Placebo analgesia affects the behavioral despair tests and hormonal secretions in mice

Behaviorally conditioned effects of psychoactive drugs in experimental animals: What we have learned from nearly a century of research and what remains to be learned

Continuous treatment with drugs is a crucial requirement for managing various clinical conditions, including chronic pain and neuropsychiatric disorders such as depression or schizophrenia. Associative learning processes, i.e. Pavlovian conditioning, can play an important role for the effects of drugs and could open new avenues for optimizing patient treatment. In this narrative literature review, we summarize available data in experimental animals regarding the behaviorally conditioned effects of psychostimulants such as d-amphetamine and cocaine, the dopamine receptor agonist apomorphine, the dopamine receptor antagonist haloperidol, morphine and antidepressant drugs. In each section, the drug under discussion is briefly introduced, followed by a detailed examination of conditioning features, including doses and dosing regimens, characteristics of the conditioning process such as test environments or specific conditioned stimuli, testing and conditioned response characteristics, possible extinction or reconditioning or reversal training, neural mechanisms, and finally, the potential clinical relevance of the research area related to the drug. We focus on key outcomes, delve into methodical issues, identify gaps in current knowledge, and suggest future research directions.

Short-active gestational photoperiod reduces effortful choice behavior in mice, partial normalization by d-amphetamine

RATIONALE

Seasonal birth patterns consistently implicate winter gestation as a risk factor for several psychiatric conditions. We recently demonstrated that short-active (SA; 19:5 light:dark)-i.e., "winter-like"-photoperiod exposure across gestation and early life (E0-P28) induces psychiatrically relevant behavioral abnormalities in adult mice, including reduced immobility in the forced swim test (FST) and effortful amotivation. It is unknown, however, whether these effects were driven primarily by prenatal or postnatal mechanisms, and whether perinatal SA photoperiod would similarly reduce effort expenditure in a task relevant to everyday decision-making.

OBJECTIVES AND METHODS

We first tested male and female mice exposed to either gestational (E0-P0) or postnatal (E0-P28) SA photoperiod in the FST to determine whether the previously observed alteration was driven primarily by prenatal versus postnatal photoperiod. We then assessed whether SA gestational photoperiod reduces effortful choice behavior in the cross-species effort-based decision-making task (EBDMT) and whether any such deficit could be remediated by d-amphetamine (0.1 and 0.3 mg/kg, i.p.).

RESULTS

Mice exposed to prenatal, but not postnatal, SA photoperiod exhibited reduced FST immobility relative to controls and also demonstrated condition-dependently reduced preference for high-effort/high-reward versus low-effort/low-reward contingencies in the EBDMT. This effortful choice deficit was normalized by 0.1 mg/kg amphetamine.

CONCLUSIONS

These data: (1) suggest a greater contribution of gestational versus postnatal light conditions to the behavioral effects of perinatal SA photoperiod; and (2) implicate altered dopamine signaling in the behavioral phenotype of the SA-born mouse and possibly in the etiology of winter gestation-associated cases of psychiatric disease.

The Placebo Effect in Psychosis: Why It Matters and How to Measure It

Psychosis is characterized by unusual percepts and beliefs in the form of hallucinations and delusions. Antipsychotic medication, the primary treatment for psychosis, is often ineffective and accompanied by severe side effects, but research has not identified an effective alternative in several decades. One reason that clinical trials fail is that patients with psychosis tend to show a significant therapeutic response to inert control treatments, known as the placebo effect, which makes it difficult to distinguish drug effects from placebo effects. Conversely, in clinical practice, a strong placebo effect may be useful because it could enhance the overall treatment response. Identifying factors that predict large placebo effects could improve the future outlook of psychosis treatment. Biomarkers of the placebo effect have already been suggested in pain and depression, but not in psychosis. Quantifying markers of the placebo effect would have the potential to predict placebo effects in psychosis clinical trials. Furthermore, the placebo effect and psychosis may represent a shared neurocognitive mechanism in which prior beliefs are weighted against new sensory information to make inferences about reality. Examining this overlap could reveal new insights into the mechanisms underlying psychosis and indicate novel treatment targets. We provide a narrative review of the importance of the placebo effect in psychosis and propose a novel method to assess it.

Anxiolytic effects of Chrysanthemum morifolium Ramat Carbonisata-based carbon dots in mCPP-induced anxiety-like behavior in mice: a nature-inspired approach

