Conditioned enhancement of skin allografts in mice

Learned Placebo Effects in the Immune System

Associative learning processes are one of the major neuropsychological mechanisms steering the placebo response in different physiological systems and end organ functions. Learned placebo effects on immune functions are based on the bidirectional communication between the central nervous system (CNS) and the peripheral immune system. Based on this “hardware,” experimental evidence in animals and humans showed that humoral and cellular immune functions can be affected by behavioral conditioning processes. We will first highlight and summarize data documenting the variety of experimental approaches conditioning protocols employed, affecting different immunological functions by associative learning. Taking a well-established paradigm employing a conditioned taste aversion model in rats with the immunosuppressive drug cyclosporine A (CsA) as an unconditioned stimulus (US) as an example, we will then summarize the efferent and afferent communication pathways as well as central processes activated during a learned immunosuppression. In addition, the potential clinical relevance of learned placebo effects on the outcome of immune-related diseases has been demonstrated in a number of different clinical conditions in rodents. More importantly, the learned immunosuppression is not restricted to experimental animals but can be also induced in humans. These data so far show that (i) behavioral conditioned immunosuppression is not limited to a single event but can be reproduced over time, (ii) immunosuppression cannot be induced by mere expectation, (iii) psychological and biological variables can be identified as predictors for this learned immunosuppression. Together with experimental approaches employing a placebo-controlled dose reduction these data provide a basis for new therapeutic approaches to the treatment of diseases where a suppression of immune functions is required via modulation of nervous system-immune system communication by learned placebo effects.

Sex and gender in adverse drug events, addiction, and placebo

Sex-gender-based differences in response to pharmaceutical treatments are still under evaluation but evidence already exists regarding the impact of sex-gender-related differences on drug safety profile, drug abuse/addiction, and placebo effects. For a number of drugs it is well recognized that a sex-gender dimorphic profile in terms of drug adverse effects exists and appears to be more frequent and severe in women than in men. However, it is not well known whether this is due to pharmacodynamic or pharmacokinetic differences. Indeed the optimization of therapy requires that attention is paid to single sex-gender. Numerous pharmacokinetic, pharmacodynamic, and sociocultural differences between women and men in drug abuse have been described. Here we focus on sex-gender differences in alcoholism and nicotine addiction. The relevance of sex and gender differences in addiction appear to be relevant. Specific programs aimed to address addicted women's specific needs (child care, pregnancy, housing, and violence and others) are recommended. Finally, this article discusses the possible effect of sex-gender on placebo response in the light of the more significant recent literature evidencing that studies are urgently required in order to better understand the role of sex-gender on placebo mechanism and its impact on randomized clinical trials outcomes.

Behavioural conditioning as the mediator of placebo responses in the immune system

Current placebo research postulates that conditioning processes are one of the major mechanisms of the placebo response. Behaviourally conditioned changes in peripheral immune functions have been demonstrated in experimental animals, healthy subjects and patients. The physiological mechanisms responsible for this 'learned immune response' are not yet fully understood, but some relevant afferent and efferent pathways in the communication between the brain and the peripheral immune system have been identified. In addition, possible benefits and applicability in clinical settings have been demonstrated where behaviourally conditioned immunosuppression attenuated the exacerbation of autoimmune diseases, prolonged allograft survival and affected allergic responses. Here, we summarize data describing the mechanisms and the potential clinical benefit of behaviourally conditioned immune functions, with particular focus on learned placebo effects on allergic reactions.

Conditioned pharmacotherapeutic effects: a preliminary study

OBJECTIVE

To test the hypothesize that psoriasis patients treated under a partial schedule of pharmacologic (corticosteroid) reinforcement would show less severe symptoms and relapse than those given the same amount of drug under standard conditions. Behavioral conditioning as an inherent component of many pharmacotherapeutic protocols has never been examined.

METHODS

A double-blind, simple randomization intervention was conducted with 46 patients from California and New York. Initially, lesions were treated with 0.1% acetonide triamcinolone under standard treatment conditions. Thereafter, a Standard Therapy group continued on continuous reinforcement (active drug every treatment) with 100% of the initial dose; Partial Reinforcement patients received a full dose 25% to 50% of the time and placebo medication other times; Dose Control patients received continuous reinforcement with 25% to 50% of the initial dose.

RESULTS

Severity of disease scores in California neither supported nor refuted the hypothesis. In New York, where there was no difference between Partial Reinforcement and Dose Control groups at baseline, partial reinforcement effected a greater reduction in lesion severity than Dose Control conditions and did not differ from Standard Therapy patients receiving two to four times more drug. For the entire population, the frequency of relapse under partial reinforcement (26.7%) was lower than in Dose Control patients (61.5%) and did not differ from full-dose treatment (22.2%).

CONCLUSIONS

A partial schedule of pharmacotherapeutic reinforcement could maintain psoriasis patients with a cumulative amount of corticosteroid that was relatively ineffective when administered under standard treatment conditions. Conceivably, corticosteroid administration only one quarter or half as frequently as currently prescribed is sufficient to treat psoriasis. We posit, however, that these preliminary observations implicate conditioning processes in-and for the design of-regimens of pharmacotherapy.

