No interactive effects of naltrexone and benzodiazepines on pain during phobic fear

Stress and pain: modality-specific opioid mediation of stress-induced analgesia

Preclinical research has demonstrated that exposure to acute stress is associated with attenuated pain perception, so called stress-induced analgesia (SIA). Mechanisms of SIA in humans have not been reliably demonstrated. This study examined the role of the endogenous opioid system in the impact of combined interpersonal and mental stressors on evoked pain responses in 84 participants (34 women). Using a within-subject, double-blinded, counterbalanced design, participants were administered either oral placebo or the opioid antagonist naltrexone (50 mg) across two testing sessions. In each session, they experienced two evoked pain stimuli (cold pressor test [CPT], heat pain) after an extended rest period (rest condition) and after exposure to an acute stressor (a combination of public speaking and mental arithmetic challenge; stress condition). Results showed that both stress and opioid blockade produced significant changes in hormonal and cardiovascular measures, consistent with successful induction of acute stress. Stress was associated with attenuated pain perception (SIA) as indicated by significantly increased CPT tolerance. These effects were particularly pronounced in individuals experiencing the stress condition first. More importantly, SIA effects on CPT tolerance were abolished by opioid blockade. There were no significant SIA effects on heat pain responses. This study demonstrates that the endogenous opioid system may mediate effects of acute stress on pain perception, although this effect seems to be qualified by the type of evoked pain stimuli experienced.

Unconventional anxiety pharmacology in zebrafish: Drugs beyond traditional anxiogenic and anxiolytic spectra

Anxiety is the most prevalent brain disorder and a common cause of human disability. Animal models are critical for understanding anxiety pathogenesis and its pharmacotherapy. The zebrafish (Danio rerio) is increasingly utilized as a powerful model organism in anxiety research and anxiolytic drug screening. High similarity between human, rodent and zebrafish molecular targets implies shared signaling pathways involved in anxiety pathogenesis. However, mounting evidence shows that zebrafish behavior can be modulated by drugs beyond conventional anxiolytics or anxiogenics. Furthermore, these effects may differ from human and/or rodent responses, as such 'unconventional' drugs may affect zebrafish behavior despite having no such profiles (or exerting opposite effects) in humans or rodents. Here, we discuss the effects of several putative unconventional anxiotropic drugs (aspirin, lysergic acid diethylamide (LSD), nicotine, naloxone and naltrexone) and their potential mechanisms of action in zebrafish. Emphasizing the growing utility of zebrafish models in CNS drug discovery, such unconventional anxiety pharmacology may provide important, evolutionarily relevant insights into complex regulation of anxiety in biological systems. Albeit seemingly complicating direct translation from zebrafish into clinical phenotypes, this knowledge may instead foster the development of novel CNS drugs, eventually facilitating innovative treatment of patients based on novel 'unconventional' targets identified in fish models.

Drug-drug interactions in the treatment for alcohol use disorders: A comprehensive review

Drug interactions are one of the most common causes of side effects in polypharmacy. Alcoholics are a category of patients at high risk of pharmacological interactions, due to the presence of comorbidities, the concomitant intake of several medications and the pharmacokinetic and pharmacodynamic interferences of ethanol. However, the data available on this issue are limited. These reasons often frighten clinicians when prescribing appropriate pharmacological therapies for alcohol use disorder (AUD), where less than 15% of patients receive an appropriate treatment in the most severe forms. The data available in literature regarding the relevant drug-drug interactions of the medications currently approved in United States and in some European countries for the treatment of AUD (benzodiazepines, acamprosate, baclofen, disulfiram, nalmefene, naltrexone and sodium oxybate) are reviewed here. The class of benzodiazepines and disulfiram are involved in numerous pharmacological interactions, while they are not conspicuous for acamprosate. The other drugs are relatively safe for pharmacological interactions, excluding the opioid withdrawal syndrome caused by the combination of nalmefene or naltrexone with an opiate medication. The information obtained is designed to help clinicians in understanding and managing the pharmacological interactions in AUDs, especially in patients under multi-drug treatment, in order to reduce the risk of a negative interaction and to improve the treatment outcomes.

Separate and combined impact of acute naltrexone and alprazolam on subjective and physiological effects of oral d-amphetamine in stimulant users

RATIONALE

Opioid antagonists (e.g., naltrexone) and positive modulators of γ-aminobutyric-acidA (GABAA) receptors (e.g., alprazolam) modestly attenuate the abuse-related effects of stimulants like amphetamine. The use of higher doses to achieve greater efficacy is precluded by side effects. Combining naltrexone and alprazolam might safely maximize efficacy while avoiding the untoward effects of the constituent compounds.