Introduction: Anxiety disorders have emerged as a predominant health concern, yet existing pharmacological treatments for anxiety still present various challenges. Chrysanthemum morifolium Ramat Carbonisata (CMRC) has been utilized in China for approximately 400 years as a therapeutic intervention for anxiety disorders. In this study, a novel type of carbon dots derived from the decoction of Chrysanthemum morifolium Ramat Carbonisata (CMRC-CDs) was identified and isolated, and their morphological structure and functional groups were characterized. Furthermore, the effects of CMRC-CDs on m-chlorophenylpiperazine (mCPP)-induced anxiety-like behaviour in mice were examined and quantified. In order to investigate the potential mechanisms of their anxiolytic effects, concentrations of hypothalamic-pituitary-adrenal (HPA) axis hormones, amino acid neurotransmitters, and monoamine neurotransmitters were measured. Methods: In this study, we synthesized CMRC-CDs and evaluated their potential anti-anxiety effects in a controlled experiment involving 48 male ICR mice. The mice were randomly divided into six groups, treated with CMRC-CDs at different doses for 14 days, and subjected to Open-Field (OF) and Elevated Plus Maze (EPM) tests. Post-behavioral evaluations, blood samples and brain tissues were collected for neurotransmitter and Hypothalamic-Pituitary-Adrenal (HPA) axis hormone quantification via ELISA. Additionally, cytotoxicity of CMRC-CDs was assessed using a Cell Counting Kit-8 (CCK-8) assay on RAW 264.7 cells. Results and Discussion: CMRC-CDs were spherical and homogeneously dispersed, with diameters ranging from 1.4 to 4.0 nm and an abundance of chemical groups on their surface. In the open-field (OF) test, mice pre-treated with CMRC-CDs demonstrated an increased proportion of time spent in the central area and a higher frequency of entries into the central area. In the elevated plus maze (EPM) test, mice pre-treated with CMRC-CDs exhibited a greater number of entries into the open arm and an extended duration spent in the open arm. CMRC-CDs were observed to decrease serum concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and corticosterone (CORT). Furthermore, CMRC-CDs were found to increase γ-aminobutyric acid (GABA) and 5-hydroxytryptamine (5-HT) levels, while concurrently reducing glutamic acid (Glu) concentrations in brain tissue. CMRC-CDs demonstrated anxiolytic effects, which may be attributed to their modulation of hormones and neurotransmitters. This finding suggests the potential therapeutic value of CMRC-CDs in the clinical treatment of anxiety disorders.

Anxiolytic-like effect of Suanzaoren-Wuweizi herb-pair and evidence for the involvement of the monoaminergic system in mice based on network pharmacology

BACKGROUND

Suanzaoren-Wuweizi herb-pair (SWHP), composed of Zizyphi Spinosi Semen (Suanzaoren in Chinese) and Schisandrae Chinensis Fructus (Wuweizi in Chinese), is a traditional herbal formula that has been extensively used for the treatment of insomnia. The study aimed to explore the targets and signal pathways of Suanzaoren-Wuweizi (S-W) in the treatment of anxiety by network pharmacology, and to verify the pharmacodynamics and key targets of SWHP in mice.

METHODS

The Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) as well as literature mining were used to obtain the main chemical ingredients of Suanzaoren and Wuweizi. The SwissTargetPrediction platform was used to predict drug-related targets. The GeneCards, TTD, DisGeNET and OMIM databases were used to obtain potential targets for the treatment of anxiety with the chemical components of S-W. Drug-disease intersection genes were selected, and a protein-protein interaction (PPI) network was constructed using STRING. The core targets of S-W in the treatment of anxiety were selected according to the topological parameters, and GO functional enrichment as well as KEGG pathways enrichment analyses were performed for potential targets. The relationship network of the "drug-active ingredient-disease-target-pathway" was constructed through Cytoscape 3.8.0. The pharmacodynamics of SWHP in the treatment of anxiety was evaluated by the elevated plus maze (EPM), the light/dark box test (LDB) and the open field test (OFT). The mechanisms were examined by measuring monoamine neurotransmitters in brain of mice.

RESULTS

The results showed that there were 13 active ingredients for the treatment of anxiety in the network. This includes sanjoinenine, swertisin, daucosterol, schizandrer B, wuweizisu C and gomisin-A. Additionally, there were 148 targets, such as AKT1, TNF, SLC6A4, SLC6A3, EGFR, ESR1, HSP90AA1, CCND1, and DRD2, mainly involved in neuroactive ligand-receptor interactions, the Serotonergic synapse pathway and the cAMP signaling pathway. After 1 week of treatment, SWHP (2 and 3 g/kg) induced a significant increase on the percentage of entries into and time spent on the open arms of the EPM. In the LDB test, SWHP exerted anxiolytic-like effect at 2 g/kg. In the open-field test, SWHP (2 g/kg) increased the number of central entries and time spent in central areas. The levels of brain monoamines (5-HT and DA) and their metabolites (5-HIAA, DOPAC) were decreased after SWHP treatment.

CONCLUSIONS

The anti-anxiety effect of SWHP may be mediated by regulating 5-HT, DA and other signaling pathways. These findings demonstrated that SWHP produced an anxiolytic-like effect and the mechanism of action involves the serotonergic and dopaminergic systems, although underlying mechanism remains to be further elucidated.

Carbon Dots Derived from Os Draconis and Their Anxiolytic Effect

Background

At present, people are susceptible to developing depression and anxiety disorders in response to stress. However, there is no specific medicine for anxiety. Os Draconis (OD, named "Long gu" in Chinese) are fossilized bones that have been used in traditional Chinese medicine to treat neurological diseases for thousands of years. Thus, we conducted this study to determine the biological basis for the anxiolytic effect of OD.

