, upper trapezius RMS averaged across the grid decreased following the injection of hypertonic saline (P<0.0001). Moreover, there was a relatively larger pain-induced decrease in RMS in the cranial region compared to the caudal region of the muscle for both genders. During the non-painful sustained contractions, the EMG RMS progressively increased more in the cranial than the caudal region, for both men and women, due to fatigue. This mechanism was maintained in men but not in women during the painful condition. The results demonstrate that muscle pain alters the normal adaptation of upper trapezius muscle activity to fatigue in women but not in men.

Studying sex and gender differences in pain and analgesia: a consensus report

In September 2006, members of the Sex, Gender and Pain Special Interest Group of the International Association for the Study of Pain met to discuss the following: (1) what is known about sex and gender differences in pain and analgesia; (2) what are the "best practice" guidelines for pain research with respect to sex and gender; and (3) what are the crucial questions to address in the near future? The resulting consensus presented herein includes input from basic science, clinical and psychosocial pain researchers, as well as from recognized experts in sexual differentiation and reproductive endocrinology. We intend this document to serve as a utilitarian and thought-provoking guide for future research on sex and gender differences in pain and analgesia, both for those currently working in this field as well as those still wondering, "Do I really need to study females?"

Reflexly evoked coactivation of cardiac vagal and sympathetic motor outflows: observations and functional implications

1. The purpose of the present review is to highlight the pattern of activity in the parasympathetic and sympathetic nerves innervating the heart during their reflex activation. 2. We describe the well-known reciprocal control of cardiac vagal and sympathetic activity during the baroreceptor reflex, but point out that this appears to be the exception rather than the rule and that many other reflexes reviewed herein (e.g. peripheral chemoreceptor, nociceptor, diving response and oculocardiac) involve simultaneous coactivation of both autonomic limbs. 3. The heart rate response during simultaneous activation of cardiac autonomic outflows is unpredictable because it does not simply reflect the summation of opposing influences. Indeed, it can result in bradycardia (peripheral chemoreceptor, diving and corneal), tachycardia (nociceptor) and, in some circumstances, can predispose to malignant arrhythmias. 4. We propose that this cardiac autonomic coactivation may allow greater cardiac output during bradycardia (increased ventricular filling time and stronger contraction) than activation of the sympathetic limb alone. This may be important when pumping blood into a constricted vascular tree, such as is the case during the peripheral chemoreceptor reflex and the diving response.

Neurokininergic mechanism within the lateral crescent nucleus of the parabrachial complex participates in the heart-rate response to nociception

We wanted to ascertain whether the lateral parabrachial nucleus was involved in mediating the heart-rate response evoked during stimulation of somatic nociceptors. Reversible inactivation of the lateral parabrachial nucleus, using a GABA(A) agonist, reduced the reflex tachycardia evoked during noxious (mechanical) stimulation of the forelimb by approximately 50%. The same effect was observed after blockade of neurokinin 1 receptors within the lateral parabrachial nucleus, indicating a possible involvement for substance P as a neurotransmitter. Immunocytochemistry revealed a strong expression of substance P-immunoreactive fibers and boutons in all lateral subnuclei, but they were particularly dense in the lateral crescent subnucleus. Histological verification showed that the most effective injection sites for attenuating the noxious-evoked tachycardia were all placed in or near to the lateral crescent nucleus of the lateral parabrachial complex. Many single units recorded from this region were activated by high-intensity brachial nerve stimulation. The brachial nerve evoked firing responses of some of these neurons was reversibly reduced after local delivery of a neurokinin 1 receptor antagonist. However, only a minority of these neurons followed a paired-pulse stimulation protocol applied to the spinal cord, suggesting a predominance of indirect projections from the spinal cord to the parabrachial nucleus. We conclude that the cardiac component of the response to somatic nociception involves indirect spinal pathways that most likely excite neurons located in the lateral crescent nucleus of the parabrachial complex via activation of neurokinin 1 receptors.