Behavioral conditioning with interferon beta-1a in humans

Behavioral conditioning is one of the most impressive demonstrations of brain-immune system interaction. Numerous animal studies have demonstrated behavioral conditioned effects on immune functions, however, human studies are rare. We investigated whether it is possible to behaviorally condition the acute response to interferon (IFN)beta-1a. In a double-blind placebo-controlled study, 30 healthy subjects received a single injection of IFN(beta)-1a (6MIU of REBIF, Serono International) (unconditioned stimulus, UCS) together with a novel drink (conditioned stimulus, CS). Blood was drawn at baseline, 4, 8, and 24 h after drug administration. Within the first 8 h peripheral granulocytes significantly increased, while monocytes, lymphocytes, T-, B- and natural killer (NK) cell numbers were significantly reduced. In parallel, body temperature, heart rate, norepinephrine and interleukin (IL)-6 plasma levels were heightened within 8 h after injection. 8 days later, all previously IFN(beta)-treated subjects received a subcutaneous placebo (NaCl) injection, but only 15 subjects were re-exposed to the CS (experimental group), while a control group (N=15) drank water and an additional group of subjects (n=8) remained untreated (untreated group). Blood sampling was performed at baseline and at 4, 8, and 24 h. Re-exposition to the CS did not elicit conditioned responses in the experimental group. Moreover, no differences were observed between groups. These data provide negative findings regarding behavioral conditioning of cytokine effects in humans employing a one-trial learning paradigm.

Noradrenergic responses of peripheral organs to cyclophosphamide in mice

To determine if the chemotherapeutic drug cyclophosphamide influences the activity of the sympathetic nervous system, the effects of cyclophosphamide on norepinephrine concentration in the heart, adrenal gland, spleen, and thymus gland were evaluated. Male BALB/cByJ mice were administered a single injection of cyclophosphamide (15, 50, or 100 mg/kg, i.p) or saline-vehicle. Organs were collected 72 or 120 h after injection and norepinephrine concentrations were determined by high pressure liquid chromatography with electrochemical detection. Cyclophosphamide reduced spleen, thymus gland, and heart mass while also elevating spleen and thymus gland norepinephrine concentrations (both pmoles/mg tissue and pmoles/mg protein) in a dose- and time-dependent manner. Norepinephrine concentrations in heart and adrenal gland were not altered by cyclophosphamide at any drug dose or time point. Dose- and time-dependent cyclophosphamide-mediated changes in peripheral norepinephrine levels in the spleen and thymus gland are interesting because subjects administered cyclophosphamide may be more susceptible to opportunistic infections, not only because the drug is antineoplastic, but also because the drug alters nervous system-immune system communication and the neurochemical milieu in which surviving cells interact.

Conditioned immunomodulation: research needs and directions

Considering the brief time that psychoneuroimmunology has existed as a bona fide field of research, a great deal of data has been collected in support of the proposition that homeostatic mechanisms are the product of an integrated system of defenses of which the immune system is a critical component. It is now clear that immune function is influenced by autonomic nervous systems activity and by the release of neuroendocrine substances from the pituitary. Conversely, cytokines and hormones released by an activated immune system influence neural and endocrine processes. Regulatory peptides and receptors, once confined to the brain, are expressed by both the nervous and immune systems enabling each system to monitor and modulate the activities of the other. It is hardly surprising, then, that immunologic reactivity can be influenced by stressful life experiences or by Pavlovian conditioning.

One-trial conditioning of the antibody response to hen egg lysozyme in rats

In Wistar rats, reexposure to a novel conditioned stimulus (CS) previously paired with a protein antigen, hen egg lysozyme (HEL) on a single conditioning trial increased anti-HEL IgG levels relative to conditioned rats that were not reexposed to the CS, conditioned rats that were preexposed to the CS, and nonconditioned rats. These results confirm previous findings that a single exposure to a CS associated with immunization is sufficient to elicit an antibody response upon subsequent reexposure to the CS in the absence of exogenous antigen.

On the development of psychoneuroimmunology

Psychoneuroimmunology, the study of interactions among behavioral, neural and endocrine, and immune processes, coalesced as an interdisciplinary field of study in the late 1970s. Some of the early research that was critical in establishing neuroanatomical, neurochemical and neuroendocrine pathways and functional relationships between the brain and the immune system is outlined here. These and subsequent studies have led to the general acknowledgment that the nervous and immune systems are components of an integrated system of adaptive processes, and that immunoregulatory processes can no longer be studied as the independent activity of an autonomous immune system. This paradigm shift in the study of immunoregulatory processes and the elaboration of the mechanisms underlying behaviorally induced alterations of immune function promise a better understanding and a new appreciation of the multi-determined etiology of pathophysiological states.

