Conditioned enhancement of natural killer cell activity, but not interferon, with camphor or saccharin-LiCl conditioned stimulus

Pavlovian Conditioning of Immunological and Neuroendocrine Functions

The phenomenon of behaviorally conditioned immunological and neuroendocrine functions has been investigated for the past 100 yr. The observation that associative learning processes can modify peripheral immune functions was first reported and investigated by Ivan Petrovic Pavlov and his co-workers. Their work later fell into oblivion, also because so little was known about the immune system’s function and even less about the underlying mechanisms of how learning, a central nervous system activity, could affect peripheral immune responses. With the employment of a taste-avoidance paradigm in rats, this phenomenon was rediscovered 45 yr ago as one of the most fascinating examples of the reciprocal functional interaction between behavior, the brain, and peripheral immune functions, and it established psychoneuroimmunology as a new research field. Relying on growing knowledge about efferent and afferent communication pathways between the brain, neuroendocrine system, primary and secondary immune organs, and immunocompetent cells, experimental animal studies demonstrate that cellular and humoral immune and neuroendocrine functions can be modulated via associative learning protocols. These (from the classical perspective) learned immune responses are clinically relevant, since they affect the development and progression of immune-related diseases and, more importantly, are also inducible in humans. The increased knowledge about the neuropsychological machinery steering learning and memory processes together with recent insight into the mechanisms mediating placebo responses provide fascinating perspectives to exploit these learned immune and neuroendocrine responses as supportive therapies, the aim being to reduce the amount of medication required, diminishing unwanted drug side effects while maximizing the therapeutic effect for the patient’s benefit.

Review of lithium effects on immune cells

One of the remarkable discoveries in the field of psychopharmacology from late 1940s is Lithium (Li) that reminds of old but still gold. It continues to be a distinctive mood stabilizer that matches various standards recommended for mood stabilizers. Apart from this Li is also known to affect immune cell functions. Lithium response and regulations of different immune cells in bipolar patients, related immune disorders are not well defined. Here, we provide an overview of literature with regard to Li's effects on different immune cells. However, the use of Li is currently limited to bipolar disorders and there is no empirical evidence for immune cell disorders. The objective of this article is to provide the evaluations of Li responses towards the different immune cells based on the existing studies. Further, more studies are needed to understand the mechanistic basis and heterogeneous responses of Li's effect in bipolar, also unravel relative immune disorders.

Chemical composition and free radical-scavenging, anticancer and anti-inflammatory activities of the essential oil from Ocimum kilimandscharicum

OBJECTIVE

The essential oil from the leaves of Ocimum kilimandscharicum (EOOK), collected in Dourados-MS, was investigated for anticancer, anti-inflammatory and antioxidant activity and chemical composition.

MATERIALS AND METHODS

The essential oil was extracted by hydrodistillation, and the chemical composition was performed by gas chromatography-mass spectrometry. The essential oil was evaluated for free radical-scavenging activity using the DPPH assay and was tested in an anticancer assay against ten human cancer cell lines. The response parameter (GI50) was calculated for the cell lines tested. The anti-inflammatory activity was evaluated using carrageenan-induced pleurisy in mice.

RESULTS

The chemical composition showed 45 components with a predominance of monoterpenes, such as camphor (51.81%), 1,8 cineole (20.13%) and limonene (11.23%). The EOOK exhibited potent free radical-scavenging activity by the DPPH assay with a GI50 of 8.31 μg/ml. The major constituents, pure camphor (IC50=12.56 μg/ml) and mixture of the limonene: 1, 8 cineole (IC50=23.25 μg/ml) displayed a potent activity. The oral administration of EOOK (at 30 and 100 mg kg(-1)), as well as the pure camphor or a mixture of 1,8 cineole with limonene, significantly inhibited the carrageenan (Cg) induced pleurisy, reducing the migration of total leukocytes in mice by 82 ± 4% (30 mg kg(-1) of EOOK), 95 ± 4% (100 mg kg(-1) of EOOK), 83 ± 9% (camphor) and 80 ± 5% (mixture of 1,8 cineole:limonene 1:1). In vitro cytotoxicity screening against a human ovarian cancer cell line displayed high selectivity and potent anticancer activity with GI50=31.90 mg ml(-1). This work describes the anti-inflammatory, anticancer and antioxidant effects of EOOK for the first time.

