Nonopioid placebo analgesia is mediated by CB1 cannabinoid receptors

Increased levels of Escherichia-Shigella and Klebsiella in the gut contribute to the responsivity of placebo analgesia

Placebo analgesia is observed in both humans and animals. Given the complexity of placebo analgesia involving a variety of neurobiological, psychological, and psychosocial processes, further investigation into its underlying mechanisms is essential. Gut microbiota has been implicated in the responsivity of placebo analgesia, but its precise role remains unknown and warrants further investigations. Here, we conducted a conditioning training model with chronic inflammatory pain induced by complete Freund's adjuvant (CFA) in mice, associating parecoxib with different cues. Hierarchical clustering analysis of placebo analgesia behaviors was employed to classify mice into responders and non-responders phenotypes. Approximately 40% of CFA mice undergoing conditioning training exhibited placebo analgesia. Notably, placebo analgesia responders displayed reduced anxiety-like behaviors. 16S rRNA results revealed a distinct composition of gut microbiota composition among the control, placebo analgesia non-responders and responders groups. Notably, levels of Escherichia Shigella and Klebsiella in the gut were increased considerably in the placebo analgesia responders as compared to both control and non-responders groups. In conclusion, placebo analgesia responders demonstrated marked analgesia, reduced anxiety-like behaviors, and increased levels of Escherichia-Shigella and Klebsiella, implying a potential linkage between gut microbiota and placebo analgesia.

Visual placebo and nocebo effects

Placebo and nocebo effects modulate symptom perception through expectations and learning processes in various domains. Predominantly, their impact has been investigated on pain and physical performance. However, the influence of placebos and nocebos on visual system functionality has yet to be explored. The present study aimed to test whether placebo and nocebo effects can intervene in altering participants' performance outcomes during a novel visual accuracy task and to examine the underlying neural mechanisms through EEG. After performing a baseline session, visual accuracy was said to be enhanced or disrupted by a sham transcranial electrical stimulation over the occipital lobe. Behavioural results showed a significant increase in visual accuracy for the placebo group, from the baseline session to the test session, whereas the nocebo group showed a decrease in visual accuracy. EEG analyses on the event-related potential P300 component, conducted on both a centro-parietal electrode patch and a parieto-occipital, one displayed an increase in the amplitude of P300 for the placebo group, and a decrease in the nocebo group. These findings suggest for the first time that placebo and nocebo effects can influence visual perception and attentional processes linked to it. Overall, the present study contributes to understanding how expectations affect sensory perception beyond pain and the motor system, paving the way for investigating these phenomena in other sensory modalities such as auditory or olfactory perception. KEY POINTS: Placebo and nocebo effects have been studied predominantly in pain and motor performance fields. In a novel visual task, the impact of placebo and nocebo effects on the visual system has been evaluated, in both early components (stimuli-related) and late components (attention-related). The placebo group showed an increase in visual accuracy and EEG-evoked potential amplitudes, whereas the nocebo group showed a decrease in both. This study shows how expectations and the related placebo and nocebo effects can shape basic stimuli sensory perception in the visual domain.

Self-regulated analgesia in males but not females is mediated by endogenous opioids

Converging lines of preclinical and clinical research indicate that females, in stark contrast to males, display an increased prevalence of chronic pain. Females also demonstrate weaker analgesic efficacy in response to opioid therapies when compared with males. These sex-specific differences may be driven by dimorphic endogenous opioidergic responses. In rodent models, analgesia exhibited in males but not females was reversed by inhibiting endogenous opioidergic reception. In humans, the sex-specific endogenous system(s) supporting the direct attenuation of evoked pain has not been identified. To determine whether opioidergic blockade reverses self-regulated analgesia in males as compared to females, the present study combined two operationally analogous clinical trials (n = 98; 51 females and 47 males). In a double-blinded, counterbalanced study involving healthy (n = 39) and chronic low back pain (n = 59) populations, a high-dose naloxone (μ-, κ-, δ-opioid antagonist) vs. placebo-saline cross-over design (15 mg/kg bolus +0.1 mg/kg/h) tested the hypothesis that endogenous opioids mediate analgesia in males but not females. An 11-point visual analog scale (VAS) (0 = no pain; 10 = worst pain imaginable) evaluated pain ratings in response to noxious heat stimulation (49 °C; calf). After baseline pain testing, participants were randomized to a validated four-session mindfulness meditation or sham mindfulness meditation training intervention. Participants practiced their respective meditation during noxious heat, intravenous high-dose naloxone, and placebo saline, respectively. In males and females, meditation significantly lowered evoked pain during saline infusion. Intravenous naloxone inhibited analgesia in males, but pain relief was well preserved in females. The present findings indicate that endogenous opioids mediate self-regulated analgesia in males but not females and underscore the need to establish sex-specific pain therapeutics.

Reverse-engineering placebo analgesia

Placebo analgesia is a widely observed clinical phenomenon. Establishing a robust mouse model of placebo analgesia is needed for careful dissection of the underpinning circuit mechanisms. However, previous studies failed to observe consistent placebo effects in rodent models of chronic pain. We wondered whether strong placebo analgesia can be reverse engineered using general-anesthesia-activated neurons in the central amygdala (CeAGA) that can potently suppress pain. Indeed, in both acute and chronic pain models, pairing a context with CeAGA-mediated pain relief produced robust context-dependent analgesia, exceeding that produced by morphine in the same paradigm. CeAGA neurons receive monosynaptic inputs from temporal lobe areas that could potentially relay contextual cues directly to CeAGA neurons. However, in vivo imaging showed that CeAGA neurons were not reactivated in the conditioned context, despite mice displaying a strong analgesic phenotype. This finding suggests that the placebo-context-induced pain relief engages circuits beyond CeAGA neurons and relies on plasticity in other analgesic and/or nociceptive circuits. Our results show that conditioning with the activation of a central pain-suppressing circuit is sufficient to engineer placebo analgesia and that purposefully linking a context with an active treatment could be a means to harness the power of placebo for pain relief.

Factors associated with a placebo effect in Parkinson's disease in clinical trials: a meta-analysis

OBJECTIVES

Outcomes of clinical trials of treatment in patients with Parkinson's disease (PD) may be influenced by placebo effects. The aim of this study was to determine the factors associated with placebo effects in Parkinson's disease (PD) for guidance with design of future clinical trials.

METHODS

Factors associated with placebo effects in PD were examined in a meta-analysis using a random effects model with pooling of placebo effects on the Unified Parkinson's Disease Rating Scale part III (UPDRS III) or Movement Disorder Society sponsored revision of UPDRS III (MDS-UPDRS III). The following prespecified variables were included in the analyses: with or without drug at baseline, with or without a placebo run-in phase, with or without motor fluctuation, published year, number of study sites, placebo administration period, age, sex, disease duration, and daily levodopa dose. Publication bias was assessed by visual inspection of funnel plots and adjusted using the trim-and-fill method.

