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Schwarting RKW, Wöhr M, Engler H, Sungur AÖ, Schedlowski M. 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. Neurosci Biobehav Rev 2024; 162:105721. [PMID: 38754716 DOI: 10.1016/j.neubiorev.2024.105721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2024] [Revised: 04/26/2024] [Accepted: 05/10/2024] [Indexed: 05/18/2024]
Abstract
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.
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Affiliation(s)
- Rainer K W Schwarting
- Philipps-University of Marburg, Faculty of Psychology, Experimental and Biological Psychology, Behavioral Neuroscience, Marburg D-35032, Germany; Center for Mind, Brain and Behavior, Marburg D-35032, Germany
| | - Markus Wöhr
- Philipps-University of Marburg, Faculty of Psychology, Experimental and Biological Psychology, Behavioral Neuroscience, Marburg D-35032, Germany; Center for Mind, Brain and Behavior, Marburg D-35032, Germany; KU Leuven, Faculty of Psychology and Educational Sciences, Research Unit Brain and Cognition, Laboratory of Biological Psychology, Social and Affective Neuroscience Research Group, Leuven B-3000, Belgium; KU Leuven, Leuven Brain Institute, Leuven B-3000, Belgium
| | - Harald Engler
- Institute of Medical Psychology and Behavioral Immunobiology, Center for Translational Neuro-, and Behavioral Sciences, University Hospital Essen, University of Duisburg-Essen, Essen D-45147, Germany
| | - A Özge Sungur
- Philipps-University of Marburg, Faculty of Psychology, Experimental and Biological Psychology, Behavioral Neuroscience, Marburg D-35032, Germany; Center for Mind, Brain and Behavior, Marburg D-35032, Germany; KU Leuven, Faculty of Psychology and Educational Sciences, Research Unit Brain and Cognition, Laboratory of Biological Psychology, Social and Affective Neuroscience Research Group, Leuven B-3000, Belgium; KU Leuven, Leuven Brain Institute, Leuven B-3000, Belgium
| | - Manfred Schedlowski
- Institute of Medical Psychology and Behavioral Immunobiology, Center for Translational Neuro-, and Behavioral Sciences, University Hospital Essen, University of Duisburg-Essen, Essen D-45147, Germany; Department of Clinical Neuroscience, Osher Center for Integrative Medicine, Karolinska Institutet, Stockholm 171 77, Sweden
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Totsch SK, Sorge RE. A novel investigation of placebo analgesia through social communication in mice. Behav Brain Res 2024; 459:114773. [PMID: 38000532 DOI: 10.1016/j.bbr.2023.114773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 11/08/2023] [Accepted: 11/20/2023] [Indexed: 11/26/2023]
Abstract
BACKGROUND AND AIMS In rodents, placebo analgesia is often investigated through direct conditioning of stimuli, but humans can experience placebo analgesia through expectation without experience. In this study, we sought to determine whether placebo analgesia could be elicited through social communication. METHODS Male and female mice were housed in pairs (designated "Active" and "Bystander") and tested for thermal thresholds on a hot plate (53 °C). Food restriction (1 hr/day) was implemented. The Active mouse was taken to a new cage with food dusted with cocoa (COC) or cinnamon (CINN). The Bystander mice were given regular chow in the home cage. After feeding, the Active mice were given morphine (5 mg/kg, SC) or saline and tested on the hot plate. After 5 pairings of a flavor and treatment (counterbalanced), Active mice were tested following access to a flavored food. Bystander mice were given their first direct exposure to a flavored food and tested on the hot plate. The protocol was repeated with naloxone (10 mg/kg, IP) administered prior to testing. Finally, mice were tested in a two-choice test with both flavored foods available. RESULTS Active mice showed a conditioned analgesic response to the morphine-paired flavor that was reduced by naloxone. Bystander mice showed a placebo analgesic response to their cagemate's morphine-paired flavor that was not significantly impacted by naloxone. Bystander mice spent more time in the chamber associated with their cagemate's morphine-paired flavor. CONCLUSIONS To our knowledge, this is the first investigation of placebo analgesia without direct conditioning, instead relying on social communication between mice. The lack of effect with naloxone pretreatment suggests an opioid-independent effect in the Bystander mice. Placebo analgesia in mice may be possible without direct conditioning to better model the effect of expectation of a novel analgesic in humans.
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Affiliation(s)
- Stacie K Totsch
- Department of Psychology, University of Alabama at Birmingham, United States
| | - Robert E Sorge
- Department of Psychology, University of Alabama at Birmingham, United States.