CONCLUSIONS

The essential oil exhibited marked anti-inflammatory, antioxidant and anticancer effects, an effect that can be attributed the presence of majorital compounds, and the response profiles from chemical composition differed from other oils collected in different locales.

Camphor--a fumigant during the Black Death and a coveted fragrant wood in ancient Egypt and Babylon--a review

The fragrant camphor tree (Cinnamomum camphora) and its products, such as camphor oil, have been coveted since ancient times. Having a rich history of traditional use, it was particularly used as a fumigant during the era of the Black Death and considered as a valuable ingredient in both perfume and embalming fluid. Camphor has been widely used as a fragrance in cosmetics, as a food flavourant, as a common ingredient in household cleaners, as well as in topically applied analgesics and rubefacients for the treatment of minor muscle aches and pains. Camphor, traditionally obtained through the distillation of the wood of the camphor tree, is a major essential oil component of many aromatic plant species, as it is biosynthetically synthesised; it can also be chemically synthesised using mainly turpentine as a starting material. Camphor exhibits a number of biological properties such as insecticidal, antimicrobial, antiviral, anticoccidial, anti-nociceptive, anticancer and antitussive activities, in addition to its use as a skin penetration enhancer. However, camphor is a very toxic substance and numerous cases of camphor poisoning have been documented. This review briefly summarises the uses and synthesis of camphor and discusses the biological properties and toxicity of this valuable molecule.

Lipopolysaccharide and IL-1 alpha activate CNS pathways as measured by NK cell activity

The effect of lipopolysaccharide (LPS) on murine unstimulated and prestimulated natural killer (NK) cells and its ability to serve as an unconditioned stimulus was investigated. LPS injection induced a statistically significant increase in NK cell activity when compared with saline-treated control groups. To demonstrate the existence of communication between the peripheral immune system and the central nervous system (CNS), we used a single-trial conditioning paradigm in which camphor served as the conditioned stimulus (CS) and LPS as the unconditioned stimulus (US). Once a CS/US association is made, exposure of animals to the CS alone results in the conditioned response (i.e., increase in NK cell activity). Using 50 micrograms of LPS as the US produced a low but significant increase in NK cell activity when compared to control groups. However, 10 micrograms of LPS did not show a significant increase in NK cell activity. We also observed that interleukin-1 alpha (IL-1 alpha) injected intracisternally can serve as a US to condition a central neuroendocrine pathway. Because the dose of IL-1 alpha employed was too small to raise NK cell activity in the spleen, the NK cells themselves were formally not subjected to conditioning. These observations suggest that LPS and IL-1 alpha conditions the brain and that NK cell activity can be used as an indicator system to detect neuroendocrine signals arising from the activated pathway(s).

The use of conditioning to probe for CNS pathways that regulate fever and NK cell activity

Immune and central nervous system (CNS) interactions are complicated because afferent signals from the immune system to the CNS in response to antigens or infections may elicit an immediate efferent response to the immune system. This communication loop is required for the homeostatic regulation of the immune system. Conditioning can be used as a tool to take the communication loop apart. In conditioned animals, the conditioned stimulus can be employed later to trigger the site of the association memory located within CNS, and set off the efferent pathway. Conditioning therefore allows one to isolate and identify the potential circuits in the brain that becomes conditioned. We have conditioned a pathway in the brain which can be used to modulate core body temperature (Tc) and natural killer (NK) cell activity. The Tc and NK cell activity are used as readouts to detect the expression of the conditioned response which is taking place in the brain. Since various cytokines (IFN, IL-1 etc) that are produced by antigenic stimulation invariably raise fever, it appears that the immune system could signal the CNS with nonspecific cytokines that activate the hypothalamic-pituitary pathway to modulate core body temperature. These observations infer that the thermoregulatory pathway in the brain becomes conditioned and points to a common pathway of communication in which interferon-beta, prostaglandin E2, CRH and ACTH appear to play a role in modulating both Tc and NK cell activity.

Sodium carbonate prevents NK cell conditioning by interfering with the US signal

The conditioned enhancement of natural killer (NK) cell activity can be blocked by the injection of sodium carbonate solution prior to the association of the camphor odor conditioned stimulus (CS) with the polyinosinic:polycytidylic acid (poly I:C) unconditioned stimulus (US). We have experimentally dissociated the memory which is formed for camphor odor from that developed for the association of camphor with the US. The memory for the odor of camphor can be allowed to develop one day before the administration of the unconditioned stimulus. Sodium carbonate appears to act within the central nervous system to block the association of the unconditioned stimulus with the conditioned stimulus. The data also suggest that in conditioning of NK cell activity, there are two specific sites for memory of the response, one for the conditioned stimulus and the other for the association of the unconditioned stimulus with the conditioned stimulus.