OBJECTIVES

The present pilot study tested the hypothesis that acute pretreatment with the combination of naltrexone and alprazolam would not produce clinically problematic physiological effects or negative subjective effects and would reduce the positive subjective effects of d-amphetamine to a greater extent than the constituent drugs alone.

METHODS

Eight nontreatment-seeking, stimulant-using individuals completed an outpatient experiment in which oral d-amphetamine (0, 15, and 30 mg) was administered following acute pretreatment with naltrexone (0 and 50 mg) and alprazolam (0 and 0.5 mg). Subjective effects, psychomotor task performance, and physiological measures were collected.

RESULTS

Oral d-amphetamine produced prototypical physiological and stimulant-like positive subjective effects (e.g., VAS ratings of Active/Alert/Energetic, Good Effect, and High). Pretreatment with naltrexone, alprazolam, and their combination did not produce clinically problematic acute physiological effects or negative subjective effects. Naltrexone and alprazolam each significantly attenuated some of the subjective effects of d-amphetamine. The combination attenuated a greater number of subjective effects than the constituent drugs alone.

CONCLUSIONS

The present results support the continued evaluation of an opioid receptor antagonist combined with a GABAA-positive modulator using more clinically relevant experimental conditions like examining the effect of chronic dosing with these drugs on methamphetamine self-administration.

Changes in pain perception and hormones pre- and post-kumdo competition

The psychological stress of competition is a powerful stimulus affecting numerous hormones, which in turn change how pain is perceived. This study investigated whether a kumdo (kendo) team competition may be related to changes in hormones and pain. Seventeen healthy male kumdo practitioners participated in this experiment. Pain experiments were conducted by applying noxious stimuli with a thermal stimulator 10 min before a kumdo competition and 30 min post-competition. Serum testosterone, cortisol, beta-endorphin levels, pain thresholds, pain ratings at 48 °C and during blood sampling (sampling pain), anxiety, blood pressure, and heart rate were measured pre- and post-competition. Anxiety, pain threshold, testosterone/cortisol ratio, and blood pressure were significantly higher pre-competition compared to post-competition, while cortisol and pain ratings were significantly lower pre-competition than post-competition. There were significant correlations between the number of previous competitions and testosterone levels both pre-competition and post-competition. In pre-competition measurements, sampling pain increased with an increase in systolic blood pressure, heart rate, and beta-endorphins, and a decrease in age. In post-competition measurements, sampling pain increased with an increase in diastolic blood pressure and a decrease in testosterone levels. These results indicate that severe psychological pre-competition stress was associated with reduced pain ratings, perhaps in order to improve athletic performance. This also suggests that competitors may be at risk of potential injury due to changes in pain perception, and careful consideration should be taken to avoid potential injury before and during competition.

Effects of stress on pain in horses and incorporating pain scales for equine practice

The stress response represents an animal's attempt to reestablish the body's homeostasis after injury, intense physical activity, or psychological strain. Two different neuroendocrine pathways may be activated in stressful situations: the hypothalamic-pituitary-adrenocortical axis, leading to increased cortisol levels, and the sympathoadrenomedullar system, leading to increased catecholamine levels. By applying some of the evaluation methods described in this article in the appropriate clinical situations, equine veterinarians can almost certainly improve their ability to recognize and manage pain in horses.

Cold pressor pain reduces phobic fear but fear does not reduce pain

Negative emotion has a variable effect on pain perception. This variability has been explained by the motivational priming hypothesis (MPH) which predicts that emotional stimuli generating low levels of arousal will facilitate pain, while stimuli generating high levels of arousal will inhibit pain. However, a study by Sneddon et al with rainbow trout discovers a relationship not found in the human literature, that fear-related behavior decreased in the presence of a nociceptive stimulus. The current experiment examined this possibility in humans. In Experiment 1, 30 healthy, female subjects with "at least a mild aversion to spiders" participated in 3 trials: 1 in which a Brazilian salmon pink tarantula was present; a second with the right hand immersed in a cold pressor; and a third with both the tarantula and the cold pressor present. Experiment 2 added distance as an extra variable to this methodology. In both experiments it was found that spider presence had no impact upon pain perception but spider fear was reduced by the cold pressor. There was no interaction between trial and either time or distance. These findings are novel in human subjects and not well accounted for by the MPH. We suggest that an explicitly evolutionary framework should be adopted, and that spider fear was reduced to facilitate escape from the more threatening cold-pressor experience.