Methods

In this study, novel carbon dots (OD-CDs) from OD decoctions were discovered and separated. OD-CDs were anatomized using nanomaterials characterization methods to characterize the morphological structure, optical properties, and functional group properties. Four behavioural tests were conducted to observe the behavioural activities of mice, including the open field test (OFT), light/dark box test (LDT), elevated plus maze test (EPMT), and novelty-suppressed feeding test (NSFT), to determine its anxiolytic effects. Moreover, we assessed the possible mechanisms of the OD-CDs by detecting hormones associated with the hypothalamic-pituitary-adrenal (HPA) axis.

Results

OD-CDs were spherical and monodispersed with a narrow size distribution between 1 and 5 nm and had a yield of 3.67%. OD-CDs increased the activity time of mice in the central zone in the OFT. The mice in the experimental group showed more frequent activity in the light compartment and the open arms, in LDT and EPMT, respectively. In addition, OD-CDs shortened the feeding latency in the NSFT. Furthermore, the results after OD-CDs intervention showed a significant increase in serum serotonin (5-HT) and norepinephrine (NE). In addition, the concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ATCH), and corticosterone (CORT) were decreased.

Conclusion

These results demonstrate a definite anxiolytic effect of OD-CDs and reveal the possible mechanism of action of OD-CDs' anxiolytic effect, which supports the research of OD for neurological disorders and a promising new trend of therapeutic approach and drug development.

Engaging endogenous opioid circuits in pain affective processes

The pervasive use of opioid compounds for pain relief is rooted in their utility as one of the most effective therapeutic strategies for providing analgesia. While the detrimental side effects of these compounds have significantly contributed to the current opioid epidemic, opioids still provide millions of patients with reprieve from the relentless and agonizing experience of pain. The human experience of pain has long recognized the perceived unpleasantness entangled with a unique sensation that is immediate and identifiable from the first-person subjective vantage point as "painful." From this phenomenological perspective, how is it that opioids interfere with pain perception? Evidence from human lesion, neuroimaging, and preclinical functional neuroanatomy approaches is sculpting the view that opioids predominately alleviate the affective or inferential appraisal of nociceptive neural information. Thus, opioids weaken pain-associated unpleasantness rather than modulate perceived sensory qualities. Here, we discuss the historical theories of pain to demonstrate how modern neuroscience is revisiting these ideas to deconstruct the brain mechanisms driving the emergence of aversive pain perceptions. We further detail how targeting opioidergic signaling within affective or emotional brain circuits remains a strong avenue for developing targeted pharmacological and gene-therapy analgesic treatments that might reduce the dependence on current clinical opioid options.

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.

Morphine-Conditioned Placebo Analgesia in Female and Male Rats with Chronic Neuropathic Pain: c-Fos Expression in the Rostral Ventromedial Medulla

Placebo analgesia has great potential to overcome the inadequacies of current drug therapies to treat conditions of chronic pain. The rostral ventromedial medulla (RVM) has been implicated as a critical relay in the antinociceptive pathway underpinning placebo analgesia in humans. We developed a model of opiate-conditioned placebo analgesia in rats with neuropathic injury to identify medullary nuclei active during placebo analgesia. Using female and male rats the degree of thermal allodynia was first determined following nerve injury, and a pharmacological conditioning procedure, pairing contextual cues with the experience of morphine-induced analgesia, was used to elicit placebo analgesic reactions. This protocol revealed clear subpopulations of placebo reactors (36% of males, 25% of females) and non-reactors in proportions similar to those reported in human studies. We detected injury-specific c-Fos expression in the gracile nucleus and morphine-specific c-Fos expression in the serotonergic midline raphe nuclei and the caudal nuclei of the solitary tract. However, c-Fos expression did not differ between placebo reactors and non-reactors in either serotonergic or non-serotonergic neurons of the RVM. Despite a subpopulation of rats demonstrating placebo reactions, we found no evidence for enhanced activity in the nuclei from which the classical RVM → spinal cord descending analgesic pathways emerge.

Hypnotic activities of Zao Ren An Shen capsule, a traditional Chinese medicine, in an anxiety-like mouse model

PURPOSE

Zao Ren An Shen capsule (ZRASC) which is composed of three kinds of traditional Chinese herbs is a popular Chinese medicine for the treatment of insomnia. This study investigated the hypnotic effect of ZRASC in an anxiety-like mouse model.

METHODS

We determined the role of ZRASC in anxiety and co-morbid insomnia using electroencephalogram and electromyogram recordings. Anxiety-like behaviors were tested by using the open-field, light/dark box, or elevated plus-maze in mice. Immunohistochemical techniques were employed to reveal the mechanism by which ZRASC regulated anxiety and insomnia.