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Chen B, Goldstein N, Dziubek J, Zhao S, Harrahill A, Sundai A, Choi S, Prevosto V, Wang F. Reverse engineering placebo analgesia. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.12.579946. [PMID: 38405975 PMCID: PMC10888847 DOI: 10.1101/2024.02.12.579946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/27/2024]
Abstract
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.
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Boorman DC, Keay KA. Learning pain in context: Response-conditioned placebo analgesia and nocebo hyperalgesia in male rats with chronic neuropathic pain. Physiol Behav 2023; 263:114116. [PMID: 36773736 DOI: 10.1016/j.physbeh.2023.114116] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 01/23/2023] [Accepted: 02/08/2023] [Indexed: 02/11/2023]
Abstract
BACKGROUND Animal models of placebo analgesia and nocebo hyperalgesia have great potential to assist in the development of novel treatments for chronic pain that exploit or inhibit these phenomena. This study sought to elicit both conditioned placebo analgesia and conditioned nocebo hyperalgesia in rats with chronic neuropathic pain using non-pharmacological, contextual conditioning approaches, similar to those most often used in humans. METHODS Sciatic nerve-injured male Sprague-Dawley rats (n = 80), and sham controls (n = 16), underwent a conditioning procedure in which three different thermal stimulus intensities (4 °C, 20 °C or 30 °C) were paired with contextual cues. Injured hind paw withdrawal behaviours were used to determine pain sensitivity, and either conditioned analgesia or conditioned hyperalgesia was evoked by re-exposing the rats to the same context with either an increased or decreased thermal stimulus, respectively. RESULTS Stronger conditioned analgesia and conditioned hyperalgesia were seen when rats were conditioned in a more complex environment, highlighting the importance of context in these processes. Rats that did not undergo conditioning procedures showed fewer hind paw withdrawals, indicating a learned component to these pain behaviours. CONCLUSIONS Our data call attention to context and learning as two critical factors in the development of placebo and nocebo effects in male rodents with a neuropathic injury. Additionally, the response-conditioning model we present in this study affords better comparisons between human and animal studies, in particular for those seeking to identify commonalities in the neurobiological mechanisms of placebo and nocebo responses.
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Affiliation(s)
- Damien C Boorman
- School of Medical Sciences and the Brain and Mind Centre, The University of Sydney, New South Wales, 2006, Australia.
| | - Kevin A Keay
- School of Medical Sciences and the Brain and Mind Centre, The University of Sydney, New South Wales, 2006, Australia
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Psycho-Neuro-Endocrine-Immunological Basis of the Placebo Effect: Potential Applications beyond Pain Therapy. Int J Mol Sci 2022; 23:ijms23084196. [PMID: 35457014 PMCID: PMC9028312 DOI: 10.3390/ijms23084196] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 04/03/2022] [Accepted: 04/04/2022] [Indexed: 12/12/2022] Open
Abstract
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.
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Kimmey BA, McCall NM, Wooldridge LM, Satterthwaite T, Corder G. Engaging endogenous opioid circuits in pain affective processes. J Neurosci Res 2022; 100:66-98. [PMID: 33314372 PMCID: PMC8197770 DOI: 10.1002/jnr.24762] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 10/29/2020] [Accepted: 11/02/2020] [Indexed: 01/03/2023]
Abstract
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.
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Affiliation(s)
- Blake A. Kimmey
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA, Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA, Equal contributions
| | - Nora M. McCall
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA, Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA, Equal contributions
| | - Lisa M. Wooldridge
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA, Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Theodore Satterthwaite
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA, Lifespan Informatics and Neuroimaging Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Gregory Corder
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA, Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
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Boorman DC, Keay KA. Escalating morphine dosage fails to elicit conditioned analgesia in a preclinical chronic neuropathic pain model. Behav Pharmacol 2021; 32:479-486. [PMID: 34320522 DOI: 10.1097/fbp.0000000000000642] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Many people with chronic pain escalate their opioid dosage to counteract tolerance effects. A treatment regimen consisting of placebos admixed with opioids has been suggested as a possible therapeutic option that could reduce the harm of long-term opioid use. However, the analgesic efficacy of such a regimen requires further investigation before widespread adoption. We have recently reported that a 4-day pharmacological conditioning procedure, which paired morphine (6 mg/kg) with contextual cues, elicited placebo analgesia in subpopulations of male (35%) and female (25%) rats with sciatic nerve chronic constriction injury (CCI). Here, we investigated how an escalating morphine dosage during conditioning affects the incidence and strength of placebo analgesia. Forty-four male, Sprague-Dawley rats received CCI. Thirty-eight (86%) rats developed strong cold allodynia by day 6 post-surgery, as measured by hind paw withdrawal (HPW) behaviour on a 5°C cold plate (120 s). In this experiment, pharmacological conditioning consisted of an escalating morphine dose over 4 days (8/9/10/12 mg/kg). This dosing regimen produced strong reductions in HPW behaviour and counteracted the effects of morphine tolerance during conditioning. However, none of the rats given the placebo treatment (n = 12) demonstrated reductions in HPW behaviour when morphine was substituted for saline (i.e. placebo analgesia), but instead showed a strong behavioural response (rearing). These results demonstrate that a high, escalating dose of morphine failed to produce conditioned placebo analgesia in rats with CCI. It is possible that admixing placebos with opioids may be similarly ineffective in chronic pain patients when the opioids regimen is high or escalating.