RESULTS

Thirty-eight articles with a total of 4828 subjects satisfied the inclusion criteria. There was a significant placebo effect using UPDRS III or MDS-UPDRS III (SMD = - 0.25; 95% CI - 0.35 to - 0.14; p < 0.001, I2 = 92%). Subgroup and/or multivariate meta-regression analyses revealed that placebo effects were associated with advanced PD (p = 0.04), drug exposure at baseline (p < 0.001), placebo administration period (p < 0.001), and disease duration (p < 0.01).

CONCLUSIONS

The results of this study are important as guidance in design of future clinical trials in which the influence of placebo effects is minimized.

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Expectancy Effects in Psychedelic Trials

Clinical trials of psychedelic compounds like psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltrptamine (DMT) have forced a reconsideration of how nondrug factors, such as participant expectations, are measured and controlled in mental health research. As doses of these profoundly psychoactive substances increase, so does the difficulty in concealing the treatment condition in the classic double-blind, placebo-controlled trial design. As widespread public enthusiasm for the promise of psychedelic therapy grows, so do questions regarding whether and how much trial results are biased by positive expectancy. First, we review the key concepts related to expectancy and its measurement. Then, we review expectancy effects that have been reported in both micro- and macrodose psychedelic trials from the modern era. Finally, we consider expectancy as a discrete physiological process that can be independent of, or even interact with, the drug effect. Expectancy effects can be harnessed to improve treatment outcomes and can also be actively managed in controlled studies to enhance the rigor and generalizability of future psychedelic trials.

Translating knowledge on placebo and nocebo effects into clinical practice

Introduction

Positive and negative treatment expectations are powerful modulators of health and treatment outcomes. A substantial part of treatment success is due to contextual factors modulating patient's expectations towards a treatment. Consequently, treatment expectations should be a target of therapeutic interventions themselves.

Objectives

This article highlights the neurobiological underpinnings of treatment expectations as well as strategies to modulate contextual factors to optimize treatment outcomes in daily clinical settings.

Methods

This clinical update aligns with the 2022 IASP Global Year Translating Pain Knowledge into Practice and selectively reviews the best available evidence and practice.

Results

The effects of treatment expectations, also known as placebo and nocebo effects, are observed in various clinical conditions and physiological systems. However, most of our knowledge comes from the field of pain, where expectation effects substantially contribute to overall analgesic treatment outcomes. Experimental placebo analgesia paradigms provide the best illustration of how analgesic effects can be attributed not only to a pharmacological or specific treatment, but instead are the result of the expectation towards the treatment. The impact of expectations on treatment outcome is highly variable between individuals, and the identification of factors predicting an individual's response has proven to be challenging. Further research is required to provide personalized treatment strategies for the daily clinical practice.

Conclusion

Patient's previous experiences and expectations are powerful modulators of treatment efficacy, tolerability, and adherence. By providing a comprehensive overview of recent advances in this field, this review offers valuable insights for clinicians and researchers seeking to improve patient-clinician interaction.

Creating Placebo Nonresponders in the Lab

Conditioning and expectation are known to be the main mechanisms of placebo analgesia. They may operate together, so that expectations may be enhanced by a conditioning procedure. Although most of the studies have tried to potentiate expectations through conditioning in order to generate good placebo responders, a few studies have tried to mismatch conditioning and expectations in order to investigate the subsequent administration of a placebo. In this study, we want to further investigate this mismatch. We generated incongruent associations during a conditioning procedure in which the study participants did not get what they expected. In fact, although the participants received verbal instructions of pain decrease following the administration of a placebo, we surreptitiously increased the painful electric stimulation. Two pairings of these incongruent associations (mismatch between what was expected and what was experienced) disrupted expectations of analgesia as well as the placebo effect, as assessed by measuring electric pain thresholds on the hand. The effects of mismatch conditioning on the hand extended to the contralateral arm and to a different type of pain (tourniquet), which suggests that local mismatch conditioning may affect the whole body. In all cases, expectations predicted placebo analgesia. These findings indicate that placebo nonresponders can be created in the laboratory by acting on expectations and that local effects can be generalized to other parts of the body. They also stress the importance of expectations in the therapeutic outcome, with important implications for clinical trials. PERSPECTIVE: By using mismatch conditioning, in which study participants did not get what they expected, we reduced expectations of analgesia, and this reduction abolished placebo analgesia. This effect extended to other parts of the body and other types of pain, which indicates that placebo nonresponders can be created in the laboratory.

Reverse engineering placebo analgesia

Placebo analgesia is a widely observed clinical phenomenon. Establishing a robust mouse model of placebo analgesia is needed for careful dissection of the underpinning circuit mechanisms. However, previous studies failed to observe consistent placebo effects in rodent models of chronic pain. We wondered whether strong placebo analgesia can be reverse engineered using general anesthesia-activated neurons in the central amygdala (CeA GA ) that can potently suppress pain. Indeed, in both acute and chronic pain models, pairing a context with CeA GA -mediated pain relief produced robust context-dependent analgesia, exceeding that induced by morphine in the same paradigm. We reasoned that if the analgesic effect was dependent on reactivation of CeA GA neurons by conditioned contextual cues, the analgesia would still be an active treatment, rather than a placebo effect. CeA GA neurons indeed receive monosynaptic inputs from temporal lobe areas that could potentially relay contextual cues directly to CeA GA . However, in vivo imaging showed that CeA GA neurons were not re-activated in the conditioned context, despite mice displaying a strong analgesic phenotype, supporting the notion that the cue-induced pain relief is true placebo analgesia. Our results show that conditioning with activation of a central pain-suppressing circuit is sufficient to engineer placebo analgesia, and that purposefully linking a context with an active treatment could be a means to harness the power of placebo for pain relief.

The Roles of Endogenous Opioids in Placebo and Nocebo Effects: From Pain to Performance to Prozac

Placebo and nocebo effects have been well documented for nearly two centuries. However, research has only relatively recently begun to explicate the neurobiological underpinnings of these phenomena. Similarly, research on the broader social implications of placebo/nocebo effects, especially within healthcare delivery settings, is in a nascent stage. Biological and psychosocial outcomes of placebo/nocebo effects are of equal relevance. A common pathway for such outcomes is the endogenous opioid system. This chapter describes the history of placebo/nocebo in medicine; delineates the current state of the literature related to placebo/nocebo in relation to pain modulation; summarizes research findings related to human performance in sports and exercise; discusses the implications of placebo/nocebo effects among diverse patient populations; and describes placebo/nocebo influences in research related to psychopharmacology, including the relevance of endogenous opioids to new lines of research on antidepressant pharmacotherapies.

Placebo and nocebo in the treatment of migraine: How much does real world effectiveness depend on contextual effects?

PURPOSE

Treatments in medicine impact individuals beyond their intended effects, due to phenomena such as the placebo and nocebo effects. The placebo effect arises from the positive expectation of a treatment being beneficial, while the nocebo effect stems from the negative expectation of a treatment causing harm. Both in real-world practice and clinical trials, treatments can lead to outcomes unrelated to their intended mechanism of action, which we categorize as placebo and nocebo responses. These responses, combined with the inherent fluctuation in a condition's natural progression, regression to the mean, and random comorbidities, make up a significant part of the therapeutic experience. Particularly in pain management, placebo and nocebo effects play a substantial role. By addressing modifiable contextual factors such as patient expectations, lifestyle choices, and the therapeutic relationship, healthcare providers can enhance the effectiveness of migraine treatments, paving the way for a more comprehensive, individualized approach to patient care. We must also consider non-modifiable factors like personal experiences, beliefs, and information from social media and the internet.