RESULTS

ZRASC at 680 mg/kg prolonged the time spent in the central area, open arms area, and light box by 1.9, 2.3, and 1.7-fold respectively, compared with the vehicle control group in immobilization stress (IMS) mice. ZRASC at 680 mg/kg given at 08:00 h increased the amount of non-rapid eye movement sleep by 1.4-fold in a 2-h period after dosing in IMS mice. However, it did not alter the sleep-wake behaviors in normal mice. Immunohistochemistry showed that IMS increased c-Fos expression in the neurons of the stria terminalis and tuberomammillary nucleus by 1.8 and 1.6-fold, respectively. In addition, ZRASC (680 mg/kg) reversed the IMS-induced c-Fos expression.

CONCLUSIONS

Our results suggest that ZRASC is an effective therapeutic strategy for both anxiety disorder and sleep disturbances in an anxiety-like mouse model.

Personality Differences of Brain Networks in Placebo Analgesia and Nocebo Hyperalgesia: A Psychophysiological Interaction (PPI) Approach in fMRI

It is generally believed that the placebo response can elicit an analgesic effect, whilst the nocebo response can elicit a hyperalgesia effect in pain. Placebo analgesia and nocebo hyperalgesia effects are increasing concerns for researchers. Growing evidence suggests personality differences have an impact on both placebo and nocebo effects. However, previous studies have not reached a unified conclusion. We designed this study to explore the personality differences of functional magnetic resonance imaging (fMRI) signals in placebo response and nocebo response by using psychophysiological interaction (PPI) analysis. 30 healthy subjects underwent conditioning induction training to establish expectations of placebo effect and nocebo effect, and then, all subjects completed the following experimental procedures: (1) baseline scanning, (2) acute pain model establishment, (3) pain status scanning, and (4) pseudorandom scanning of block design of placebo response or nocebo response. Behavioral data were collected after each scan. The results of this study showed that (1) there were significant differences of VAS placebo intervention between the extrovert group and the introvert group (p = 0.004); (2) there were significant differences of VAS nocebo intervention between the extrovert group and the introvert group (p = 0.011); (3) there were significant differences between the VAS placebo intervention and VAS pain status (baseline) in both the extrovert group (p < 0.001) and the introvert group (p = 0.001); (4) there were significant differences between the VAS nocebo intervention and VAS pain status (baseline) in both the extrovert group (p = 0.008) and the introvert group (p < 0.001). Moreover, there were significant differences in the brain network for placebo and nocebo responses between different personalities. We found that (1) deactivation differences of the pain-related network and limbic system play an important role in personality differences associated with placebo analgesia and (2) differences of control of anxiety and activation of dorsolateral prefrontal cortex may cause the personality differences observed in nocebo hyperalgesia.

Anxiolytic Effect of Alcohol-Water Extracted Suanzaoren-Wuweizi Herb-Pair by Regulating ECS-BDNF-ERK Signaling Pathway Expression in Acute Restraint Stress Male Rats

Herb-pairs are the basic units of composition in Chinese herbal formulae, where the bridge linking Chinese medicine and prescription consists of two Chinese medicine herbs. The Suanzaoren-Wuweizi herb-pair (SWHP) is commonly used as a sedative or tranquilizer. SWHP has been demonstrated to exert an antianxiety effect in animal models of anxiety. However, little information about its mechanism is available and the effects of SWHP have not been investigated. This study examined the effects of SWHP on ameliorating anxiety-like behaviors by regulating endocannabinoids system (ECS)-brain-derived neurotrophic factor (BDNF)-extracellular regulated protein kinases (ERK) signaling pathway expression, induced by restraint stress (RS) procedures. The antianxiety effects of SWHP on RS rats were then examined through the open-field test (OF) and the elevated plus maze test (EPM). The concentration of BNDF, ERK1/2, p-ERK1/2, cAMP-response element binding protein (CREB), and p-CREB expression in the prefrontal cortex and hippocampus of the rats was then measured by western blot. The number of positive cells of CB1 and CB2 in the rats' hippocampus CA1 region was measured by immunohistochemistry. These results gave compelling evidence that SWHP could modify anxiety-like behaviors of RS rats through regulation of the ECS-BDNF-ERK signaling pathway. Our study demonstrated that SWHP improved anxiety-like behaviors in RS rat models by regulating the ECS-BDNF-ERK signaling pathway. The findings indicate that SWHP may have a therapeutic application in the RS model of anxiety disorder, which proposes a potential new direction for research into anxiety disorders regarding mechanisms and the development of novel antianxiety drugs.

Classical conditioning of antidepressant placebo effects in mice

INTRODUCTION

Placebo effects in human clinical trials for depression treatment are robust and often comparable to drug effects. Placebo effects are traditionally difficult to study in rodents due to the slow-onset action of classical antidepressant drugs. We hypothesized that the rapid antidepressant actions of ketamine would allow modeling antidepressant placebo effects in rodents.

METHODS

Male and female CD-1 mice received either ketamine or saline injections with concomitant exposure to specific environmental conditioning stimuli, for a total of three drug/conditioning sessions each 2 weeks apart. Two weeks later, during an evocation phase, mice were exposed to the drug-paired conditioning stimuli or no conditioned stimuli followed by testing for motor stimulatory actions and antidepressant-like effects using the forced swim test. Negative (no ketamine administration at any time) and positive (acute ketamine administration prior to evocation testing) control groups were included as comparators.