PERSPECTIVE

This study examined the relationship between pain and fear. Subjects with an aversion to spiders sat next to a tarantula with their right hand in iced water. Subjects reported reduced fear but no change in pain. Consequently, the authors reevaluate the Motivational Priming Hypothesis and emphasize evolutionarily determined threat values.

Influence of pharmacologically-induced experimental anxiety on nociception and antinociception in rats

Animal studies reveal that diverse environmental stimuli that generate anxiety-like behaviors also induce antinociception; conversely, clinical data show that pain perception is reduced under anxiolysis. This study was conducted to investigate the influence of pharmacologically induced-anxiety on nociception and antinociception. Experimental anxiety levels were measured using the rat burying behavior test. Diazepam (0, 0.5, 1.0 and 2.0 mg/kg, i.p.) or yohimbine (0, 0.5 and 1.0 mg/kg, i.p.) were used as anxiolytic or anxiogenic drugs, respectively. To evaluate the influence of different experimental anxiety levels on nociception, the pain-induced functional impairment in the rat (PIFIR model) was used. Nociception was induced by an intra-articular injection of 15% uric acid into the knee joint of the right hind limb. Diazepam or yohimbine were administered 15 min before uric acid and the ability of the rat to use the injured hind limb was recorded. To analyze the influence of different levels of anxiety on the antinociceptive effects produced by acetylsalicylic acid (0, 31, 100 and 310 mg/kg, p.o.); this analgesic was administered 3.5 h after uric acid. Fifteen min before diazepam (2.0 mg/kg) or yohimbine (1.0 mg/kg) were administered. We found that, in the burying behavior test, diazepam and yohimbine produced a dose-dependent decrease or augment in the cumulative time of burying, effects denoting reduced or increased experimental anxiety, respectively. Diazepam or yohimbine, administered alone, was unable to produce nociception. The results showed an influence of anxiety on nociception since a decreased (by diazepam) or increased (by yohimbine) experimental anxiety prevented nociception. Control experiments showed that acetylsalicylic acid did not modify experimental anxiety in the burying behavior test, but effectively reversed the nociception induced by uric acid (15%) in the PIFIR model. Such antinociceptive effect was unmodified by the anxiolytic or anxiogenic actions of diazepam or yohimbine. Data are discussed on the bases of clinical- and animal-studies revealing interactions between anxiety and nociception.

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.

Norepinephrine, adrenocorticotropin, cortisol and beta-endorphin in women suffering from fear of labor: responses to the cold pressor test during and after pregnancy

BACKGROUND

Women suffering from fear of labor have reduced pain tolerance during a cold pressor test (CPT) during and after pregnancy.

METHODS

We compared levels of norepinephrine, adrenocorticotropin (ACTH), cortisol and beta-endorphin before and during the CPT up to 60 min in 20 normotensive women with and 20 without fear of labor at 37.4 +/- 0.2 (mean +/- SE) gestational weeks and at 41.9 +/- 1.6 weeks after delivery.

RESULTS

Baseline levels of norepinephrine in the pregnant fear group (1.63 +/- 0.18 nmol/L) were higher (p = 0.068) than in controls (1.38 +/- 0.14 nmol/L) but after delivery they were lower in the fear group (1.75 +/- 0.31 nmol/L vs. 2.31 +/- 0.26 nmol/L, p = 0.064). ACTH, cortisol and beta-endorphin did not differ between pregnant and nonpregnant groups. The CPT caused a 28.4% smaller response in norepinephrine in the pregnant fearful women than in controls, whereas the responses of ACTH and beta-endorphin were similar between groups during and after pregnancy. The CPT caused no significant response in cortisol. Pregnant fearful women had higher diastolic blood pressure (85.6 +/- 4.5 mmHg, mean +/- SE) than the controls (74.9 +/- 3.4 mmHg, p = 0.065).

CONCLUSIONS

Women with fear of labor were characterized by changes in norepinephrine but not in ACTH, cortisol or beta-endorphin before and during the CPT, indicating a normal pituitary-adrenal axis function.