CONCLUSION

This review offers a summary of our current understanding of the placebo and nocebo effects in migraine management.

Placebo Effect and Its Determinants in Ocular Hypotensive Therapy: Meta-analysis and Multiple Meta-regression Analysis

TOPIC

The placebo effect and its potential determinants in ocular hypotensive therapy.

CLINICAL RELEVANCE

The placebo effect has been studied and documented within a wide clinical context. It remains unclear whether placebo is effective in glaucoma treatment or, if so, which factors are determinative of effect size (ES).

METHODS

Randomized controlled trials (RCTs) of topical ocular hypotensive therapy for patients with open-angle glaucoma or ocular hypertension, conducted through June 2, 2022, were included. First, a perceived placebo effect was measured as the overall intraocular pressure (IOP) change from the baseline. It was evaluated in terms of the ES (mean difference between the baseline and the end point) and then was compared with the ES, as obtained from the untreated control participant to obtain a true placebo effect. The primary outcome was ES based on 4 weeks of treatment. Meta-analysis-based statistical pooling was performed where appropriate, and 95% confidence intervals (CIs) were used for comparison. Potential placebo effect determinants were scrutinized using a multiple meta-regression model (PROSPERO identifier, CRD42022348098).

RESULTS

A total of 40 RCTs (7829 eyes) with 33 placebo groups (2055 eyes) along with 7 untreated groups (1184 eyes) were included. Among placebo-controlled trials, placebo was determined to be effective in lowering IOP (ES, -1.30 mmHg; 95% CI, -1.75 to -0.84 mmHg). Using NMA, the ES for placebo was -2.27 mmHg (95% CI, -3.52 to -1.01 mmHg) greater than ES for untreated control participants.. According to the multiple meta-regression model, the active treatment ES was a significant factor to predict the amount of placebo effect. Placebo additionally lowered IOP by -0.45 mmHg per -1 mmHg of active treatment effect. Add-on study design and larger sample size also were associated with greater amount of placebo effect. No publication bias was evident in either a funnel plot or the Begg and Mazumdar adjusted rank correlation test results (P = 0.24).

DISCUSSION

This meta-analysis indicated that placebo is effective in lowering IOP and is superior to the effect observed for the untreated control participants. However, caution is required in interpreting the results because of the small number of untreated controlled trials and potential bias from the lack of direct comparison between the placebo and untreated arms.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Views on and experiences with medicinal cannabis among Canadian veterans who live with pain: A qualitative study

Background

During fiscal year 2021-2022, Veterans Affairs Canada (VAC) reimbursed 18,388 veterans for medicinal cannabis at a cost of $153 million. Yet, it is not known whether the reimbursement program is producing a net benefit for veterans.

Aims

This study investigated the views and experiences Canadian that veterans who live with pain have about medicinal cannabis use, including its use for the management of chronic pain, poor sleep, and emotional distress.

Methods

Twelve Canadian veterans who live with pain-eight men, four women; split across four focus groups-were recruited to participate in a semistructured discussion around their experiences with medicinal cannabis use.

Results

Using inductive thematic analysis, seven broad categories were identified: (1) cannabis use behaviors, (2) reasons for cannabis use, (3) outcomes from cannabis use, (4) facilitators of cannabis use, (5) barriers to cannabis use, (6) stigma around cannabis use, and (7) questions and concerns about cannabis use.

Conclusions

Most veterans initiated cannabis use to manage the symptoms of preexisting medical and/or mental health conditions. Despite some negative side effects, most veterans reported improvements in their overall quality of life, sleep, relationships, mood, and pain. Concern remains around the discrepancy between veterans' qualitative reports of beneficial outcomes from medicinal cannabis use and equivocal findings around the benefit-to-harm ratio in the wider literature. Currently, the VAC reimbursement program remains challenged by unclear indication for which veterans, with what condition(s), at what dose, and in what form medical cannabis is most beneficial.

The Biology of Placebo and Nocebo Effects on Experimental and Chronic Pain: State of the Art

(1) Background: In recent years, placebo and nocebo effects have been extensively documented in different medical conditions, including pain. The scientific literature has provided strong evidence of how the psychosocial context accompanying the treatment administration can influence the therapeutic outcome positively (placebo effects) or negatively (nocebo effects). (2) Methods: This state-of-the-art paper aims to provide an updated overview of placebo and nocebo effects on pain. (3) Results: The most common study designs, the psychological mechanisms, and neurobiological/genetic determinants of these phenomena are discussed, focusing on the differences between positive and negative context effects on pain in experimental settings on healthy volunteers and in clinical settings on chronic pain patients. Finally, the last section describes the implications for clinical and research practice to maximize the medical and scientific routine and correctly interpret the results of research studies on placebo and nocebo effects. (4) Conclusions: While studies on healthy participants seem consistent and provide a clear picture of how the brain reacts to the context, there are no unique results of the occurrence and magnitude of placebo and nocebo effects in chronic pain patients, mainly due to the heterogeneity of pain. This opens up the need for future studies on the topic.

Somatic and terminal CB1 receptors are differentially coupled to voltage-gated sodium channels in neocortical neurons

Endogenous cannabinoid signaling is vital for important brain functions, and the same pathways can be modified pharmacologically to treat pain, epilepsy, and posttraumatic stress disorder. Endocannabinoid-mediated changes to excitability are predominantly attributed to 2-arachidonoylglycerol (2-AG) acting presynaptically via the canonical cannabinoid receptor, CB1. Here, we identify a mechanism in the neocortex by which anandamide (AEA), another major endocannabinoid, but not 2-AG, powerfully inhibits somatically recorded voltage-gated sodium channel (VGSC) currents in the majority of neurons. This pathway involves intracellular CB1 that, when activated by anandamide, decreases the likelihood of recurrent action potential generation. WIN 55,212-2 similarly activates CB1 and inhibits VGSC currents, indicating that this pathway is also positioned to mediate the actions of exogenous cannabinoids on neuronal excitability. The coupling between CB1 and VGSCs is absent at nerve terminals, and 2-AG does not block somatic VGSC currents, indicating functional compartmentalization of the actions of two endocannabinoids.

Association between personality traits and placebo effects: a preregistered systematic review and meta-analysis

ABSTRACT

Placebo effects are ubiquitous yet highly variable between individuals and therefore strongly affect clinical trial outcomes such as pain relief. It is unclear whether dispositional psychological traits influence responsiveness to placebo. This preregistered meta-analysis and systematic review synthesized the literature investigating the association between personality traits and placebo effects. Based on 21 studies with 798 participants, we performed formal meta-analyses for 10 different personality traits, including behavioral inhibition, fun seeking, goal-drive persistence, reward responsiveness, empathic concern, empathic fantasy, perspective-taking, personal distress, optimism, and anxiety. We did not find evidence of associations between any of these traits and magnitude of placebo effects, which was supported by equivalence tests. Furthermore, we did not find evidence for moderating factors such as placebo manipulation type (conditioning or nonconditioning) or condition (pain or nonpain). These findings challenge the notion that personality influences responsiveness to placebos and contradict its utility for identifying placebo "responders" and "nonresponders."