RESULTS

Both male and female mice exhibited increased locomotor activity following ketamine administration during the conditioning phase, which was not observed following exposure to the conditioning stimuli. Exposure to the conditioning stimuli previously paired with ketamine, similar to an acute ketamine administration, reduced immobility time in the forced swim test both 1 and 24 h after administration in male, but not female, mice.

CONCLUSIONS

These results represent the first evidence of antidepressant-like placebo-conditioned effects in an animal model. The developed approach can be used as a model to explore the neurobiological mechanisms of placebo effects, their possible sexually dimorphic effects, and relevance to mechanisms underlying antidepressant action.

Failure of Placebo Analgesia Model in Rats with Inflammatory Pain

With the shifting role of placebos, there is a need to develop animal models of placebo analgesia and elucidate the mechanisms underlying the effect. In the present study, male Sprague-Dawley rats with chronic inflammatory pain caused by complete Freund's adjuvant (CFA) underwent a series of conditioning procedures, in which morphine was associated with different cues, but they failed to induce placebo analgesia. Then, conditioning with the conditioned place preference apparatus successfully induced analgesic expectancy and placebo analgesia in naïve rats but only induced analgesic expectancy and no analgesic effect in CFA rats. Subsequently, we found enhanced c-fos expression in the nucleus accumbens and reduced expression in the anterior cingulate cortex in naïve rats while c-fos expression in the anterior cingulate cortex in CFA rats was not altered. In summary, the behavioral conditioning model demonstrated the difficulty of establishing a placebo analgesia model in rats with a pathological condition.

Role of placebo effects in pain and neuropsychiatric disorders

The placebo (and the nocebo) effect is a powerful determinant of health outcomes in clinical disease treatment and management. Efforts to completely eradicate placebo effects have shifted dynamically, as increasingly more researchers are tuned to the potentially beneficial effects of incorporating those uncontrollable placebo effects into clinical therapeutic strategies. In this review, we highlight the major findings from placebo research, elucidating the main neurobiological systems and candidate determinants of the placebo phenomenon, and illustrate a perspective that can effectively frame future research on the topic. Finally, we issue a call for increased research on the efficacy of therapeutic strategies that incorporate placebo "tools," and argue that clinical trials of the placebo response in neuropsychiatric diseases and disorders has important and far-reaching translational and clinical relevance.

The Placebo Effect in Pain Therapies

Pharmacological strategies for pain management have primarily focused on dampening ascending neurotransmission and on opioid receptor-mediated therapies. Little is known about the contribution of endogenous descending modulatory systems to clinical pain outcomes and why some patients are mildly affected while others suffer debilitating pain-induced dysfunctions. Placebo effects that arise from patients' positive expectancies and the underlying endogenous modulatory mechanisms may in part account for the variability in pain experience and severity, adherence to treatment, distinct coping strategies, and chronicity. Expectancy-induced analgesia and placebo effects in general have emerged as useful models to assess individual endogenous pain modulatory systems. Different systems and mechanisms trigger placebo effects that highly impact pain processing, clinical outcomes, and sense of well-being. This review illustrates critical elements of placebo mechanisms that inform the methodology of clinical trials, the discovery of new therapeutic targets, and the advancement of personalized pain management.

Placebo Analgesia in Rodents: Current and Future Research

The investigation of placebo effects in animal pain models has received less attention than human research. This may be related to a number of difficulties, including the fact that animals lack the ability to use language and establish expectancies verbally, that animals cannot report and rate the extent to which they experience pain, and the inadequacy of current models of pain. Here, we describe the relatively small number of studies that have been published, communicating the opportunities and excitement of this research. We critically discuss pitfalls and limitations with the hope that this will advance future animal placebo-related research.

Mechanisms of placebo analgesia: A dual-process model informed by insights from cross-species comparisons

Placebo treatments are pharmacologically inert, but are known to alleviate symptoms across a variety of clinical conditions. Associative learning and cognitive expectations both play important roles in placebo responses, however we are just beginning to understand how interactions between these processes lead to powerful effects. Here, we review the psychological principles underlying placebo effects and our current understanding of their brain bases, focusing on studies demonstrating both the importance of cognitive expectations and those that demonstrate expectancy-independent associative learning. To account for both forms of placebo analgesia, we propose a dual-process model in which flexible, contextually driven cognitive schemas and attributions guide associative learning processes that produce stable, long-term placebo effects. According to this model, the placebo-induction paradigms with the most powerful effects are those that combine reinforcement (e.g., the experience of reduced pain after placebo treatment) with suggestions and context cues that disambiguate learning by attributing perceived benefit to the placebo. Using this model as a conceptual scaffold, we review and compare neurobiological systems identified in both human studies of placebo analgesia and behavioral pain modulation in rodents. We identify substantial overlap between the circuits involved in human placebo analgesia and those that mediate multiple forms of context-based modulation of pain behavior in rodents, including forebrain-brainstem pathways and opioid and cannabinoid systems in particular. This overlap suggests that placebo effects are part of a set of adaptive mechanisms for shaping nociceptive signaling based on its information value and anticipated optimal response in a given behavioral context.

