Reward and immunocompetence

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The immunomodulatory effects of rewarding brain stimulation have important functional implications applicable to several central conditions including depression and other stress-related disorders. For example, it has recently been shown that brain stimulation applied to certain structures reduces the depressive symptoms in humans who do not respond to traditional forms of treatment. Understanding the fundamental nature of the relationship between reward and immunological processes is basic to the development of such novel therapies. Protective effects have also been observed as a consequence of environmental enrichment, but there is little data related to its immunological and endocrine influences. In our studies, the expression of sickness behaviours as a consequence of endotoxin challenge differs according to group designation in that animals receiving rewarding brain stimulation display no illness behaviours, roughly half of the animals in the environmental enrichment condition display illness behaviours, and all animals in the control group display illness behaviours. Unlike brain stimulation reward, in which thresholds indicate the rewarding value of the stimulation, there is no index of enrichment to evaluate individual animal responses to their environment. For animals in subordinate positions, for example, the group experience may be less satisfying than for animals in more dominant positions, and affect immunocompetence. The long-term goals of this proposal are to include variables such as age, genetic, and sex differences to determine the contribution of these factors to immunocompetency. Most studies using animal models do not stratify by sex, although it is well-known that there are sex differences in adaptive and innate immunity. Given our general interest in examining the influence of the unique immunological and endocrine profiles associated with females, our studies will be expanded to include both female and male groups.