Behaviorally conditioned modulation of natural killer cell activity: enhancement of baseline and activated natural killer cell activity

Natural killer (NK) cells comprise a sub-population of lymphocytes functionally defined by their ability to spontaneously lyse select tumor and virally infected cells. NK cell lytic function is sensitive to modulation by cytokines and neuroendocrine mediators. Behavioral conditioning trains an animal to cognitively associate a novel environmental cue (i.e. odor) with a physiologically active agent (i.e. Polylnosinic:PolyCytidilic acid, Poly I:C). Poly I:C induces interferon production resulting in activation of NK cells and enhanced NK cell lytic activity. Subsequent to behavioral conditioning, independent presentation of the odor should elicit similar responses (enhanced NK cell activity). We have shown that animals pre-exposed to the conditioning apparatus or manual restraint prior to behavioral conditioning demonstrate enhanced baseline NK cell activity or no effects respectively. To assess the influence of NK cell activation in conjunction with behavioral conditioning, we have re-presented the odor to animals with activated or baseline NK activity. Lymphocytes were then incubated for five days with IL-2 and cellular cytotoxic activity re-assessed. Behavioral conditioning significantly enhanced baseline and activated NK cell activity in animals previously exposed to the conditioning apparatus. No differences in lytic activity versus NK sensitive targets were observed following IL-2 activation. In contrast, animals manually restrained prior to conditioning showed no differences in baseline or in vivo activated NK activity, but previously non-activated lymphocytes stimulated with IL-2 demonstrated significantly higher lytic activity in conditioned animals re-presented with the odor. These results demonstrate central nervous system (CNS) modulation of NK cell activity and the presence of an interplay between cytokine activation and responsiveness to CNS immunoregulatory signals.

Behaviorally conditioned modulation of natural killer cell activity: effects of pre-conditioning manual restraint and apparatus exposure

This study investigated behaviorally conditioned modulation of natural killer cell (NK) activity. One and three trial behavioral conditioning training trial designs were examined. In addition, the influence of pre-conditioning exposure to manual restraint and the conditioning apparatus upon behaviorally conditioned natural killer cell responses was assessed. Prior to one trial training, animals were exposed to either the conditioning apparatus, manual restraint, or were undisturbed. The animals were then trained to associate the conditioned stimulus (CS) and the unconditioned stimulus (US), and later re-presented with the CS. Behaviorally conditioned animals demonstrated significantly enhanced NK cell activity, no difference in NK activity, or significantly decreased NK activity, respectively. There was also a significant interaction between the manual restraint and behavioral conditioning interventions. Animals in a three training trial design were either manually restrained daily prior to and during behavioral conditioning or were left undisturbed. In this design behavioral conditioning significantly decreased NK cell activity and manual restraint significantly increased NK cell lytic activity. These data illustrate behaviorally conditioned decreases and increases in NK cell lytic activity dependant upon the experimental design. Behaviorally conditioned NK cell activity is influenced by additional behavioral interventions (i.e. manual restraint and novelty of conditioning environment) inherent within the behavioral conditioning procedures.

The identity of the unconditioned stimulus to the central nervous system is interferon-beta

The specific mechanism of interaction between the central nervous system and immune system was examined using conditioned augmentation of natural killer (NK) cell activity. This study focused on the role of interferon-beta (IFN-beta) as the unconditioned stimulus (US). IFN-beta was found to be the signal responsible for the bidirectional communication which links the central nervous system with the immune system. This was substantiated by injection of small quantities of IFN-beta directly into the cisterna magna, which activated the effector pathway from the central nervous system to the immune system. More importantly, we found that when the conditioned stimulus (CS) was paired with an injection of IFN-beta into the cisterna magna, the conditioned animals were able to raise their natural killer cell activity in response to subsequent exposure to the conditioned stimulus. These studies show the unconditioned response must be the response of the central nervous system (CNS) to the unconditioned stimulus and not the direct effect of the substance injected into the periphery.