The Cognitive Neuroscience of Placebo Effects: Concepts, Predictions, and Physiology

Placebos have been used ubiquitously throughout the history of medicine. Expectations and associative learning processes are important psychological determinants of placebo effects, but their underlying brain mechanisms are only beginning to be understood. We examine the brain systems underlying placebo effects on pain, autonomic, and immune responses. The ventromedial prefrontal cortex (vmPFC), insula, amygdala, hypothalamus, and periaqueductal gray emerge as central brain structures underlying placebo effects. We argue that the vmPFC is a core element of a network that represents structured relationships among concepts, providing a substrate for expectations and a conception of the situation-the self in context-that is crucial for placebo effects. Such situational representations enable multidimensional predictions, or priors, that are combined with incoming sensory information to construct percepts and shape motivated behavior. They influence experience and physiology via descending pathways to physiological effector systems, including the spinal cord and other peripheral organs.

Brain Mechanisms of the Placebo Effect: An Affective Appraisal Account

Placebos are sham medical treatments. Nonetheless, they can have substantial effects on clinical outcomes. Placebos depend on a person's psychological and brain responses to the treatment context, which influence appraisals of future well-being. Appraisals are flexible cognitive evaluations of the personal meaning of events and situations that can directly impact symptoms and physiology. They also shape associative learning processes by guiding what is learned from experience. Appraisals are supported by a core network of brain regions associated with the default mode network involved in self-generated emotion, self-evaluation, thinking about the future, social cognition, and valuation of rewards and punishment. Placebo treatments for acute pain and a range of clinical conditions engage this same network of regions, suggesting that placebos affect behavior and physiology by changing how a person evaluates their future well-being and the personal significance of their symptoms.

Relieving pain using dose-extending placebos: a scoping review

Placebos are often used by clinicians, usually deceptively and with little rationale or evidence of benefit, making their use ethically problematic. In contrast with their typical current use, a provocative line of research suggests that placebos can be intentionally exploited to extend analgesic therapeutic effects. Is it possible to extend the effects of drug treatments by interspersing placebos? We reviewed a database of placebo studies, searching for studies that indicate that placebos given after repeated administration of active treatments acquire medication-like effects. We found a total of 22 studies in both animals and humans hinting of evidence that placebos may work as a sort of dose extender of active painkillers. Wherever effective in relieving clinical pain, such placebo use would offer several advantages. First, extending the effects of a painkiller through the use of placebos may reduce total drug intake and side effects. Second, dose-extending placebos may decrease patient dependence. Third, using placebos along with active medication, for part of the course of treatment, should limit dose escalation and lower costs. Provided that nondisclosure is preauthorized in the informed consent process and that robust evidence indicates therapeutic benefit comparable to that of standard full-dose therapeutic regimens, introducing dose-extending placebos into the clinical arsenal should be considered. This novel prospect of placebo use has the potential to change our general thinking about painkiller treatments, the typical regimens of painkiller applications, and the ways in which treatments are evaluated.

The placebo effect: From concepts to genes

Despite its initial treatment as a nuisance variable, the placebo effect is now recognized as a powerful determinant of health across many different diseases and encounters. This is in light of some remarkable findings ranging from demonstrations that the placebo effect significantly modulates the response to active treatments in conditions such as pain, anxiety, Parkinson's disease, and some surgical procedures. Here, we review pioneering studies and recent advances in behavioral, neurobiological, and genetic influences on the placebo effect. Consistent with recent conceptualizations, the placebo effect is presented as the product of a general expectancy learning mechanism in which verbal, conditioned, and social cues are centrally integrated to change behaviors and outcomes. Examples of the integration of verbal and conditioned cues, such as instructed reversal of placebo effects are also incorporated into this model. We discuss neuroimaging studies that have identified key brain regions and modulatory mechanisms underlying placebo effects using well-established behavioral paradigms. Finally, we present a synthesis of recent genetics studies on the placebo effect, highlighting a promising link between genetic variants in the dopamine, opioid, serotonin, and endocannabinoid pathways and placebo responsiveness. Greater understanding of the behavioral, neurobiological, and genetic influences on the placebo effect is critical for evaluating medical interventions and may allow health professionals to tailor and personalize interventions in order to maximize treatment outcomes in clinical settings.

The neuroscience of placebo effects: connecting context, learning and health

Placebo effects are beneficial effects that are attributable to the brain-mind responses to the context in which a treatment is delivered rather than to the specific actions of the drug. They are mediated by diverse processes--including learning, expectations and social cognition--and can influence various clinical and physiological outcomes related to health. Emerging neuroscience evidence implicates multiple brain systems and neurochemical mediators, including opioids and dopamine. We present an empirical review of the brain systems that are involved in placebo effects, focusing on placebo analgesia, and a conceptual framework linking these findings to the mind-brain processes that mediate them. This framework suggests that the neuropsychological processes that mediate placebo effects may be crucial for a wide array of therapeutic approaches, including many drugs.