[Placebo effects in analgesia : Influence of expectations on the efficacy and tolerability of analgesic treatment]

Expectations of patients influence the perception and neuronal processing of acute and chronic pain and modulate the effectiveness of analgesic treatment. The expectation of treatment is not only the most important determinant of placebo analgesia. Expectations of treatment also influence the efficacy and tolerability of "active" pharmacological and non-pharmacological treatment of pain. Recent insights into the psychological and neurobiological mechanisms underlying the clinically relevant effects of treatment expectations enable and call for the systematic integration and modulation of treatment expectations into analgesic treatment concepts. Such a strategy promises to optimize analgesic treatment and to prevent or reduce the burden of unwanted side effects and the misuse of analgesics, particularly of opioids. This review highlights the current concepts, recent achievements and also challenges and key open research questions.

Targeting the endocannabinoid system for the treatment of abdominal pain in irritable bowel syndrome

The management of visceral pain in patients with disorders of gut-brain interaction, notably irritable bowel syndrome, presents a considerable clinical challenge, with few available treatment options. Patients are increasingly using cannabis and cannabinoids to control abdominal pain. Cannabis acts on receptors of the endocannabinoid system, an endogenous system of lipid mediators that regulates gastrointestinal function and pain processing pathways in health and disease. The endocannabinoid system represents a logical molecular therapeutic target for the treatment of pain in irritable bowel syndrome. Here, we review the physiological and pathophysiological functions of the endocannabinoid system with a focus on the peripheral and central regulation of gastrointestinal function and visceral nociception. We address the use of cannabinoids in pain management, comparing them to other treatment modalities, including opioids and neuromodulators. Finally, we discuss emerging therapeutic candidates targeting the endocannabinoid system for the treatment of pain in irritable bowel syndrome.

Neuro-Gastro-Cannabinology: A Novel Paradigm for Regulating Mood and Digestive Health

The maintenance of homeostasis in the gastrointestinal (GI) tract is ensured by the presence of the endocannabinoid system (ECS), which regulates important physiological activities, such as motility, permeability, fluid secretion, immunity, and visceral pain sensation. Beside its direct effects on the GI system, the ECS in the central nervous system indirectly regulates GI functions, such as food intake and energy balance. Mounting evidence suggests that the ECS may play an important role in modulating central neurotransmission which affects GI functioning. It has also been found that the interaction between the ECS and microbiota affects brain and gut activity in a bidirectional manner, and a number of studies demonstrate that there is a strong relationship between GI dysfunctions and mood disorders. Thus, microbiota can regulate the tone of the ECS. Conversely, changes in intestinal ECS tone may influence microbiota composition. In this mini-review, we propose the concept of neuro-gastro-cannabinology as a novel and alternative paradigm for studying and treating GI disorders that affect mood, as well as mood disorders that imbalance GI physiology. This concept suggests the use of prebiotics or probiotics for improving the tone of the ECS, as well as the use of phytocannabinoids or endocannabinoid-like molecules, such as palmitoylethanolamide, to restore the normal intestinal microbiota. This approach may be effective in ameliorating the negative effects of GI dysfunctions on mood and/or the effects of mood disorders on digestive health.

Placebo administration for dry eye disease: a level I evidence based systematic review and meta-analysis

Background

The efficacy of various common treatment options for dry eye disease (DED) has been investigated against placebo. However, the potential beneficial effect of placebo in the management of DED is still unclear.

Aim

This meta-analysis investigated the impact of placebo administration in DED in Ocular Surface Disease Index (OSDI), Schirmer I test (SIT), tear breakup time (TBUT), corneal staining, and complications.

Method

This meta-analysis and systematic review was conducted according to the 2020 PRISMA guidelines. In March 2022, Pubmed, Web of Science, Google Scholar, and Embase were accessed. All the randomised clinical trials which investigated any active treatment against a placebo control group were considered. The following data were extracted at baseline and at last follow-up: Ocular Surface Disease Index (OSDI), tear breakup time test (TBUT), Schirmer I test (SIT), corneal staining.

Results

Data from 56 studies (12,205 patients) were retrieved. Placebo administration is not effective in improving TBUT (P = 0.3), OSDI (P = 0.2), SIT (P = 0.1) and corneal staining (P = 0.1) from baseline to last follow-up. Active treatment led to a higher TBUT and SIT compared to placebo administration (P < 0.0001). The active treatment resulted in a lower OSDI compared to placebo administration (P = 0.0005). Five studies reported data on the corneal staining. No difference was found between placebo administration and active treatment (P = 0.8).

Conclusion

Placebo administration does not impact symptoms of DED and can be successfully employed to evaluate the efficacy of active treatments.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11096-022-01439-y.

[Neurobiological and neurochemical mechanisms of placebo analgesia]

BACKGROUND

The efficacy of pain therapies can be substantially modulated by treatment expectations, which is reflected by the substantial placebo effects observed in pain (so called placebo analgesia).

QUESTION

What is currently known about the neurobiological and neurochemical mechanisms underlying placebo analgesia?

MATERIALS AND METHODS

A focused presentation of key publications in the field embedded in a structured overview of the mechanistic concepts and current theories according to recent evidence.

RESULTS

Experimental studies with functional neuroimaging showed that the effect of placebo analgesia is reflected by changes in brain activity related to pain processing and cognitive control. The important neurotransmitters involved include opioids and dopamine.

CONCLUSION

Placebo analgesia is associated with complex neurobiological and -physiological mechanisms. An advanced comprehension of these processes should be applied to optimize existing and future therapeutic approaches in pain therapy.

A systematic review and meta-analysis of placebo effect in clinical trials on chronic prostatitis/chronic pelvic pain syndrome

BACKGROUND

It is a common practice to control efficacy of pharmacological treatment with a placebo group. However, placebo itself may affect subjective and even objective results. The purpose of this study was to evaluate the placebo effect on symptoms of CP/CPPS to improve future clinical trials.

METHODS

A search at three databases (Scopus, MEDLINE, and Web of Science) was conducted to identify double-blind placebo-controlled clinical trials on the treatment of CP/CPPS published until April 2021. The primary outcome - National Institutes of Health Chronic Prostatitis Symptom Index (NIH-CPSI) score.

SECONDARY OUTCOMES

Qmax, PVR, IPSS, and prostate volume.

RESULTS

A total of 3502 studies were identified. Placebo arms of 42 articles (5512 patients, median 31 patients) were included in the systematic review. Systematic review identified positive changes in the primary endpoint, meta-analysis of 10 articles found that NIH-CPSI total score results were significantly influenced by placebo, mean difference -4.2 (95% confidence interval [CI]: -6.31, -2.09). Mean difference of NIH-CPSI pain domain was -2.31 (95% CI: -3.4, -1.21), urinary domain -1.12 (95% CI: -1.62, -0.62), quality of life domain -1.67 (95% CI: -2.38, -0.96); p < 0.001 for all. In case of the objective indicator - Qmax, there were three articles included in the meta-analysis. Qmax mean change from baseline was 0.68 (95% CI: -0.85, 2.22, p = 0.38). Systematic review showed no significant changes in pain, measured by VAS or other scores, IPSS and PVR.