Identification of specific pathways of communication between the CNS and NK cell system

The specific signals and pathways utilized by the natural killer (NK) cell system and the central nervous system (CNS) that results in the conditioned response (CR) is not clearly understood. Single trial conditioning of the NK cell activity provides us with a model to probe the mechanisms of communication between two major systems (Immune and CNS) which are involved in the health and disease of the individual. The studies show that the IFN-beta molecules possess the properties attributed to the unconditioned stimulus (US). IFN-beta can penetrate the CNS and evoke the elevation of NK cell activity in the spleen. This unconditioned response (UR) can be linked to a specific conditioned stimulus (CS). Specific odors such as camphor provide a neural pathway for the CS to associate with the US. Evidence is presented that in conditioning there are two locations where memory develops. The CS/US association is made centrally and its memory is stored at a central location, but the memory for the specificity of the odor is presumably stored in the olfactory bulbs. The CS recalls the CR by triggering the olfactory neural pathway which, in turn, signals the hypothalamic-pituitary axis to release mediators that modulate the activity of NK cells in the spleen. These results imply that through conditioning one has direct input into the regulatory hypothalamus that controls the internal environment of the organism and the health and disease of the individual. Consequently, it is not inconceivable that through this approach we might be able to alter the course of a disease process.

Indomethacin and sodium carbonate effects on conditioned fever and NK cell activity

The augmentation of natural killer (NK) cell activity and elevation of body temperature (fever) can both be conditioned using camphor odor as the conditioned stimulus (CS) and poly I:C as the unconditioned stimulus (US). While both responses can be conditioned in parallel fashion as shown previously, our results indicate the conditioned learning of these responses may not follow along a common path. We found that injection of a 1% solution of sodium carbonate was able to consistently block the CS/US learning of the NK cell response but did not block conditioning of the fever response. In contrary fashion, mice treated with indomethacin (which inhibits prostaglandin-induced fever) dissolved in the sodium carbonate solution did not learn in consistent fashion the fever response. However, indomethacin-treated animals were able to recall the NK cell response. These results support the view that although the same mediator, IFN-beta, is responsible for the conditioned learning of the NK cell and fever responses both the learning and recall of the responses are initiated along separate pathways.

The central effect of methionine-enkephalin on NK cell activity

The central effect of opioid peptide on natural killer (NK) cell activity in BALB/c mice was investigated. Injection of methionine-enkephalin (Met-Enk), 0.02 microgram/mouse or 1 microgram/kg, directly into the cisterna magna (CM) of the brain, resulted in a significant enhancement of NK cell activity. This enhancement was blocked by opiate antagonists, naltrexone and quaternary naltrexone. The same dose of Met-Enk had no effect on NK cell activity when given to the mouse intraperitoneally or intravenously. Moreover, des-tyrosine-methionine-enkephalin injected into the CM at 1 microgram/kg, had no effect on NK cell activity. The results indicate that activation of an opioid-mediated pathway in the central nervous system is capable of activating the pathways that stimulate the NK cell response in the periphery.

Acquisition of enhanced natural killer cell activity under anesthesia

An increase in natural killer (NK) cell activity can be conditioned with a one trial learning paradigm to demonstrate the interaction between the central nervous system (CNS) and the immune system. In order to demonstrate learning possibilities during 'non-conscious' state, mice were anesthetized with a ketamin/rompun mixture and underwent one trial learning with odor cue as the conditioned stimulus (CS) preceding the unconditioned stimulus (US). The results indicated that mice that were exposed to camphor odor cue under the influence of anesthesia can associate the signal with the poly I:C unconditioned stimulus and were able to recall the conditioned response upon reexposure to the CS. Secondly, the conditioned association made in a conscious state can be recalled by exposure to the same olfactory odor cue in a 'non-conscious' state. The increase in the conditioned change in NK cell activity of both situations was significantly higher than the control group. The results demonstrate that learning can take place and the learned response can be recalled under the reduced awareness caused by anesthesia. The findings we report are unusual and novel in that they demonstrate that the CNS can learn new associations under conditions where the host is apparently unaware of the signals being linked. Anesthesia combined with the long interstimulus interval indicates that certain neuronal pathways in the CNS are receptive to second signals (elicited by the US) even when the second signal is separated by one day. This means the conditioned learning of a physiological response can take place unconsciously at a separate level and under situations where the host is totally unaware of the events which the brain is processing and linking as incoming information.