Post-training corticosterone inhibits the return of fear evoked by platform stress and a subthreshold conditioning procedure in Sprague-Dawley rats

The return of fear is an important issue in anxiety disorder research. Each time a fear memory is reactivated, it may further strengthen overactivation of the fear circuit, which may contribute to long-term maintenance of the fear memory. Recent evidence indicates that glucocorticoids may help attenuate pathological fear, but its role in the return of fear is unclear. In the present study, systemic corticosterone (CORT; 25mg/kg) administration 1h after fear conditioning did not impair the consolidation process but significantly suppressed the return of fear evoked by a subthreshold conditioning (SC) procedure and elevated platform (EP) stress. Compared with the SC-induced return of fear, acute stress-induced return was state-dependent. In addition, post-training CORT treatment increased the adrenocorticotropic response after EP stress, which indicates that the drug-induced suppression of the return of fear may possibly derive from its regulation effect of the hypothalamic-pituitary-adrenal axis reactivity to stress. These results suggest that post-training CORT administration may help inhibit the return of fear evoked by EP or SC stress. The possible mechanisms involved in the high-dose CORT-induced suppression of the SC- and EP-induced return of fear are discussed.

The elusive rat model of conditioned placebo analgesia

Recent research on human placebo analgesia has suggested the need for rodent models to further elucidate the neural substrates of the placebo effect. This series of 3 experiments therefore was performed in an attempt to develop a model of placebo analgesia in rats. In each study, female Sprague-Dawley rats received an L5 spinal nerve ligation to induce a neuropathic pain condition. Each rat then underwent a 4-day conditioning procedure in which an active analgesic drug or its vehicle (unconditioned stimulus) was associated with the following cues (conditioned stimuli): novel testing room (environmental), vanilla scent cue (olfactory), dim incandescent lighting (visual), restraint procedure/injection (tactile), and time of day and injection-test latency (temporal). The analgesics for each experiment were as follows: Experiment 1 used 90 mg/kg gabapentin, experiment 2 used 3mg/kg loperamide hydrochloride, and experiment 3 used 6 mg/kg morphine sulfate. On the following test day, half of the animals received the opposite treatment, resulting in 4 conditioning manipulations: drug/drug, drug/vehicle, vehicle/drug, and vehicle/vehicle. Nociceptive thresholds were assessed with the mechanical paw withdrawal threshold test each day after the conditioning procedure. In all 3 experiments, no significant differences were detected on test day between control and placebo groups, indicating a lack of a conditioned placebo analgesic response. Our results contrast with prior research that implies the existence of a reliable and robust response to placebo treatment. We conclude that placebo analgesia in rats is not particularly robust and that it is difficult to achieve using conventional procedures and proper experimental design.

Placebo, nocebo, and learning mechanisms

Recent substantial laboratory and theoretical research hints for different learning mechanisms regulating the formation of placebo and nocebo responses. Moreover, psychological and biological variants may play a role as modulators of learning mechanisms underlying placebo and nocebo responses. In this chapter, we present pioneering and recent human and nonhuman research that has impressively increased our knowledge of learning mechanisms in the context of placebo and nocebo effects across different physiological processes and pathological conditions.

Mechanisms and therapeutic implications of the placebo effect in neurological and psychiatric conditions

The power of a placebo to effect clinically meaningful neurobiological change comparable to pharmacological therapies has been demonstrated, although the mechanisms are not fully understood. Predicting placebo responsiveness has only recently received more attention, but psychological disposition, contextual and biological factors are now known to dramatically affect a person's susceptibility to the placebo effect. The placebo effect depends upon expectancies that can be modified in a number of ways, including conditioning through explicit or implicit learned associations. Based on the dopaminergic response to anticipation of benefit in Parkinson's disease, it was suggested that the placebo effect can be seen as analogous to the expectation of reward. Dopaminergic pathways have since been implicated in the placebo response in pain and depression. Additionally, endogenous opioid release is known to mediate many forms of placebo analgesia. We provide an overview of the mechanisms and the therapeutic implications of the placebo effect in neurological and psychiatric conditions. We include evidence for detrimental effects arising from seemingly inert interventions, termed the 'nocebo effect.' Neuroimaging has critically advanced the study of the placebo effect and provides some of the strongest evidence for the mechanisms of this phenomenon prevalent across an array of human health-related circumstances. This review specifically focuses on mechanisms of the placebo effect in the three conditions that have most significantly demonstrated this effect and for which a plausible physiological basis can be identified: pain, PD and depression. Other neurological and psychiatric diseases reviewed include multiple sclerosis, Huntington's disease, Alzheimer's disease, schizophrenia and epilepsy.