CONCLUSIONS

Placebo significantly affected the subjective parameters (NIH-CPSI) and limitedly affected various other measurements of pain (visual analog scale, McGill pain questionnaire). There was no long-term effect on IPSS and objective measurements (Qmax, PVR). This study can be used in further clinical trials to develop general rules of CPPS treatment assessment.

Psycho-Neuro-Endocrine-Immunological Basis of the Placebo Effect: Potential Applications beyond Pain Therapy

The placebo effect can be defined as the improvement of symptoms in a patient after the administration of an innocuous substance in a context that induces expectations regarding its effects. During recent years, it has been discovered that the placebo response not only has neurobiological functions on analgesia, but that it is also capable of generating effects on the immune and endocrine systems. The possible integration of changes in different systems of the organism could favor the well-being of the individuals and go hand in hand with conventional treatment for multiple diseases. In this sense, classic conditioning and setting expectations stand out as psychological mechanisms implicated in the placebo effect. Recent advances in neuroimaging studies suggest a relationship between the placebo response and the opioid, cannabinoid, and monoaminergic systems. Likewise, a possible immune response conditioned by the placebo effect has been reported. There is evidence of immune suppression conditioned through the insular cortex and the amygdala, with noradrenalin as the responsible neurotransmitter. Finally, a conditioned response in the secretion of different hormones has been determined in different studies; however, the molecular mechanisms involved are not entirely known. Beyond studies about its mechanism of action, the placebo effect has proved to be useful in the clinical setting with promising results in the management of neurological, psychiatric, and immunologic disorders. However, more research is needed to better characterize its potential use. This review integrates current knowledge about the psycho-neuro-endocrine-immune basis of the placebo effect and its possible clinical applications.

Pain response to cannabidiol in induced acute nociceptive pain, allodynia, and hyperalgesia by using a model mimicking acute pain in healthy adults in a randomized trial (CANAB I)

ABSTRACT

Preclinical studies have demonstrated the analgesic potential of cannabidiol (CBD). Those suggesting an effect on pain-processing receptors have brought CBD back into focus. This study assessed the effect of CBD on acute pain, hyperalgesia, and allodynia compared with placebo. Twenty healthy volunteers were included in this randomized, placebo-controlled, double-blinded, crossover study assessing pain intensities (using numeric rating scale), secondary hyperalgesia (von Frey filament), and allodynia (dry cotton swab) in a well-established acute pain model with intradermal electrical stimulation. The authors compared the effect of 800-mg orally administered CBD on pain compared with placebo. They further examined the effect on hyperalgesia and allodynia. Cannabidiol whole blood levels were also measured. Pain ratings (mean ± SD) did not differ significantly after CBD application compared with placebo (5.2 ± 0.7 vs 5.3 ± 0.7, P-value 0.928), neither did the areas of hyperalgesia and allodynia differ significantly after CBD application compared with placebo (hyperalgesia 23.9 ± 19.2 cm2 vs 27.4 ± 17.0 cm2, P-value 0.597; allodynia 16.6 ± 13.1 cm2 vs 17.3 ± 14.1 cm2, P-value 0.884). The CBD whole blood level (median, first to third quartile) was 2.0 µg/L (1.5-5.1) 60 minutes and 5.0 µg/L (4.0-10.4) 130 minutes after CBD application. Although the oral application of 800-mg CBD failed to show a significant effect, it is important to focus future research on different dosing, routes of administration, and CBD as a part of multimodal treatment strategies before negating its effects on acute pain.

Predictive processing models and affective neuroscience

The neural bases of affective experience remain elusive. Early neuroscience models of affect searched for specific brain regions that uniquely carried out the computations that underlie dimensions of valence and arousal. However, a growing body of work has failed to identify these circuits. Research turned to multivariate analyses, but these strategies, too, have made limited progress. Predictive processing models offer exciting new directions to address this problem. Here, we use predictive processing models as a lens to critique prevailing functional neuroimaging research practices in affective neuroscience. Our review highlights how much work relies on rigid assumptions that are inconsistent with a predictive processing approach. We outline the central aspects of a predictive processing model and draw out their implications for research in affective and cognitive neuroscience. Predictive models motivate a reformulation of "reverse inference" in cognitive neuroscience, and placing a greater emphasis on external validity in experimental design.

Brainstem Mechanisms of Pain Modulation: A within-Subjects 7T fMRI Study of Placebo Analgesic and Nocebo Hyperalgesic Responses

Pain perception can be powerfully influenced by an individual's expectations and beliefs. Although the cortical circuitry responsible for pain modulation has been thoroughly investigated, the brainstem pathways involved in the modulatory phenomena of placebo analgesia and nocebo hyperalgesia remain to be directly addressed. This study used ultra-high-field 7 tesla functional MRI (fMRI) to accurately resolve differences in brainstem circuitry present during the generation of placebo analgesia and nocebo hyperalgesia in healthy human participants (N = 25, 12 male). Over 2 successive days, through blinded application of altered thermal stimuli, participants were deceptively conditioned to believe that two inert creams labeled lidocaine (placebo) and capsaicin (nocebo) were acting to modulate their pain relative to a third Vaseline (control) cream. In a subsequent test phase, fMRI image sets were collected while participants were given identical noxious stimuli to all three cream sites. Pain intensity ratings were collected and placebo and nocebo responses determined. Brainstem-specific fMRI analysis revealed altered activity in key pain modulatory nuclei, including a disparate recruitment of the periaqueductal gray (PAG)-rostral ventromedial medulla (RVM) pathway when both greater placebo and nocebo effects were observed. Additionally, we found that placebo and nocebo responses differentially activated the parabrachial nucleus but overlapped in engagement of the substantia nigra and locus coeruleus. These data reveal that placebo and nocebo effects are generated through differential engagement of the PAG-RVM pathway, which in concert with other brainstem sites likely influences the experience of pain by modulating activity at the level of the dorsal horn.SIGNIFICANCE STATEMENT Understanding endogenous pain modulatory mechanisms would support development of effective clinical treatment strategies for both acute and chronic pain. Specific brainstem nuclei have long been known to play a central role in nociceptive modulation; however, because of the small size and complex organization of the nuclei, previous neuroimaging efforts have been limited in directly identifying how these subcortical networks interact during the development of antinociceptive and pro-nociceptive effects. We used ultra-high-field fMRI to resolve brainstem structures and measure signal change during placebo analgesia and nocebo hyperalgesia. We define overlapping and disparate brainstem circuitry responsible for altering pain perception. These findings extend our understanding of the detailed organization and function of discrete brainstem nuclei involved in pain processing and modulation.