Nociception and baroreceptor stimulation in hypertension-prone men and women

We examined the effects of baroreceptor stimulation on nociceptive responding in men and women with a positive or negative parental history of hypertension. The effects of three baroreceptor conditions (stimulation, inhibition, and control) on subjective pain and nociceptive responding were evaluated during electrocutaneous sural nerve stimulation. Pain ratings were lower in men with positive parental history relative to men with negative parental history, but this difference was not found in women. Both stimulatory and inhibitory baroreceptor conditions were associated with reduced pain reports compared to the control condition. There were no significant differences in nociceptive responding as a function of parental history of hypertension. Although this study confirms a link between hypoalgesia and risk for hypertension in men, it does not support the hypothesis that this attenuated pain perception is due to enhanced baroreceptor activity.

The yin and yang of cardiac autonomic control: vago-sympathetic interactions revisited

We review the pattern of activity in the parasympathetic and sympathetic nerves innervating the heart. Unlike the conventional textbook picture of reciprocal control of cardiac vagal and sympathetic nervous activity, as seen during a baroreceptor reflex, many other reflexes involve simultaneous co-activation of both autonomic limbs. Indeed, even at 'rest', the heart receives tonic drives from both sympathetic and parasympathetic cardiac nerves. Autonomic co-activation occurs during peripheral chemoreceptor, diving, oculocardiac, somatic nociceptor reflex responses as well as being evoked from structures within the brain. It is suggested that simultaneous co-activation may lead to a more efficient cardiac function giving greater cardiac output than activation of the sympathetic limb alone; this permits both a longer time for ventricular filling and a stronger contraction of the myocardium. This may be important when pumping blood into a constricted vascular tree such as is the case during the diving response. We discuss that in some instances, high drive to the heart from both autonomic limbs may also be arrhythmogenic.

Cardiovascular reactivity and family history of hypertension: A meta-analysis

A regression-based meta-analysis examined the degree to which the effects of a family history of hypertension on cardiovascular reactivity are moderated by the magnitude of cardiovascular responses elicited in challenge/task conditions. Mean change scores for negative family history groups were regressed on mean change scores for positive family history groups. The slopes of separate regression lines obtained for systolic and diastolic blood pressure and heart rate were significantly less than 1.0 and the y-intercepts for these regression lines were significantly greater than zero. This pattern indicates that family history differences in cardiovascular reactivity to stress are greatest in situations that elicit the smallest baseline-stressor change scores in non-family-history groups.

The tridimensional personality theory and pain: harm avoidance and reward dependence traits correlate with pain perception in healthy volunteers

The aim of the present study was to examine the possible role of personality traits in determining the variability of pain perception among individuals. More specifically, it was intended to test whether or not the three personality dimensions suggested by Cloninger in 1987 - mainly harm avoidance (HA), but also reward dependence (RD), and novelty seeking (NS), can predict interpersonal differences in responsiveness to experimental pain. Seventy healthy volunteers participated in the study. Their personality traits were evaluated through Cloninger's tridimensional personality questionnaire (TPQ). Pain threshold (latency to pain onset), pain magnitude (VAS), and pain tolerance (time to withdrawal) were measured by using the cold pressor test. Bonferroni-adjusted correlations were found between HA and the pain parameters as follows: a negative correlation between HA and threshold (rho=-0.297, P(adj)=0.039); no significant correlation between HA and tolerance (rho=-0.219, P(adj)=0.207); and a trend for a positive correlation between HA and VAS (rho=0.266, P(adj)=0.081). Possible correlations between pain perception and the various possible combinations of high and low scoring for each of the three traits were also investigated. Correlations were found only for the combinations of high/low HA and high/low RD. The low HA/low RD combination demonstrated the lowest responsiveness to pain (VAS 65.2+/-21.4; tolerance 107.6+/-71.8 s), whereas the high HA/low RD combination was correlated with the highest responsiveness (VAS 83.3+/-10.8; tolerance 30.8+/-28.4 s). The results indicate that HA personality trait correlates best with pain responsiveness. As such, a high HA are likely to predict a heightened pain response. RD may modify this pattern. The possible relevant behavioral and neuro-chemical mechanisms are discussed.