Noise stress and human pain thresholds: divergent effects in men and women

Considerable animal research suggests that exposure to noxious and nonnoxious fear-inducing stimuli can produce hypoalgesia. Although this effect is thought to generalize across species, only a few studies have examined the pain modulatory effects of nonnoxious fear-eliciting stimuli in humans. The present study examined whether exposure to a series of loud noise bursts would produce a fear-related hypoalgesia in male and female human subjects. Both subjective and physiologic measures (skin conductance level, heart rate) indicated that noise exposure resulted in fear, sympathetic arousal, and decreased pain reactivity in women (n = 20). In contrast, men (n = 20) did not experience fear or physiologic arousal, but reacted with surprise and increased pain reactivity. These findings provide additional evidence that hypoalgesia is mediated by fear and physiologic arousal. Although future studies should directly manipulate surprise, it appears that surprise without fear and physiologic arousal might enhance pain processing.

Negative affect: effects on an evaluative measure of human pain

Prior work indicates that exposure to fear-inducing shock inhibits finger-withdrawal to radiant heat in humans (hypoalgesia), whereas anxiety induced by threat of shock enhances reactivity (hyperalgesia; Pain 84 (2000) 65-75). Although finger-withdrawal latencies are thought to reflect changes in pain sensitivity, additional measures of pain are needed to determine whether pain perception is altered. The present study examined the impact of negative affect on visual analog scale (VAS) ratings of fixed duration thermal stimuli. One hundred twenty-seven male and female human subjects were randomly assigned to one of three emotion-induction conditions: (1) negative affect induced by exposure to three brief shocks; (2) negative affect elicited by the threat of shock without presentation; and (3) neutral affect, with no intervention. VAS ratings were tested before and after emotion-induction. Results suggest that both negative affect manipulations reduced pain. Manipulation checks indicated that the emotion-induction treatments induced similar levels of fear but with different arousal levels. Potential mechanisms for affect induced changes in pain are discussed.

Exacerbation of pain by anxiety is associated with activity in a hippocampal network

It is common clinical experience that anxiety about pain can exacerbate the pain sensation. Using event-related functional magnetic resonance imaging (FMRI), we compared activation responses to noxious thermal stimulation while perceived pain intensity was manipulated by changes in either physical intensity or induced anxiety. One visual signal, which reliably predicted noxious stimulation of moderate intensity, came to evoke low anxiety about the impending pain. Another visual signal was followed by the same, moderate-intensity stimulation on most of the trials, but occasionally by discriminably stronger noxious stimuli, and came to evoke higher anxiety. We found that the entorhinal cortex of the hippocampal formation responded differentially to identical noxious stimuli, dependent on whether the perceived pain intensity was enhanced by pain-relevant anxiety. During this emotional pain modulation, entorhinal responses predicted activity in closely connected, affective (perigenual cingulate), and intensity coding (mid-insula) areas. Our finding suggests that accurate preparatory information during medical and dental procedures alleviates pain by disengaging the hippocampus. It supports the proposal that during anxiety, the hippocampal formation amplifies aversive events to prime behavioral responses that are adaptive to the worst possible outcome.

The Additive Impact of Anxiety and a Placebo on Pain

OBJECTIVE

We investigated the effects of pain anxiety and a placebo/nocebo/neutral intervention on ice water-induced pain.

DESIGN

We divided 72 volunteers into high- and low-anxiety groups before randomly assigning them to experimental and control subgroups.

METHOD

Participants completed preimmersion tests of pain anxiety, pain worry, and mood. We scored first immersion pain behavior, experience, and intensity. Each subgroup then received an instruction designed to elicit a positive (placebo), negative (nocebo), or neutral response. After repeating the pain worry test, we gathered second immersion pain scores, and participants repeated the mood test, completed the treatment credibility measure, and were debriefed.

OUTCOME MEASURES

We used the Pain Anxiety Symptom Scale; self-rating Likert-type scales for pain worry, pain intensity, and pain-coping; the Multiple Affect Adjective Checklist (mood); timed measurements for pain threshold and pain tolerance; and a treatment credibility scale.

RESULTS

Pain anxiety and the placebo interventions significantly altered participants' pain scores, with best-to-worse scores reported by the low pain-anxiety/placebo, high anxiety/placebo, low anxiety/neutral, low anxiety/nocebo, high anxiety neutral, and high anxiety/nocebo groups. The high pain-anxiety group demonstrated the greatest response to the placebo/nocebo intervention in the expected directions in pain, worry, and anxious mood scores and in decreased self-confidence in managing pain (this was also negatively affected by the nocebo in each pain-anxiety group).

CONCLUSION

This study demonstrates that the interaction of the personality variable of pain anxiety with the placebo/nocebo response has an impact on pain, worry, and mood.