Thirty Years of Neuroscientific Investigation of Placebo and Nocebo: The Interesting, the Good, and the Bad

Over the past 30 years there has been a surge of research on the placebo effect using a neuroscientific approach. The interesting aspects of this effort are related to the identification of several biological mechanisms of both the placebo and nocebo effects, the latter of which is defined as a negative placebo effect. Some important translational implications have emerged both in the setting of clinical trials and in routine medical practice. One of the principal contributions of neuroscience has been to draw the attention of the scientific and medical communities to the important role of psychobiological factors in therapeutic outcomes, be they drug related or not. Indeed, many biological mechanisms triggered by placebos and nocebos resemble those modulated by drugs, suggesting a possible interaction between psychological factors and drug action. Unfortunately, this new knowledge regarding placebos has the potential of being dangerously exploited by pseudoscience. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Lifestyle Interventions Improving Cannabinoid Tone During COVID-19 Lockdowns May Enhance Compliance With Preventive Regulations and Decrease Psychophysical Health Complications

Studies investigating the psychosomatic effects of social isolation in animals have shown that one of the physiologic system that gets disrupted by this environment-affective change is the Endocannabinoid System. As the levels of endocannabinoids change in limbic areas and prefrontal cortex during stressful times, so is the subject more prone to fearful and negative thoughts and aggressive behavior. The interplay of social isolation on the hypothalamic-pituitary-adrenal axis and cannabinoid tone triggers a vicious cycle which further impairs the natural body's homeostatic neuroendocrine levels and provokes a series of risk factors for developing health complications. In this paper, we explore the psychosomatic impact of prolonged quarantine in healthy individuals, and propose management and coping strategies that may improve endocannabinoid tone, such as integration of probiotics, cannabidiol, meditation, and physical exercise interventions with the aim of supporting interpersonal, individual, and professional adherence with COVID-19 emergency public measures whilst minimizing their psycho-physical impact.

What can be done to control the placebo response in clinical trials? A narrative review

The desire to reduce high placebo response rates in clinical trials is a popular concept. However, few studies have rigorously examined the effectiveness of methods to control for placebo responses that are relevant to randomized controlled trials. The primary objective of this review was to evaluate the effect of experimental placebo manipulations in randomized controlled trials (RCTs). We critically reviewed studies designed to manipulate placebo responses including positive expectations regarding the effectiveness of the placebo treatment, manipulating the time spent with subjects, and training study staff and subjects to accurately report symptom severity. These efforts have generally resulted in reduced placebo response and improved discrimination between drug and placebo. Interventions that neutralize staff and subject expectations and improve the ability of subjects to accurately report symptom severity have shown the most promise. Reduction of the placebo response has the potential to accelerate the development of new therapeutics.

Mindfulness-Based Analgesia or Placebo Effect? The Development and Evaluation of a Sham Mindfulness Intervention for Acute Experimental Pain

OBJECTIVE

Meta-analyses indicate that mindfulness meditation is efficacious for chronic and acute pain, but most available studies lack active control comparisons. This raises the possibility that placebo-related processes may account, at least in part, for mindfulness effects. The objective of this study was to develop a closely matched sham mindfulness condition to establish whether placebo effects contribute to mindfulness-based interventions for pain.

METHODS

We developed and validated a closely matched sham mindfulness intervention then compared it with 6 × 20-minute sessions of focused-attention mindfulness and a no-treatment condition in 93 healthy volunteers undergoing acute experimental heat pain.

RESULTS

The sham mindfulness intervention produced equivalent credibility ratings and expectations of improvement as the mindfulness intervention but did not influence mindfulness-related processes. In contrast, mindfulness increased "observing" relative to no treatment but not sham. Mindfulness (F(1,88) = 7.06, p = .009, ηp2 = 0.07) and sham (F(1,88) = 6.47, p = .012, ηp2 = 0.07) moderately increased pain tolerance relative to no treatment, with no difference between mindfulness and sham (F(1,88) = 0.01, p = .92, ηp2 < 0.001). No differences were found for pain threshold. Similarly, neither mindfulness nor sham reduced pain intensity or unpleasantness relative to no treatment, although mindfulness reduced pain unpleasantness relative to sham (F(1,88) = 5.03, p = .027, ηp2 = 0.05).

CONCLUSIONS

These results suggest that placebo effects contribute to changes in pain tolerance after mindfulness training, with limited evidence of specific effects of mindfulness training on pain unpleasantness relative to sham, but not no treatment. To disentangle the specific analgesic effects of mindfulness from placebo-related processes, future research should prioritize developing and incorporating closely matched sham conditions.Trial Registration: Australian New Zealand Clinical Trials Registry (ACTRN12618001175268).

Naltrexone during pain conditioning: A double-blind placebo-controlled experimental trial

Naltrexone reversibly blocks the effects of opioids and has been shown to decrease placebo analgesia. However, it is not clear (1) to what extent naltrexone affects pain modulation in a nontreatment context, for example, in response to pain cues or (2) how naltrexone given prior to pain-cue learning shapes pain responses. In a double-blind procedure prior to pain-cue conditioning, 30 healthy participants were randomized to receive an oral dose of naltrexone (50 mg) or inert pill. During functional magnetic resonance imaging, high and low pain pressures were paired with two different visual cues: a high pain cue and a low pain cue (learning sequence). During a test sequence, medium levels of pressure were used for both cues and the difference in subjective pain ratings following high and low pain cues was calculated. Results showed significant conditioned pain responses across groups (P < .001); however, no significant difference between participants receiving naltrexone or inert pill (P = .193). There was a significant correlation between the difference in high and low pain ratings during the learning sequence and the effect of high and low pain cues during the test sequence (r = .575, P = .002). Functional magnetic resonance imaging analyses revealed no significant difference in brain activation between groups. Here, we demonstrate comparable learning of pain responses in participants treated with naltrexone or inert pill. The results point to the possibility that associative learning, and conditional responding to pain cues, is not dependent on endogenous opioids. Our results, using pain-cue conditioning to create reduced pain responses, contrast previous studies where opioid antagonists significantly reduced the placebo effect in treatment of pain.

Placebos and Movies: What Do They Have in Common?

Placebos are fake therapies that can induce real therapeutic effects, called placebo effects. It goes without saying that what matters for inducing a placebo effect is not so much the fake treatment itself, but rather the therapeutic ritual that is carried out, which is capable of triggering psychobiological mechanisms in the patient’s brain. Both laypersons and scientists often accept the phenomenon of the placebo effect with reluctance, as fiction-induced clinical improvements are at odds with common sense. However, it should be emphasized that placebo effects are not surprising after all if one considers that fiction-induced physiological effects occur in everyday life. Movies provide one of the best examples of how fictitious reality can induce psychological and physiological responses, such as fear, love, and tears. In the same way that a horror movie induces fear-related physiological responses, even though the viewer knows everything is fake, so the sight of a syringe may trigger the release of pain-relieving chemicals in the patient’s brain, even if the patient knows there is a fake painkiller inside. From this perspective, placebos can be better conceptualized as rituals, actions, and fictions within a more general framework that emphasizes the power of psychological factors in everyday life, including the healing context.