Muscle pain during exercise in normotensive african american women: effect of parental hypertension history

The purpose of the present investigation was to determine the influence of parental hypertension history on leg muscle pain ratings during cycling exercise in African American women. Eighteen women (age, 19 +/- 2 years) with a positive family history (+PH) of hypertension and 16 (age, 19 +/- 1 years) with a negative family history (-PH) underwent maximal exercise and cold pressor testing. Maximal exercise was conducted on a cycle ergometer. Quadriceps muscle pain intensity ratings were obtained each minute during the maximal exercise test by using a category-ratio scale. The hand cold pressor test was used to determine cardiovascular reactivity. Repeated measures analysis of variance showed significantly lower pain ratings during exercise for the +PH group compared to the -PH group. Psychophysical power functions indicated that the +PH participants had significantly lower exponents for pain throughout exercise. Systolic blood pressure reactivity did not significantly predict pain ratings during exercise. Normotensive African American women with +PH of hypertension experienced less muscle pain during exercise compared to normotensive African American women with a -PH of hypertension. The results are consistent with data demonstrating reduced sensitivity to experimental pain stimuli in individuals at risk for developing hypertension and extend them to naturally occurring muscle pain produced by exercise.

PERSPECTIVE

African American women, a sedentary group with an elevated risk for developing hypertension and chronic pain, show the same negative relationship between +PH and pain perception as men, suggesting that central nervous system mechanisms of pain modulation are more related to family history than gender. Acute exercise provides an experimental model for manipulating naturally occurring pain in studies concerned with the association between pain and hypertension.

Sex differences in pain and hypothalamic-pituitary-adrenocortical responses to opioid blockade

OBJECTIVE

Sex differences in pain sensitivity and stress reactivity have been well documented. Little is known about the role of the endogenous opioid system in these differences. This study was conducted to compare adrenocortical, pain sensitivity, and blood pressure responses to opioid blockade using naltrexone in men and women.

METHODS

Twenty-six participants completed 2 sessions during which placebo or 50 mg of naltrexone was administered, using a double-blind, counterbalanced design. Thermal pain threshold and heat tolerance were assessed. Participants also rated pain during a 90-second cold pressor test (CPT) and completed the McGill Pain Questionnaire (MPQ) after each pain challenge. Blood and saliva samples and cardiovascular and mood measures were obtained throughout the sessions.

RESULTS

Plasma cortisol, adrenocorticotropin, beta endorphin, prolactin, and salivary cortisol levels increased similarly in men and women after naltrexone administration compared with placebo. Women reported more pain during both pain procedures and had lower thermal pain tolerance. In response to naltrexone, women exhibited reduced blood pressure responses and reduced MPQ pain ratings after CPT. No effects of naltrexone on these measures were found in men.

CONCLUSIONS

Although men and women exhibited similar hormonal responses to opioid receptor blockade, women reported less pain and showed smaller blood pressure responses during CPT. Results suggest differential effects of the endogenous opioid system on pain perception and blood pressure in men and women.

Blood pressure but not cortisol mediates stress effects on subsequent pain perception in healthy men and women

Research has demonstrated that exposure to acute stress may attenuate pain perception. Mechanisms of this effect in humans have not been determined. This study was conducted to determine the extent to which psychophysiological and adrenocortical responses to acute stress predict subsequent pain perception. One hundred and fifty-two healthy participants (80 women) were assigned to one of two conditions: rest followed by the cold pressor test (CPT; N=76) or stress followed by CPT (N=76). The stress protocol consisted of a public-speaking challenge. Participants rated their pain every 15 s during a 90-s hand CPT (0-4 degrees C), and they completed the short form of the McGill Pain Questionnaire. Salivary cortisol, mood, blood pressure (BP), and impedance cardiography measures were collected in both conditions. Women had lower BP and reported greater pain than men in both conditions (ps<0.01). Participants in the stress condition reported less pain during CPT than those in the rest condition (p=0.02). Regression analyses demonstrated that the stress effect on pain ratings was mediated by systolic BP level during stress; however, cortisol responses did not affect this relationship. Mood changes were independent predictors of pain. The study demonstrates that BP changes in response to stress mediate the stress-induced attenuation of pain perception.

