Conditioned tolerance to drug-induced (poly I:C) natural killer cell activation: effects of drug-dosage and context-specificity parameters

Conditioned manipulation of natural killer (NK) cells in humans using a discriminative learning protocol

There is growing evidence indicating that the immune function can be modified by classical conditioning techniques. This phenomenon, initially explored in animals, is further documented by studies providing evidence that the human immune response can also be influenced by classical conditioning processes. In the present study, we tested the hypothesis that human immune parameters can be modulated by discriminative learning processes. Using a classical discriminative conditioning design, healthy volunteers were provided with a CS+ (sherbet sweet/white noise), which was repeatedly paired with an injection of epinephrine (unconditioned stimulus, US). After epinephrine injections (0.2 mg subcutaneously), a transient increase of natural killer (NK) cell activity (unconditioned response, UR) could be observed. A second stimulus complex (herbal sweet/auditory stimulus, conditioned stimulus, CS-) remained without reinforcement. After repeated presentation of the stimuli, re-exposure of the CS+ on the test trial 1 resulted in a significantly increased number of NK positive (NK+) cells and in slightly elevated NK cell activity. No alteration of NK cells, however, could be observed after presentation of the CS-. A second re-exposure of the CS+ on test trial 3, again resulted in a marked increase of NK+ cell number as well as in significantly elevated NK cell activity. The data presented here extend previous observations of conditioned alteration of immune responses in humans and indicate that the human organism might be able to react differentially to external stimuli, which have been associated with different immunological consequences.

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.

Conditioned tolerance to the anorectic and corticosterone-elevating effects of nicotine

We have shown that tolerance to the behavioral effects of nicotine is partially dependent on conditioned environmental cues that predict drug delivery. The present research extends this finding to physiological effects of nicotine by assessing both the appetite-suppressing and adrenocortical-activating effects of nicotine, as measured by plasma corticosterone (CORT). In the first study, male rats on a 22-h food deprivation schedule were injected daily with 0.33 or 0.66 mg/kg (free base) of nicotine bitartrate or saline in a distinctive environment and tested for milk intake. Nicotine initially suppressed milk intake and tolerance developed over 10 days. Changing cues associated with drug administration partially reversed tolerance since injection of nicotine in a new environment reduced milk intake of tolerant animals. Similarly, animals who repeatedly received nicotine in one environment exhibited CORT levels lower than rats injected for the first time, and this tolerance also was partially reversed when administration occurred in the new environment. The second experiment indicated that the increased CORT of Experiment 1 was not a stress response associated with injecting animals in a different environment. These results indicate that tolerance to both behavioral and neuroendocrine effects of nicotine is influenced by conditioning.

Conditioned taste aversion but not adrenal activity develops to ICV administration of interleukin-1 in rats

In a previous investigation with mice, the paired presentation of either odor or taste cues with the peripheral (IP) administration of the immunoactive peptide interleukin-1 (IL-1) led to the conditioned enhancement of glucocorticoid production. The present study found that an initial central infusion of IL-1 in the presence of saccharin cues produced a robust taste aversion but not a conditioned elevation of either ACTH or corticosterone production. These results indicate that the glucocorticoid response induced by centrally administered IL-1 in rats is independent of the behaviorally aversive properties of this cytokine which are conditionable. The differential effects of IP versus ICV administration of IL-1 on glucocorticoid conditioning requires a clearer specification of the respective signaling mechanisms and pathways activated by these two routes of administration.

The Pavlovian conditioning of IL-1-induced glucocorticoid secretion

Recombinant IL-1-beta, which is capable of stimulating the pituitary-adrenal axis to secrete corticosterone, was paired with environmental cues in either a taste aversion or odor conditioning procedure. Among mice receiving paired delivery of cues and IL-1, subsequent re-exposure to cues elicited corticosterone production. This response was significantly greater than in animals that were conditioned but not re-exposed to the cues or were exposed to the cues alone. These results indicate that the IL-1 activation of adrenal cortical secretion can be conditioned to environmental stimuli.