A behavioral augmentation of natural immunity: odor specificity supports a Pavlovian conditioning model

BALB/c mice were conditioned by pairing an odor to an injection of poly-inosinic:poly-cytidylic acid (poly I:C), a strong inducer of natural killer (NK) cell activity as the unconditioned stimulus (US). When later reexposed to the odor conditioning stimulus (CS), these mice showed a conditioned augmentation of the NK cell response to a suboptimal dose of 1 microgram poly I:C. The two stimuli used in these studies were camphor (Ca) and citronella oil (Cr) odors, two chemically-related but distinct odor stimuli. The conditioned mice demonstrated the ability to discriminate between Ca and Cr, such that the conditioned response (CR) was only elicited by the odor CS used in the formation of the conditioned association. Exposure of conditioned mice to the non-associated odor stimulus on the test day did not elicit a change in the NK cell response to the suboptimal dose of poly I:C when compared to mice in the US group that had been given the US on day 0 without pairing to either odor stimulus. This specificity of the CR for the odor CS and not the unassociated odor stimulus supports the interpretation that the elevation of NK cell activity in this paradigm is due to Pavlovian conditioning and therefore dependent on central nervous system (CNS) associative processes.

In vivo enhancement of NK cell activity with met-enkephalin and glycyl-glutamine: their possible role in the conditioned response

These studies investigated the effect of met-enkephalin, glycyl-glutamine, and naltrexone on NK cell activity in vivo and in vitro. It was found that both met-enkephalin (which shares the amino-terminal end of beta-endorphin) and glycyl-glutamine (which reflects the carboxyl-terminal end of beta-endorphin) can enhance the NK cell activity of mice prestimulated with a low dose (1 microgram/mouse) of poly I:C. Naltrexone had no effect. In vivo prestimulation of the mice with 1 microgram poly I:C was necessary as mice which were not pretreated with poly I:C did not show enhanced NK cell activity when treated with either met-enkephalin or glycyl-glutamine. In vitro studies however indicate that the drugs when cultured together with the NK cells from mice preactivated with poly I:C did not have a direct stimulatory effect on the NK cells. These studies imply that while beta-endorphin released from the pituitary could be involved in enhancement of activated NK cells in vivo other indirect peripheral pathways might be involved. The results suggest beta-endorphin probably reacts with other accessory type cells which in turn release the mediators which are required for the stimulation of NK cells in vivo.

Effect of reserpine on retention of the conditioned NK cell response

The effect of reserpine and 6-hydroxydopamine on the learned conditioned natural killer (NK) cell response was investigated in mice. Reserpine given at 2.5 mg/kg, 24 hr prior to reexposure to camphor-conditioned stimulus on days 6 and 8 blocked the recall of conditioned NK cell response to a significant extent. In other words, the NK cell activity of conditioned mice, treated with reserpine and reexposed to the conditioned stimulus, was similar to the nonconditioned (NC) group. A conditioned increase in NK cell response was still evident in mice treated with 6-OHDA.

Naltrexone blocks the expression of the conditioned elevation of natural killer cell activity in BALB/c mice

An elevation of natural killer (NK) cell activity was conditioned by the association of a camphor odor conditioning stimulus (CS) with an injection of 20 micrograms polyinosinic:poly-cytidylic acid (poly I:C), the unconditioned stimulus (US). Poly I:C elicits the production and secretion of interferon (IFN), which induces an increase in NK cell activity. Reexposure to the CS occurred on Days 3 and 5 after the association trial on Day 0. Immediately following the CS exposure on Day 5, 1 microgram poly I:C was administered to all animals. This procedure resulted in an increased NK cell activity in the conditioned (CND), but not the nonconditioned (NC), mice. In this study we have shown that the expression of the conditioned response was blocked by an injection of naltrexone (NTX) at 10 mg/kg ip when given immediately prior to the two test CS odor exposures. Peripheral treatment (ip) with a quaternary form of naltrexone (QNTX), which is a less potent opiate antagonist, at the same dose and at the same time relative to the CS odor reexposure did not block the conditioned response. The formation of the conditioned association did not appear to be disrupted by NTX at the 10 mg/kg dose when given immediately prior to the trial odor exposure on Day 0. No modulation of NK cell activity was observed in any of the control groups treated with naltrexone or the quaternary analog. Because of the inability of the QNTX to block the conditioned response, we hypothesize that the opiate receptors involved in the conditioned response and blocked by NTX were within the central nervous system (CNS). Whether this response is peripherally or centrally mediated, we have shown that opiate receptors represent part of the mechanism which mediates the conditioned augmentation of NK cell activity.