[Do men and women have different perceptions of pain?]

OBJECTIVE

To evaluate possible differences between men and women's perception of a painful stimulus (venous puncture).

DESIGN

Transversal, analytic and observational study.Setting. Primary care.Participants. 709 people over 14 who attended three health centres for blood extraction. 98 cases were rejected (most because they received more than one puncture).

MAIN MEASUREMENTS

Age, sex, tobacco habit, perception of pain (through visual analogic scale from 1 to 10), complaints expressed (oral and/or by gestures) and patient's prior expectations.

RESULTS

Mean age: 47.4; 60.1% women. The intensity of pain had an average of 1.35 (SD, 1.60; mode, 0; median, 0.8). 14.7% expressed a complaint. Median of pain was 0.95 (Q3-Q1, 1.9-0.4) in men, whereas it was 0.70 (Q3-Q1, 1.725-0.3) in women (U=40.48; P=.095). No correlation was found between valuation of pain and age (R=0.055). No differences were found for smokers (median, 0.925; Q3-Q1, 1.725-0.35) or non-smokers (0.75; 1.825-0.325) (P.05). There were statistically significant valuations that varied according to the prior expectations of pain. Equally, pain was assessed as more intense by those who expressed a complaint (median, 2.1; Q3-Q1, 3.85-0.475) versus those who did not (0.625; 1.55-0.3) (P<.001).

CONCLUSIONS

We found no significant differences between men and women's perception of painful stimulus. In any case, differences were clinically irrelevant. There is wide individual variability, which suggests that the essential factors are psycho-social. We have to assess and treat properly a patient in pain, regardless of his/her gender.

The relationship between resting blood pressure and acute pain sensitivity in healthy normotensives and chronic back pain sufferers: the effects of opioid blockade

Resting blood pressure is inversely correlated with acute pain sensitivity in healthy normotensives. This study tested: (1) whether endogenous opioid activity is necessary for this adaptive relationship to occur, (2) whether this relationship is altered in chronic low back pain (LBP), and (3) whether endogenous opioid dysfunction underlies any such alterations. Fifty-one pain-free normotensives and 44 normotensive chronic LBP sufferers received opioid blockade (8 mg naloxone i.v.) or placebo blockade (saline) in randomized, counterbalanced order in separate sessions. During each session, subjects participated in a 1-min finger pressure (FP) pain task followed by an ischemic (ISC) forearm pain task. Among pain-free normotensives, elevated resting systolic (SBP) and diastolic (DBP) blood pressure were associated with significantly higher ISC pain thresholds (P values <0.05). Elevated SBP was also associated with significantly lower FP pain ratings (P<0.05). Opioid blockade had no significant effect on the BP-pain relationships detected (P values >0.10). In combined groups analyses, a significant subject typexSBP interaction (P<0.005) was found on ISC pain threshold: elevated SBP was associated with higher pain threshold in pain-free controls, but with lower pain threshold in LBP subjects. Although subject typexBP interactions on FP and ISC pain ratings were not significant, inclusion of LBP subjects in these analyses resulted in the overall relationship between BP and pain sensitivity becoming positive (P values <0.05). Opioid blockade exerted no significant main or interaction effects in these combined groups analyses (p values >0.10). Higher DBP was associated with greater clinical pain intensity among the LBP subjects (P<0.001). Overall, these results suggest: (1) endogenous opioids do not mediate the inverse relationship between resting blood pressure and acute pain sensitivity in pain-free normotensives; (2) the BP-pain sensitivity relationship is altered in chronic pain, suggesting dysfunction in pain regulatory systems, and (3) these alterations are not related to opioid dysfunction.