Behaviorally conditioned immunosuppression using cyclosporine A: central nervous system reduces IL-2 production via splenic innervation

Bi-directional interactions between the central nervous system (CNS) and immune system are demonstrated by the modification of immune function using behavioral conditioning. However, the mechanisms by which the CNS achieves conditioned immunomodulation are still in question. Here, we report that the immunosuppressive effects of cyclosporine A (CsA) can be behaviorally conditioned in rats using saccharin as a gustatory conditioned stimulus. The conditioned effects were compared to control groups that received CsA paired with water (sham-conditioned), CsA injection on test days (CsA-treated), and unhandled rats (untreated). In conditioned animals, the mitogen-induced lymphocyte proliferation in the spleen is significantly suppressed, and the survival time of heterotopic heart allografts prolonged. These effects are paralleled by conditioned inhibition of IL-2 and IFN-gamma synthesis by splenocytes. Furthermore, the CNS-induced immunosuppression is mediated neuronally and not via the blood, since the conditioned reduction of proliferation and cytokine production is completely abrogated after surgical denervation of the spleen. Thus, during conditioning, the CNS learns to reinstate at demand a CsA-like immunosuppression via splenic innervation. This might be used as a supportive therapy for controlling immune functions.

Psychoneuroimmunology: animal models of disease

OBJECTIVE

Psychoneuroimmunology, which investigates the bidirectional communication between the central nervous system and the immune system, has been greatly advanced by the use of animal models. The objective of this paper is to describe animal models of disease that can or might be utilized to elucidate neural-immune interactions that alter pathogenesis.

METHODS

This paper reviews animal studies that have demonstrated a link among the brain, behavior, immunity, and disease, highlighting models in which the potential contribution of CNS-immune interactions has not yet been explored.

RESULTS

Animal studies allow for careful control of environmental stimuli, genetic background, and immunological challenge. As such, they are an important component of psychoneuroimmunology research. Models in which one might study the role of psychosocial factors in immunologically mediated disease processes, as in the case of other pathophysiologic processes, profit from an ability to manipulate both stressful events and the magnitude of the challenge to the immune system.

CONCLUSIONS

Animal studies in psychoneuroimmunology highlight the complexity of the interactions among behavior, the brain, the immune system, and pathogen. The genetic background of the animal (both in terms of central nervous and immune system responses), its previous history, the nature of the stressor, the nature of the pathogen and the type of immune response generated are some of the interacting factors that determine the magnitude and direction of stress-induced changes in disease outcome.

Conditioning of the allogeneic cytotoxic lymphocyte response

Allogeneic cytotoxic T-lymphocyte (CTL) response can be obtained following immunization of BALB/c mice with C57BL/6 spleen cells. We investigated the possibility of behaviorally conditioning this response by associating the C57BL/6 spleen cell immunization [unconditioned stimulus (US)] with camphor odor [conditioned stimulus (CS)]. We reported the possible mechanisms involved in the conditioning of natural killer cell activity. Similar approaches were used to investigate the mechanisms that participate in the conditioned CTL activity. The first mechanism of investigation utilized opioid receptor blockers naltrexone and quaternary naltrexone. Naltrexone, which blocks both the central and peripheral opioid receptors, blocked the recall of the conditioned response, whereas quaternary naltrexone, which does not penetrate the blood-brain barrier, was unable to block the conditioned response, demonstrating that centrally located opioid receptors play a role in the recall of the conditioned response. The studies are of interest because they indicate that resistance or susceptibility to various diseases such as cancer, autoimmunity, and infectious diseases might be influenced by the regulatory network of the CNS.

Conditioned immunopharmacologic effects on cell-mediated immunity

One of the several lines of evidence documenting a relationship between the brain and the immune system is the research on behaviorally induced alterations in immune reactivity. The present review concentrates on the use of immunopharmacologic agents, stress, and antigenic stimuli as unconditioned stimuli (UCSs) in the classically conditioned suppression and enhancement of cell-mediated immune reactions including host-vs-graft and graft-vs-host reactions and delayed type hypersensitivity.

Behavioral conditioning prolongs heart allograft survival in rats

Conditioned immunosuppression using a taste aversion paradigm has been demonstrated in a number of laboratory models but few reports have demonstrated changes in immunity sufficient to be of clinical relevance. The experiments reported here demonstrate that the survival of heart allografts in rats can be prolonged by behaviorally conditioned immunosuppression using cyclosporin A (CsA) as an unconditioned stimulus in taste aversion conditioning. Conditioned animals received saccharin as the conditioned stimulus paired with an injection of CsA at 10 and 6 days prior to transplantation. They were reexposed to saccharin alone 1 day prior to and 3 days after transplantation. On these occasions the conditioned group displayed taste aversion behavior when offered saccharin and a significant prolongation of heart graft survival was observed compared to the conditioned and nonconditioned control groups. These experiments suggest that behaviorally conditioned immunosuppression may have important clinical implications as an adjunct to drug treatments in transplantation medicine.