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Affiliation(s)
- Damien C Boorman
- School of Medical Sciences (Neuroscience) and the Brain and Mind Centre, The University of Sydney, New South Wales, Australia
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Cho C, Deol HK, Martin LJ. Bridging the Translational Divide in Pain Research: Biological, Psychological and Social Considerations. Front Pharmacol 2021; 12:603186. [PMID: 33935700 PMCID: PMC8082136 DOI: 10.3389/fphar.2021.603186] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2020] [Accepted: 02/22/2021] [Indexed: 12/29/2022] Open
Abstract
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.
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Affiliation(s)
- Chulmin Cho
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Harashdeep K Deol
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Loren J Martin
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
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Morphine-Conditioned Placebo Analgesia in Female and Male Rats with Chronic Neuropathic Pain: c-Fos Expression in the Rostral Ventromedial Medulla. Neuroscience 2020; 457:51-73. [PMID: 33285237 DOI: 10.1016/j.neuroscience.2020.11.038] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 11/19/2020] [Accepted: 11/23/2020] [Indexed: 12/17/2022]
Abstract
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.
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Frumkin K. Behavioral Conditioning, the Placebo Effect, and Emergency Department Pain Management. J Emerg Med 2020; 59:303-310. [PMID: 32451185 DOI: 10.1016/j.jemermed.2020.04.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2019] [Revised: 03/26/2020] [Accepted: 04/08/2020] [Indexed: 10/24/2022]
Abstract
Animals and humans can be readily conditioned to associate a novel stimulus (often a unique taste) by pairing it with the effects of a drug or other agent. When later presented with the stimulus alone, their body's systems respond as if the drug or agent were given. The earliest clinical applications demonstrated both conditioned suppression and enhancement of immune processes. Unique benign stimuli, paired with chemotherapy, come to elicit T-cell suppression when administered alone. The beneficial immune responses to an antigen can be conditioned in the same manner. Further study of what came to be called "psychoneuroimmunology" led to the understanding that the familiar placebo effect, previously attributed to suggestion and expectation, is at least equally dependent on the same sorts of behavioral conditioning. The demonstrated ability to manipulate the immune system by a conditioned taste stimulus is, by definition, a placebo: a therapeutic effect caused by an inactive agent. The purpose of this analysis was to stimulate research in, and the application of, placebo-response conditioning to emergency medicine. Clinical and experimental studies confirm the usefulness of conditioned placebos in analgesia and in placebo-controlled dose reduction. Such conditioning paradigms demonstrate "one-trial learning," making them potentially useful in pain and addiction management within a single emergency department encounter.
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Affiliation(s)
- Kenneth Frumkin
- Emergency Medicine Department, Naval Medical Center, Portsmouth, Virginia
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Krimmel SR, Zanos P, Georgiou P, Colloca L, Gould TD. Classical conditioning of antidepressant placebo effects in mice. Psychopharmacology (Berl) 2020; 237:93-102. [PMID: 31422429 PMCID: PMC6954278 DOI: 10.1007/s00213-019-05347-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Accepted: 08/09/2019] [Indexed: 12/28/2022]
Abstract
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.