Somatic nociception activates NK1 receptors in the nucleus tractus solitarii to attenuate the baroreceptor cardiac reflex

There is limited information regarding the integration of visceral and somatic afferents within the nucleus of the solitary tract (NTS). We studied the interaction of nociceptive and baroreceptive inputs in this nucleus in an in situ arterially perfused, un-anaesthetized decerebrate preparation of rat. At the systemic level, the gain of the cardiac component of the baroreceptor reflex was attenuated significantly by noxious mechanical stimulation of a forepaw. This baroreceptor reflex depression was mimicked by NTS microinjection of substance P and antagonized by microinjection of either bicuculline (a GABAA receptor antagonist) or a neurokinin type 1 (NK1) receptor antagonist (CP-99994). The substance P effect was also blocked by a bilateral microinjection of bicuculline, at a dose that was without effect on basal baroreceptor reflex gain. Baroreceptive NTS neurons were defined by their excitatory response following increases in pressure within the ipsilateral carotid sinus. In 27 of 34 neurons the number of evoked spikes from baroreceptor stimulation was reduced significantly by concomitant electrical stimulation of the brachial nerve (P < 0.01). Furthermore, the attenuation of baroreceptor inputs to NTS neurons by brachial nerve stimulation was prevented by pressure-ejection of bicuculline from a multi-barrelled microelectrode (n = 8). In a separate population of 17 of 45 cells tested, brachial nerve stimulation evoked an excitatory response that was antagonized by blockade of NK1 receptors. We conclude that nociceptive afferents activate NK1 receptors, which in turn excite GABAergic interneurons impinging on cells mediating the cardiac component of the baroreceptor reflex.

Nociceptive afferents selectively modulate the cardiac component of the peripheral chemoreceptor reflex via actions within the solitary tract nucleus

Our previous findings showed that the nucleus of the solitary tract (NTS) mediated part of the tachycardia evoked during somatic noxious stimulation. Here, we investigated the interaction between somatic nociceptor- and peripheral chemoreceptor-evoked cardiac changes. We sought to determine whether this interaction occurred within the NTS, the primary site of termination of chemoreceptor afferents. In a working heart-brainstem preparation of rat, mechanical noxious activation of a forelimb evoked a tachycardia of 17.5+/-3 (mean+/-S.E.M.) b.p.m., whereas sodium cyanide (7-30 microg) stimulation of peripheral chemoreceptors produced a sub-maximal bradycardia of -140+/-15 b.p.m. During nociceptor stimulation the sodium cyanide-evoked bradycardia was attenuated to -42.6+/-12 b.p.m. but could be prevented by a multiple bilateral NTS microinjection of bicuculline (i.e. -173+/-18 b.p.m.). Furthermore, the activity of NTS neurones responding to peripheral chemoreceptor stimulation increased from 2.8+/-1.3 to 9.4+/-1.9 Hz during sodium cyanide injection (n=7; P<0.01). The latter response was attenuated reversibly to 2.9+/-0.9 Hz during simultaneous stimulation of the brachial nerve. Pressure ejection of bicuculline abolished this inhibitory action of brachial-nerve stimulation on the chemoreceptor-evoked excitatory synaptic response. We conclude that somatic noxious stimulation attenuates the chemoreceptor reflex-evoked bradycardia via a GABA(A)ergic mechanism in the NTS.

