Activation of the immune system results in release of cytokines that affect memory retrieval and induces a general “sickness behavior” as depicted by decreased appetite, locomotor activity, and motivation to exert effort. Lipopolysaccharide (LPS) delivery has been commonly used to study effects of immune system activation in rats using study paradigms that assess changes in motivational behavior. Food-motivated behaviors are driven by positive reinforcement tasks, which rely on adequate memory retrieval to acquire the sought award. Previous studies determined that LPS has a negative impact on food-motivated behavior as depicted by decreased bar pressing frequency, a quantifiable parameter for operationally defining positive reinforcement. However, previous studies did not consider the role of LPS on locomotor activity on the portrayed decreased bar pressing frequency. Therefore, this study will evaluate the role of LPS administration and dose on positive reinforcement retention (through bar pressing for food release) in rats compared to NaCl treated control rats, and whether LPS has an effect on locomotor activity. It was hypothesized that an immune response via LPS delivery will affect memory retrieval in rats in the form of positive reinforcement tasks (lower bar-pressing frequencies), decreased locomotor activity via lower vertical and horizontal movements when compared to control rats. It was found that LPS-treated rats exhibit decreased locomotor activity, and bar pressing frequency compared to control rats, indicating that the decreased desire to exert effort may explain why LPS negatively impacts positive reinforcement retention.
Kadem, M., & Cross-Mellor, S. (2016). Positive Reinforcement as a Function of Lipopolysaccharide Administration. Western Undergraduate Psychology Journal, 4 (1). Retrieved from https://ir.lib.uwo.ca/wupj/vol4/iss1/13