Bridging the Translational Divide in Pain Research: Biological, Psychological and Social Considerations

A gap exists between translating basic science research into effective pain therapies in humans. While preclinical pain research has primarily used animal models to understand biological processes, a lesser focus has been toward using animal models to fully consider other components of the pain experience, such as psychological and social influences. Herein, we provide an overview of translational studies within pain research by breaking them down into purely biological, psychological and social influences using a framework derived from the biopsychosocial model. We draw from a wide landscape of studies to illustrate that the pain experience is highly intricate, and every attempt must be made to address its multiple components and interactors to aid in fully understanding its complexity. We highlight our work where we have developed animal models to assess the cognitive and social effects on pain modulation while conducting parallel experiments in people that provide proof-of-importance for human pain modulation. In some instances, human pain research has sparked the development of novel animal models, with these animal models used to better understand the complexity of phenomena considered to be uniquely human such as placebo responses and empathy.

The placebo phenomenon and the underlying mechanisms

The clinical role of the placebo effect is a topic of increasing interest for the scientific community. Focus is shifting from the inert role of placebos in randomized controlled trials (RCTs) to potential effects in clinical applications, since the phenomenon is thought to be inherent in routine clinical practice, affecting therapy success rates. Mediation of the mind-brain-body relationship involves both psychosocial and neurobiological factors, the interaction of which comprises the placebo mechanisms. Psychosocial factors include environmentally induced expectations, reward expectations, and even conditioned responses to certain stimuli. Expectations also depend on previous experience of the patient with a similar procedure and can affect future responses. Moreover, the supportive bedside behavior of the clinician and the positive framing of information provided to the patient have proven to be of great importance, setting the foundations for reconsideration of standardized practices. Neurobiological mechanisms mediate these effects through neurotransmitter and neuromodulator pathways. The best understood mechanisms are those regulating non-opioid- and opioid-mediated analgesic responses that implicate specific brain regions of pain control and activation of endogenous opioids. Other responses concern, among others, hormonal control, motor performance, and antidepressant responses. Although mechanisms underlying placebo responses are not as yet completely elucidated, there is substantial evidence suggesting that placebo effects are indicative of healthy functioning of intact brain structures and occur through actual functional changes, and are not simply subjective symptom reports. These effects can be utilized in treatment optimization while maintaining an ethical and respectful manner toward the patient and the standardized disclosure procedures.

The Endocannabinoid System Contributes to Electroacupuncture Analgesia

The extensive involvement of the endocannabinoid system (ECS) in vital physiological and cognitive processes of the human body has inspired many investigations into the role of the ECS and drugs, and therapies that target this system and its receptors. Activation of cannabinoid receptors 1 and 2 (CB₁ and CB₂) by cannabinoid treatments, including synthetic cannabinoids, alleviates behavioral responses to inflammatory and neuropathic pain. An increasing body of scientific evidence details how electroacupuncture (EA) treatments achieve effective analgesia and reduce inflammation by modulating cannabinoid signaling, without the adverse effects resulting from synthetic cannabinoid administration. CB₁ receptors in the ventrolateral area of the periaqueductal gray are critically important for the mechanisms of the EA antinociceptive effect, while peripheral CB₂ receptors are related to the anti-inflammatory effects of EA. This review explores the evidence detailing the endocannabinoid mechanisms involved in EA antinociception.

Distinct neural networks subserve placebo analgesia and nocebo hyperalgesia

Neural networks involved in placebo analgesia and nocebo hyperalgesia processes have been widely investigated with neuroimaging methods. However, few studies have directly compared these two processes and it remains unclear whether common or distinct neural circuits are involved. To address this issue, we implemented a coordinate-based meta-analysis and compared neural representations of placebo analgesia (30 studies; 205 foci; 677 subjects) and nocebo hyperalgesia (22 studies; 301 foci; 401 subjects). Contrast analyses confirmed placebo-specific concordance in the right ventral striatum, and nocebo-specific concordance in the dorsal anterior cingulate cortex (dACC), left posterior insula and left parietal operculum during combined pain anticipation and administration stages. Importantly, no overlapping regions were found for these two processes in conjunction analyses, even when the threshold was low. Meta-analytic connectivity modeling (MACM) and resting-state functional connectivity (RSFC) analyses on key regions further confirmed the distinct brain networks underlying placebo analgesia and nocebo hyperalgesia. Together, these findings indicate that the placebo analgesia and nocebo hyperalgesia processes involve distinct neural circuits, which supports the view that the two phenomena may operate via different neuropsychological processes.

Neural effects of placebo analgesia in fibromyalgia patients and healthy individuals

ABSTRACT

Placebo analgesia is hypothesized to involve top-down engagement of prefrontal regions that access endogenous pain inhibiting opioid pathways. Fibromyalgia (FM) patients have neuroanatomical and neurochemical alterations in pathways relevant to placebo analgesia. Thus, it remains unclear whether placebo analgesic mechanisms would differ in FM patients compared to healthy controls (HCs). Here, using placebo-analgesia-inducing paradigms that included verbal suggestions and conditioning manipulations, we examined whether behavioral and neural placebo analgesic responses differed between 32 FM patients and 46 age- and sex-matched HCs. Participants underwent a manipulation scan, where noxious high and low heat were paired with the control and placebo cream, respectively, and a placebo experimental scan with equal noxious heat temperatures. Before the experimental scan, each participant received saline or naloxone, an opioid receptor antagonist. Across all participants, the placebo condition decreased pain intensity and unpleasantness ratings, decreased activity within the right insula and bilateral secondary somatosensory cortex, and modulated the neurologic pain signature. There were no differences between HCs and FM patients in pain intensity ratings or neural responses during the placebo condition. Despite the perceptual and neural effects of the placebo manipulation, prefrontal circuitry was not activated during the expectation period and the placebo analgesia was unaltered by naloxone, suggesting placebo effects were driven more by conditioning than expectation. Together, these findings suggest that placebo analgesia can occur in both HCs and chronic pain FM patients, without the involvement of opioidergic prefrontal modulatory networks.

Effects of Patients' Expectation in Dermatology: Evidence from Experimental and Clinical Placebo Studies and Implications for Dermatologic Practice and Research

Patients' expectations towards the benefit of a treatment are key determinants of placebo responses and can affect the development and course of medical conditions and the efficacy and tolerability of active medical treatment. The mechanisms mediating these placebo and nocebo effects have been best described in the field of experimental pain and placebo analgesia. However, also in dermatology experimental and clinical studies demonstrate that various skin diseases such as inflammatory dermatoses and allergic reactions can be modulated by patients' expectations. Dermatologists should consider the important modulatory role of patients' expectations on the efficacy and tolerability of specific treatments and the key role of verbal information, patients' prior treatment experiences (associative learning), and the quality and quantity of doctor-patient communication in shaping treatment expectation. As a consequence, techniques aiming at maximizing patients' expectation effects should be implemented into daily clinical routine. By contrast, in clinical studies expectation effects should be maximally controlled and harmonized to improve the "assay sensitivity" to detect new compounds. Further translational studies, also in dermatoses that have not been investigated yet, are needed to better characterize the mechanisms underlying patients' expectation and to gain further insights into potential clinical implications of these effects in dermatologic conditions. Therefore, in this review, we provide a brief overview on the concept of expectation effects on treatment outcome in general, summarize what is already known about this topic for dermatologic diseases, and finally present the relevance of this topic in clinical dermatology.