Reduced pain tolerance during and after pregnancy in women suffering from fear of labor

Pain tolerance in women suffering and not suffering from fear of labor during and after pregnancy were compared. Twenty women with labor fear and 20 control women were subjected to a cold pressor test (CPT) on average 1 month before delivery and 9 months later. Half the volunteers were nulliparous and half parous. Pain endurance time (PET) and intensity of pain (Visual Analogue Scale, VAS) during CPT was assessed. Patients in the fear group tolerated CPT for a significantly shorter time than did women without fear both in pregnancy (154.8+/-109.9 s vs. 282.5+/-60.1 s (mean+/-SD), P<0.001), and in the postpartum period (128.6+/-111.7 s vs. 279.6 +/-60.3 s, P=0.002). Those with labor fear experienced CPT as significantly more painful than did the controls both during pregnancy (VAS 6.68+/-1.9 vs. 3.78+/-2.0 (mean+/-SD), P<0.001) and after (VAS 7.73+/-1.5 vs. 5.92+/-3.0, P=0.04). PET and VAS values correlated during pregnancy (r=-0.62, P<0.001), but not after pregnancy (r=-0.30, not significant). Parity was not associated with either PET or VAS scores. As a rule, pain in all women during CPT was regarded to be lower during pregnancy than after pregnancy (VAS 4.87+/-2.4 vs. 6.60+/-2.6, P=0.001). Patients with fear of labor were characterized by pain intolerance also in circumstances other than labor. This fact may indicate enhanced sensitivity to pain-causing mechanisms in women who develop fear of labor.

Pain and emotion: effects of affective picture modulation

OBJECTIVE AND METHODS

Two experiments examined the impact of viewing unpleasant, pleasant, and neutral photographic slides on cold-pain perception in healthy men and women. In each experiment, participants viewed one of three slide shows (experiment 1 = fear, disgust, or neutral; experiment 2 = erotic, nurturant, or neutral) immediately before a cold-pressor task. Skin conductance and heart rate were recorded during the slide shows, whereas visual analog scale ratings of pain intensity and unpleasantness thresholds and pain tolerance were recorded during the cold-pressor task.

RESULTS

Viewing fear and disgust slides decreased pain intensity and unpleasantness thresholds, but only the fear slides decreased pain tolerance. In contrast, viewing erotic, but not nurturant, slides increased pain intensity and unpleasantness threshold ratings on the visual analog scale in men, whereas neither nurturant nor erotic slides altered pain tolerance.

CONCLUSIONS

These results are consistent with a motivational priming model that predicts that unpleasant affective states should enhance pain and that pleasant affective states should attenuate it.

The role of pain anxiety, coping, and pain self-efficacy in rheumatoid arthritis patient functioning

Anxiety about pain is increasingly recognized as one factor contributing to increased pain perception and pain behavior [McCracken, L. M., Faber S. D., & Janeck A. S. (1998) Pain-related anxiety predicts nonspecific physical complaints in persons with chronic pain. Behavior Research and Therapy, 36, 621-630; McCracken L., & Gross R. (1995). The pain anxiety symptoms scale (PASS) and the assessment of emotional responses to pain. Innovations in clinical practice: a source book, 14, 309-321]. To assess this emotional reaction to pain in chronic pain patients, McCracken, Zayfert and Gross [McCracken, L., Zayfert, C., & Gross, R. (1992). The Pain Anxiety Symptom Scale: development and validation of a scale to measure fear of pain. Pain, 50, 67-73] developed the Pain Anxiety Symptom Scale (PASS) composed of four subscales: Cognitive Anxiety, Fearful Appraisal, Escape Avoidance and Physiological Anxiety. The present study extended previous work by examining the relationship among pain anxiety dimensions, use of active and passive coping strategies and arthritis self-efficacy as predictors of functional status in 154 rheumatoid arthritis (RA) patients. Functional status was assessed using the Five-Factor Model of the Arthritis Impact Scale, 2nd ed., (AIMS2): Physical Functioning, Affective Experience, Symptoms, Social Interaction and Role Function. Hierarchical multiple regression analysis on each of the AIMS2 criterion variables showed that pain anxiety, pain and symptom self-efficacy, health status and coping strategies were able to explain between 9 and 38% of the variance in the five AIMS2 variables. The present results support the hypothesized role of pain anxiety along with previously established contributions of self-efficacy and coping strategies, in affecting physical, social, emotional and role functioning in chronic RA patients.