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Affiliation(s)
- Samuel R. Krimmel
- Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Neural and Pain Sciences, University of Maryland School of Dentistry, Baltimore, MD, USA.,Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Panos Zanos
- Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Polymnia Georgiou
- Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Luana Colloca
- Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Pain Translational Symptom Science, University of Maryland School of Nursing, Baltimore, MD, USA.,Department of Anesthesiology, University of Maryland School of Medicine, Baltimore, MD, USA.,Center to Advance Chronic Pain Research, University of Maryland, Baltimore, USA
| | - Todd D. Gould
- Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Pharmacology, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA.,Veterans Affairs Maryland Health Care System, Baltimore, MD, 21201, USA.,To whom correspondence should be addressed: Todd D. Gould, MD, Department of Psychiatry, University of Maryland School of Medicine, Rm. 936 MSTF, 685 W. Baltimore St., Baltimore, MD 21201, USA, Phone: (410) 706-5585,
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Gozani SN. Remote Analgesic Effects Of Conventional Transcutaneous Electrical Nerve Stimulation: A Scientific And Clinical Review With A Focus On Chronic Pain. J Pain Res 2019; 12:3185-3201. [PMID: 31819603 PMCID: PMC6885653 DOI: 10.2147/jpr.s226600] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 11/02/2019] [Indexed: 12/23/2022] Open
Abstract
BACKGROUND Transcutaneous electrical nerve stimulation (TENS) is a safe, noninvasive treatment for chronic pain that can be self-administered. Conventional TENS involves stimulation of peripheral sensory nerves at a strong, non-painful level. Following the original gate-control theory of pain, stimulation is typically near the target pain. As another option, remote stimulation may also be effective and offers potential advantages. OBJECTIVE This narrative review examines mechanisms underlying the remote analgesic effects of conventional TENS and appraises the clinical evidence. METHODS A literature search for English-language articles was performed on PubMed. Keywords included terms related to the location of TENS . Citations from primary references and textbooks were examined for additional articles. RESULTS Over 30 studies reported remote analgesic effects of conventional TENS. The evidence included studies using animal models of pain, experimental pain in humans, and clinical studies in subjects with chronic pain. Three types of remote analgesia were identified: at the contralateral homologous site, at sites distant from stimulation but innervated by overlapping spinal segments, and at unrelated extrasegmental sites. CONCLUSION There is scientific and clinical evidence that conventional TENS has remote analgesic effects. This may occur through modulation of pain processing at the level of the dorsal horn, in brainstem centers mediating descending inhibition, and within the pain matrix. A broadening of perspectives on how conventional TENS produces analgesia may encourage researchers, clinicians, and medical-device manufacturers to develop novel ways of using this safe, cost-effective neuromodulation technique for chronic pain.
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Yin XS, Yang JY, Cao S, Wang Y. Failure of Placebo Analgesia Model in Rats with Inflammatory Pain. Neurosci Bull 2019; 36:121-133. [PMID: 31435837 DOI: 10.1007/s12264-019-00420-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2019] [Accepted: 05/21/2019] [Indexed: 12/15/2022] Open
Abstract
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.
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Affiliation(s)
- Xiang-Sha Yin
- Department of Neurobiology, School of Basic Medical Sciences and Neuroscience Research Institute, Key Laboratory for Neuroscience, Ministry of Education of China, and National Health Commission, State key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing, 100083, China
| | - Jin-Yu Yang
- Department of Neurobiology, School of Basic Medical Sciences and Neuroscience Research Institute, Key Laboratory for Neuroscience, Ministry of Education of China, and National Health Commission, State key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing, 100083, China
| | - Shuai Cao
- Department of Neurobiology, School of Basic Medical Sciences and Neuroscience Research Institute, Key Laboratory for Neuroscience, Ministry of Education of China, and National Health Commission, State key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing, 100083, China
| | - Yun Wang
- Department of Neurobiology, School of Basic Medical Sciences and Neuroscience Research Institute, Key Laboratory for Neuroscience, Ministry of Education of China, and National Health Commission, State key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing, 100083, China.
- PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing, 100871, China.
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Akintola T, Tricou C, Raver C, Castro A, Colloca L, Keller A. In search of a rodent model of placebo analgesia in chronic orofacial neuropathic pain. NEUROBIOLOGY OF PAIN (CAMBRIDGE, MASS.) 2019; 6:100033. [PMID: 31223137 PMCID: PMC6565753 DOI: 10.1016/j.ynpai.2019.100033] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 04/18/2019] [Accepted: 05/13/2019] [Indexed: 12/25/2022]
Abstract
All treatments are given in a context, suggesting that conditioning cues may significantly influence therapeutic outcomes. We tested the hypothesis that context affects placebo analgesia in rodents. To produce neuropathic pain in rats, we performed chronic constriction injury of the infraorbital nerve. We then treated the rats daily, over a seven day period, with injections of either fentanyl or saline, with or without associated conditioning cues; a fourth group received no treatment. On the eighth day, we replaced fentanyl with saline to test for conditioned placebo analgesia. We tested the effects of treatment by measuring sensitivity to mechanical stimuli and grimace scale scores. We found no significant differences in either of these outcomes among the four experimental groups. These findings suggest that chronic, neuropathic pain in rats may not be susceptible to placebo analgesia.