The opioid placebo analgesia is mediated exclusively through μ-opioid receptor in rat

Placebo analgesia is one of the most robust and best-studied placebo effects. Recent researches suggest that placebo analgesia activated the μ-opioid receptor signalling in the human brain. However, whether other opioid receptors are involved in the placebo analgesia remains unclear. We have previously evoked placebo responses in mice (Guo et al. 2010, 2011) and these mice may serve as a model for investigating placebo analgesia. In the present study, we tried to explore the site of action and types of opioid receptors involved in placebo response. Male Sprague-Dawley rats were trained with 10 mg/kg morphine for 4 d to establish the placebo analgesia model. This placebo analgesia can be blocked by injection of 5 mg/kg dose naloxone or by microinjection with naloxone (1, 3 or 10 μg/rat) into rostral anterior cingulate cortex (rACC). Then, animals were tested after intra-rACC microinjection of D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP, a selective μ-opioid receptor antagonist) or naltrindole (NTI, a highly selective δ-opioid receptor antagonist) or nor-binaltorphimine (nor-BNI, a highly selective κ-opioid receptor antagonist). Our results showed that CTOP, but not NTI or nor-BNI, could reduce the pain threshold in placebo analgesia rats. It may be concluded that rACC is the key brain region involved in placebo analgesia and the opioid placebo analgesia is mediated exclusively through μ-opioid receptor in rat.

Evaluation of anxiolytic activity of compound Valeriana jatamansi Jones in mice

Background

Compound Valeriana jatamansi Jones is a formula for treating anxiety-related diseases in the clinic, which is composed of Valeriana jatamansi Rhizoma et Radix, Ziziphi Spinosae Semen, Albiziae Cortex and Junci Medulla. The purpose of this study was to explore the anxiolytic properties of this compound in mice.

Methods

Male ICR mice were treated with compound Valerianae Jatamansi Jones (1.2 g/kg, 2.4 g/kg, 4.8 g/kg), saline, diazepam (2 mg/kg) orally for 10 days and then exposed to elevated maze-plus (EPM) and light–dark box (LDB). The effects of the compound on spontaneous activity were evaluated by locomotor activity test. We further investigated the mechanism of action underlying the anxiolytic-like effect of compound by pre-treating animals with antagonists of benzodiazepine (flumazenil, 3mg/kg) prior to evaluation using EPM and LDB.

Results

Compound Valerianae Jatamansi Jones (2.4, 4.8 g/kg, p.o.) significantly increased entries (P<0.05) into and time spent (P<0.05) on the open arms of the EPM, and number of transitions (P<0.05) and time spent (P<0.05) in the light compartment of the LDB. However, the anxiolytic-like effects of compound were significantly reduced by pre-treatment with flumazenil (P>0.05). In addition, compound Valerianae Jatamansi Jones treatment didn’t affect the spontaneous activity in mice (P> 0.05).

Conclusions

The present study supports the hypothesis that compound Valeriana jatamansi Jones exert anxiolytic action but no sedative effects in mice and that this effect might be mediated by benzodiazepine receptors.

Anxiolytic-like effects of compound zhi zhu xiang in rats

The purpose of this study was to determine whether compound zhi zhu xiang (CZZX) exerts anxiolytic-like effects in rats. The animals were orally administered CZZX (0.75, 1.5, and 3 g/kg daily) for 10 days and tested in the elevated plus maze (EPM), Vogel conflict test (VCT), and open field. Repeated treatment with CZZX (3 g/kg/day, p.o.) significantly increased the percentage of both entries into and time spent on the open arms of the EPM compared with saline controls. In the VCT, repeated treatment with CZZX (1.5 and 3 g/kg/day, p.o.) significantly increased the number of punished licks. The drug did not change the total entries into the open arms of the EPM or interfere with water consumption or nociceptive threshold, discarding potential confounding factors in the two tests. In the open field, locomotion was not reduced, discarding the possible sedative effect of CZZX. In the binding assay, the binding of [(3)H] Ro 15-1788 (flumazenil) to the benzodiazepine binding site in washed crude synaptosomal membranes from rat cerebral cortex was affected by CZZX. These data indicate an anxiolytic-like profile of action for CZZX without sedative side effects, and this activity may be mediated by benzodiazepine binding site modulation at γ-aminobutyric acid-A receptors.

Isolation and biological activity of triglycerides of the fermented mushroom of Coprinus Comatus

BACKGROUND

Although many physiological functions of Coprinus comatus have been reported, there has been no report on the antinociceptive activity of Coprinus comatus. Therefore, the objective of the present study is to demonstrate the production, isolation, and biological properties of triglycerides (TFC) of the fermented mushroom of Coprinus comatus.

METHODS

The effects of TFC on cytokines levels, total antioxidant activity, antinociceptive effects in vivo, LD50 and tactile hyperalgesia were analyzed respectively.

RESULTS

TFC treatment decreased the levels of cytokines and total antioxidant status (TAOS) and inhibited the acetic acid-induced abdominal constrictions in mice. In addition, TFC reduced CFA-induced tactile hyperalgesia in a dose-dependent manner and the LD50 of TFC was determined to be 400 mg/kg. However, TFC did not significantly inhibit the reaction time to thermal stimuli in the hot-plate test.

CONCLUSIONS

TFC showed anti-inflammatory, antioxidant, peripheral antinociceptive and antihyperalgesic activity in various models of inflammatory pain. The data suggest that TFC may be a viable treatment option for inflammatory pain.