Adrenocortical and hemodynamic predictors of pain perception in men and women

Research has demonstrated that women report more pain than men, and clinical observations suggest that attenuated adrenocortical activity is associated with high pain sensitivity. The extent to which cortisol concentrations and hemodynamics contribute to gender differences in pain sensitivity has not been investigated. Thirty-four women and 31 men performed the hand cold pressor test (CPT). Participants rated their pain every 15 s during a 90-s CPT and a 90-s post-CPT recovery period and reported pain using the McGill Pain Questionnaire (MPQ). Salivary cortisol samples and cardiovascular measures were collected prior to, during, and after the CPT. Women reported greater pain than men during and after the CPT and on the MPQ (Ps<0.01). CPT disrupted the expected diurnal decline in cortisol, as shown by a significant increase in cortisol concentration post-CPT (P<0.01) in men and women. Regression analyses revealed that pre-CPT cortisol concentrations predicted lower pain reports during and after CPT in men only (P<0.01). Systolic blood pressure (BP) and stroke volume correlated negatively with pain reports only in women (Ps<0.05). Controlling for potential confounding variables did not alter these relationships. The negative association between pre-CPT cortisol and pain perception in men and the association between BP and pain in women demonstrate different physiological predictors of pain perception in men and women.

Role of the solitary tract nucleus in mediating nociceptive evoked cardiorespiratory responses

We compared the cardiorespiratory reflex responses evoked by noxious stimulation of the forelimb and cornea. Due to the depressant effects of anaesthesia on visceral reflexes we compared data from an unanaesthetised decerebrate rat model--the working heart-brainstem preparation (WHBP), with the anaesthetised rat. In both experimental models stimulation of the forelimb (mechanical pinch) evoked a tachycardia (WHBP: 19 +/- 2 bpm) and a decrease in respiratory cycle length (WHBP: from 4.1 +/- 0.2 to 2.3 +/- 0.1 s). The magnitude of response in anaesthetised animals depended on anaesthetic depth. Mechanical stimulation of the cornea evoked a bradycardia (-49.2 +/- 4.8 bpm) and an increase in respiratory cycle length from 4 +/- 0.36 to 5.88 +/- 0.2 s which was only present in the WHBP. In the WHBP activation of forelimb and corneal nociceptors both elicited significant pressor effects; in anaesthetised rats there were inconsistent changes in arterial pressure. To determine a role for the nucleus of the solitary tract (NTS) in mediating nociceptive evoked responses in the WHBP, synaptic transmission was blocked reversibly following bilateral microinjections of cobalt chloride. The heart rate responses evoked from either forelimb or corneal nociceptors were attenuated by approximately 50% (P < 0.05). A similar effect was observed using isoguvacine, a GABAA receptor agonist, to hyperpolarise NTS neurones. In conclusion, activation of forelimb and corneal nociceptors evoked contrasting patterns of cardiorespiratory response in the WHBP while in the anaesthetised rat the magnitude of the cardiorespiratory response to forelimb stimulation was quantitatively dependent on anaesthetic dose. In the WHBP, NTS neurones appear important for mediating the cardiac component of the reflex response following stimulation of nociceptive reflex pathways.

Blood pressure but not parental history for hypertension predicts pain perception in women

Previous work has suggested an attenuated sensitivity to painful stimulation in hypertensive men. We recently reported that, compared with persons with negative parental history, men, but not women, with a positive history for hypertension showed attenuated pain perception. This study specifically addressed factors that predict pain perception in women, including blood pressure, parental history and mood states. Fifty-four normotensive women with positive (PH+; n = 20) or negative parental history (PH-; n = 34) for hypertension and high or low casual systolic blood pressure (BP) performed the cold pressor (CP) test. Participants rated their pain every 15 s during a 90-s hand CP (0-4 degrees C) and a 90-s post-CP rest period. Detailed mood ratings were obtained immediately before the CP test. Data were evaluated using multivariate repeated measure analyses of variance and regression analyses. PH+ and PH- women did not differ in age, height, weight, education, resting BP, or heart rate. PH+ and PH- women did not differ in pain ratings during or after the CP, or pain ratings using the McGill Pain Questionnaire (MPQ), and they did not differ in their cardiovascular responses to the CP, confirming our earlier study in a separate sample. Women with high casual systolic BP reported significantly less pain, especially after the CP (P < 0.01). MPQ total scores confirmed this finding with high BP women reporting less pain than low BP women (P < 0.05). Regression analyses confirmed these effects. Controlling for potential confounding variables did not alter these relationships. These findings suggest that in women, phenotype systolic BP may be a better predictor of hypoalgesia than parental history of hypertension.