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Affiliation(s)
- Titilola Akintola
- Department of Pain and Translational Symptom Science, University of Maryland School of Nursing, Baltimore, MD, USA
- Program in Toxicology, University of Maryland School of Medicine, Baltimore, MD, USA
- Center to Advance Chronic Pain Research, University of Maryland, Baltimore, MD, USA
| | - Christina Tricou
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Charles Raver
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Alberto Castro
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Luana Colloca
- Department of Pain and Translational Symptom Science, University of Maryland School of Nursing, Baltimore, MD, USA
- Center to Advance Chronic Pain Research, University of Maryland, Baltimore, MD, USA
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
- Departments of Anesthesiology and Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Asaf Keller
- Center to Advance Chronic Pain Research, University of Maryland, Baltimore, MD, USA
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
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15
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Abstract
All preclinical procedures for analgesic drug discovery involve two components: 1) a "pain stimulus" (the principal independent variable), which is delivered to an experimental subject with the intention of producing a pain state; and 2) a "pain behavior" (the principal dependent variable), which is measured as evidence of that pain state. Candidate analgesics are then evaluated for their effectiveness to reduce the pain behavior, and results are used to prioritize drugs for advancement to clinical testing. This review describes a taxonomy of preclinical procedures organized into an "antinociception matrix" by reference to their types of pain stimulus (noxious, inflammatory, neuropathic, disease related) and pain behavior (unconditioned, classically conditioned, operant conditioned). Particular emphasis is devoted to pain behaviors and the behavioral principals that govern their expression, pharmacological modulation, and preclinical-to-clinical translation. Strengths and weaknesses are compared and contrasted for procedures using each type of behavioral outcome measure, and the following four recommendations are offered to promote strategic use of these procedures for preclinical-to-clinical analgesic drug testing. First, attend to the degree of homology between preclinical and clinical outcome measures, and use preclinical procedures with behavioral outcome measures homologous to clinically relevant outcomes in humans. Second, use combinations of preclinical procedures with complementary strengths and weaknesses to optimize both sensitivity and selectivity of preclinical testing. Third, take advantage of failed clinical translation to identify drugs that can be back-translated preclinically as active negative controls. Finally, increase precision of procedure labels by indicating both the pain stimulus and the pain behavior in naming preclinical procedures.
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Affiliation(s)
- S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia
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16
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A Context-Based Analgesia Model in Rats: Involvement of Prefrontal Cortex. Neurosci Bull 2018; 34:1047-1057. [PMID: 30178433 PMCID: PMC6246847 DOI: 10.1007/s12264-018-0279-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Accepted: 05/03/2018] [Indexed: 01/01/2023] Open
Abstract
Cognition and pain share common neural substrates and interact reciprocally: chronic pain compromises cognitive performance, whereas cognitive processes modulate pain perception. In the present study, we established a non-drug-dependent rat model of context-based analgesia, where two different contexts (dark and bright) were matched with a high (52°C) or low (48°C) temperature in the hot-plate test during training. Before and after training, we set the temperature to the high level in both contexts. Rats showed longer paw licking latencies in trials with the context originally matched to a low temperature than those to a high temperature, indicating successful establishment of a context-based analgesic effect in rats. This effect was blocked by intraperitoneal injection of naloxone (an opioid receptor antagonist) before the probe. The context-based analgesic effect also disappeared after optogenetic activation or inhibition of the bilateral infralimbic or prelimbic sub-region of the prefrontal cortex. In brief, we established a context-based, non-drug dependent, placebo-like analgesia model in the rat. This model provides a new and useful tool for investigating the cognitive modulation of pain.
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17
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Placebo Analgesia in Rodents: Current and Future Research. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2018; 138:1-15. [PMID: 29681320 DOI: 10.1016/bs.irn.2018.02.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
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.
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18
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Schafer SM, Geuter S, Wager TD. Mechanisms of placebo analgesia: A dual-process model informed by insights from cross-species comparisons. Prog Neurobiol 2018; 160:101-122. [PMID: 29108801 PMCID: PMC5747994 DOI: 10.1016/j.pneurobio.2017.10.008] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 10/24/2017] [Accepted: 10/28/2017] [Indexed: 12/19/2022]
Abstract
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.
