Anorexic and Forgetting Effects of Lipopolysaccharide on Positive Reinforcement in Rats

It is widely demonstrated that lipopolysaccharide (LPS), a gram-negative bacteria derived endotoxin, induces symptoms that present similar to a stress response, commonly referred to as ‘sickness behaviours’. The purpose of this study was to examine the effects of LPS on learnt food motivated behaviours in rats by analyzing bar pressing behaviours in a Skinner box under an FR-1 schedule. 23 male Long Evans rats were injected with either 200 μg/kg LPS (n = 8), 1 mg/kg of scopolamine hydrobromide (a known memory blocker; n = 7), or a saline control injection (n = 8). Prior to injection, rats were taught through shaping techniques that bar pressing resulted in reward in the form of food pellets. Baseline and test day measures of bar pressing were taken and compared. Bar pressing behaviours analyzed included locomotor activity, number of bar presses, rate of responding, and latency to first response during a 14 min session (2 min time bins). ANOVA was conducted to examine the trends. As expected, LPS rats performed significantly worse on learnt food motivated tasks than control rats, with decreased locomotion, decreased bar pressing, a slower rate of responding, and an increased latency to first response. These findings suggest LPS disrupts learnt food motivated behaviours. Implications lie in potential cytokine monitoring of the anti-psychotic drug induced weight gain seen in the treatment of schizophrenia. Future studies might look into distinguishing LPS induced memory impairment from the anorexic effects of LPS