Beyond Sharing Unpleasant Affect-Evidence for Pain-Specific Opioidergic Modulation of Empathy for Pain

It is not known how specific the neural mechanisms underpinning empathy for different domains are. In the present study, we set out to test whether shared neural representations between first-hand pain and empathy for pain are pain-specific or extend to empathy for unpleasant affective touch as well. Using functional magnetic resonance imaging and psychopharmacological experiments, we investigated if placebo analgesia reduces first-hand and empathic experiences of affective touch, and compared them with the effects on pain. Placebo analgesia also affected the first-hand and empathic experience of unpleasant touch, implicating domain-general effects. However, and in contrast to pain and pain empathy, administering an opioid antagonist did not block these effects. Moreover, placebo analgesia reduced neural activity related to both modalities in the bilateral insular cortex, while it specifically modulated activity in the anterior midcingulate cortex for pain and pain empathy. These findings provide causal evidence that one of the major neurochemical systems for pain regulation is involved in pain empathy, and crucially substantiates the role of shared representations in empathy.

The subthalamic nucleus and the placebo effect in Parkinson's disease

The study of the placebo effect, or response, is related to the investigation of the psychologic component of different therapeutic rituals. The high rate of placebo responses in Parkinson's disease clinical trials provided the impetus for investigating the underlying mechanisms. Ruling out spontaneous remission and regression to the mean through the appropriate experimental designs, genuine psychologic placebo effects have been identified, in which both patients' expectations of therapeutic benefit and learning processes are involved. Specifically, placebo effects are associated with dopamine release in the striatum and changes in neuronal activity in the subthalamic nucleus, substantia nigra pars reticulata, and motor thalamus in Parkinson's disease, as assessed through positron emission tomography and single-neuron recording during deep brain stimulation, respectively. Conversely, verbal suggestions of clinical worsening or drug dose reduction induce nocebo responses in Parkinson's disease, which have been detected at both behavioral and electrophysiologic level. Important implications and applications emerge from this new knowledge. These include better clinical trial designs, whereby patients' expectations should always be assessed, as well as better drug dosage in order to reduce drug intake.

[Placebo Effect - The Benefit of "Nothingness" in Pain Therapy]

For a long time considered ineffective, placebos nowadays have an accepted role in studies as well as clinical practice. The identification of psychological as well as neurophysiological mechanisms helped to conceptualize and legitimize the placebo effect. Moreover, studies have even proven a therapeutic value. Consequently, the benefits of a thoughtfully applied placebo effect are increasingly being exploited. This article reviews the concept and current understanding of the placebo effect and depicts its use in the field of pain management.

Binding Modes and Selectivity of Cannabinoid 1 (CB1) and Cannabinoid 2 (CB2) Receptor Ligands

The cannabinoid (CB) receptors (CB₁R and CB₂R) represent a promising therapeutic target for several indications such as nociception and obesity. The ligands with nonselectivity can be traced to the high similarity in the binding sites of both cannabinoid receptors. Therefore, the need for selectivity, potency, and G-protein coupling bias has further complicated the design of desired compounds. The bias of currently studied cannabinoid agonists is seldom investigated, and agonists that do exhibit bias are typically nonselective. However, certain long-chain endocannabinoids represent a class of selective and potent CB₁R agonists. The binding mode for this class of compounds has remained elusive, limiting the implementation of its binding features to currently studied agonists. Hence, in the present study, the binding poses for these long-chain cannabinoids, along with other interesting ligands, with the receptors have been determined, by using a combination of molecular docking and molecular dynamics (MD) simulations along with molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) binding free energy calculations. The binding poses for the long-chain cannabinoids implicate that a site surrounded by the transmembrane (TM)2, TM7, and extracellular loop (ECL)2 is vital for providing the long-chain ligands with the selectivity for CB₁R, especially I267 of CB₁R (corresponding to L182 of CB₂R). Based on the obtained binding modes, the calculated relative binding free energies and selectivity are all in good agreement with the corresponding experimental data, suggesting that the determined binding poses are reasonable. The computational strategy used in this study may also prove fruitful in applications with other GPCRs or membrane-bound proteins.

Why we need more research into the placebo response in psychiatry

Placebos are not inert, but exert measurable biological effects. The placebo response in psychiatric illness is important and clinically relevant, but remains poorly understood. In this paper, we review current knowledge about the placebo response in psychiatric medicine and identify research directions for the future. We argue that more research is needed into the placebo response in psychiatric medicine for three broad reasons. First, awareness of factors that cause placebo response, for whom, and when, within clinical trials will allow us to better evidence efficacy of new treatments. Second, by understanding how placebo mechanisms operate in the clinic, we can take advantage of these to optimise the effects of current treatments. Finally, exploring the biological mechanisms of placebo effects might reveal tractable targets for novel treatment development.

Molecular classification of the placebo effect in nausea

In this proof-of-concept study, we tested whether placebo effects can be monitored and predicted by plasma proteins. In a randomized controlled design, 90 participants were exposed to a nauseating stimulus on two separate days and were randomly allocated to placebo treatment or no treatment on the second day. Significant placebo effects on nausea, motion sickness, and (in females) gastric activity could be verified. Using label-free tandem mass spectrometry, 74 differentially regulated proteins were identified as correlates of the placebo effect. Gene ontology (GO) enrichment analyses identified acute-phase proteins and microinflammatory proteins to be involved, and the identified GO signatures predicted day-adjusted scores of nausea indices in the placebo group. We also performed GO enrichment analyses of specific plasma proteins predictable by the experimental factors or their interactions and identified 'grooming behavior' as a prominent hit. Finally, Receiver Operator Characteristics (ROC) allowed to identify plasma proteins differentiating placebo responders from non-responders, comprising immunoglobulins and proteins involved in oxidation reduction processes and complement activation. Plasma proteomics is a promising tool to identify molecular correlates and predictors of the placebo effect in humans.

Der Placeboeffekt in der Schmerztherapie – für den klinischen Alltag nutzbar? Ja, unbedingt!

Als Placeboeffekte bezeichnet man positive physiologische oder psychologische Veränderungen, die nach einer Einnahme von Medikamenten ohne spezifischen Wirkstoff oder Scheineingriffen auftreten und durch Erwartungs- und Konditionierungsprozesse induziert werden. Die mit Placeboeffekten einhergehenden neurobiologischen und peripher-physiologischen Vorgänge können auch bei der Vergabe von wirkstoffhaltigen Medikamenten eine wichtige Rolle spielen und sind somit nicht zwingend an die Gabe eines Scheinmedikamentes gebunden. Die Darreichung von „traditionellen“ Placebos ist im klinischen Alltag aus juristischen und ethischen Gründen höchst problematisch. Dieser Beitrag zeigt neben neuen Erkenntnissen zu offenen Placebo-Anwendungen (Open-Label Placebos) Wege auf, wie die zugrundeliegenden Mechanismen von Placeboantworten dennoch gezielt im schmerztherapeutischen Alltag genutzt werden können, um die Wirksamkeit, Verträglichkeit und Compliance bestehender pharmakologischer und anderer Therapien zum Wohle des Patienten zu optimieren.