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Affiliation(s)
- Scott M Schafer
- Department of Psychology and Neuroscience, University of Colorado, 345 UCB, Boulder, CO 80309, USA
| | - Stephan Geuter
- Department of Psychology and Neuroscience, University of Colorado, 345 UCB, Boulder, CO 80309, USA; Institute of Cognitive Science, University of Colorado Boulder, 344 UCB, Boulder, CO 80309, USA; Department of Biostatistics, Johns Hopkins University, 615 N Wolfe St, Baltimore, MD 21205, USA
| | - Tor D Wager
- Department of Psychology and Neuroscience, University of Colorado, 345 UCB, Boulder, CO 80309, USA; Institute of Cognitive Science, University of Colorado Boulder, 344 UCB, Boulder, CO 80309, USA.
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19
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Abstract
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.
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Abstract
This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY 11367, United States.
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21
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Lee IS, Lee B, Park HJ, Olausson H, Enck P, Chae Y. A new animal model of placebo analgesia: involvement of the dopaminergic system in reward learning. Sci Rep 2015; 5:17140. [PMID: 26602173 PMCID: PMC4658539 DOI: 10.1038/srep17140] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 10/26/2015] [Indexed: 11/09/2022] Open
Abstract
We suggest a new placebo analgesia animal model and investigated the role of the dopamine and opioid systems in placebo analgesia. Before and after the conditioning, we conducted a conditioned place preference (CPP) test to measure preferences for the cues (Rooms 1 and 2), and a hot plate test (HPT) to measure the pain responses to high level-pain after the cues. In addition, we quantified the expression of tyrosine hydroxylase (TH) in the ventral tegmental area (VTA) and c-Fos in the anterior cingulate cortex (ACC) as a response to reward learning and pain response. We found an enhanced preference for the low level-pain paired cue and enhanced TH expression in the VTA of the Placebo and Placebo + Naloxone groups. Haloperidol, a dopamine antagonist, blocked these effects in the Placebo + Haloperidol group. An increased pain threshold to high-heat pain and reduced c-Fos expression in the ACC were observed in the Placebo group only. Haloperidol blocked the place preference effect, and naloxone and haloperidol blocked the placebo analgesia. Cue preference is mediated by reward learning via the dopamine system, whereas the expression of placebo analgesia is mediated by the dopamine and opioid systems.
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Affiliation(s)
- In-Seon Lee
- Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea.,Department of Internal Medicine: Psychosomatic Medicine and Psychotherapy, University of Tübingen, Tübingen, Germany.,Institute for Medical Psychology, fMEG Center, University of Tübingen, Tübingen, Germany.,IMPRS for Cognitive and Systems Neuroscience, University of Tübingen, Tübingen, Germany
| | - Bombi Lee
- Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea
| | - Hi-Joon Park
- Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea
| | - Håkan Olausson
- Center for Social and Affective Neuroscience, Linköping University
| | - Paul Enck
- Department of Internal Medicine: Psychosomatic Medicine and Psychotherapy, University of Tübingen, Tübingen, Germany
| | - Younbyoung Chae
- Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea
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22
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Jargin SV. Hormesis and homeopathy: The artificial twins. JOURNAL OF COMPLEMENTARY MEDICINE RESEARCH 2014; 4:74-7. [PMID: 26401389 PMCID: PMC4566758 DOI: 10.5455/jice.20140929114417] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Accepted: 09/29/2014] [Indexed: 12/25/2022]
Abstract
Homeopathy claims a curative reaction from small doses of a substance, high doses of which cause symptoms similar to those the patient is suffering from. Hormesis is a concept of biphasic dose-response to different pharmacological and toxicological agents. According to this concept, a small dose of a noxious agent can exert a beneficial action. A hypothesis is defended here that hormesis as a general principle can be assumed only for the factors present in the natural environment thus having induced adaptation of living organisms. Generalizations of the hormesis phenomenon used in support of homeopathy are unfounded. Low-dose impacts may be associated with a higher risk in a state of organ sub-compensation or failure especially in the elderly patients. Practical recommendations should be based neither on the hormesis as a default approach nor on the postulates of homeopathy. All clinically relevant effects, hormetic or not, should be tested by the methods of evidence-based medicine.
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Affiliation(s)
- Sergei V Jargin
- Department of Public Health, Peoples' Friendship University of Russia, Moscow, Russia
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