Immune, hormonal and neural mechanisms of ingestive behavior

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All organisms need to solve the problem of obtaining nutrients (protein, carbohydrates, fats, and other essential substances) from their environment without eating significant amounts of toxins which are often found in various foods. Many plants (and some animals) protect themselves by producing toxins so that they are less likely to be eaten. Mammals, including humans, have evolved a number of ways (poison avoidance system) to reduce exposure to toxins in the foods eaten. Toxins can be avoided on the basis of taste, post-ingestional effects, and learning. We have been using behavioral responses produced when tastants are infused into the mouth (taste reactivity test), to study this poison avoidance system. We can introduce low levels of a toxin (LiCl) into a food (sucrose solution) or inject the toxin after the animal has eaten a food, and examine changes in the rat's behavior as a result of post-ingestive effects of the toxin. Rats can also be made sick by treating them with a bacteria derived compound (lipopolysaccharide) which produces a syndrome of sickness behaviors (reduced interest in eating, drinking, and increased lethargy). We are studying the effects of bacterial infection on the sensitivity of the poison avoidance system. We have some evidence to suggest that bacterial infection sensitizes the toxin avoidance system, or can block food related learning. We are interested in the brain system(s) that control these processes. We are also interested in the effects of exposure to stress on this process of activating and sensitizing the toxin avoidance system. Many patients that are sick because of immune system activation, such as during bacterial or viral infections, are exposed to toxic chemotherapy treatments for other problems (cancer, AIDS) and their eating behaviors may be compromised leading to lower success for the treatments. This research should provide important information to help with this problem.