Lipopolysaccharide (LPS), a bacterial endotoxin which has potent immune activating properties, has been widely used to study the effects of neuroinflammation in animal models. Previous studies have demonstrated that LPS increases the stress response, reduces operant responding, and causes anhedonia and anorexia in rats. Most of these studies have demonstrated the behavioural effects of LPS through decreases in palatable solution consumption or self-administration of pleasurable electrical brain stimulation (EBS), however a more detailed study exploring the differences between appetitive and consummatory behaviours is needed to truly understand the impact of neuroinflammation on food-motivated behaviour. The current study injected 23 male Long Evans rats with either LPS (200 μg/kg; n = 8), scopolamine hydrobromide (SH; 1 mg/kg; n = 7) or a saline control (0.9% saline; n = 8), and assessed bar pressing performance under an FR-1 schedule in a Skinner box. Measures on latency time to begin bar pressing (LT), rate of responding (RR), horizontal movements (HM), and vertical movements (VM) were collected during a 14 min test day session, incremented in 2 min time blocks. Additionally, the number of total bar presses (TBP) was recorded during baseline and testing sessions. The study’s hypothesis that LPS-injected rats would display impaired response to positive reinforcements in the Skinner box was supported; LPS rats underperformed the saline control in all bar pressing measures, including LT, RR, and TBP. However, decreases in LPS rats’ HM and VM suggest that reduction in bar pressing is not solely due to reduced motivation. Future research should further examine the mechanism of LPS effects on appetitive behaviour, and attempt to isolate deficits in locomotor behaviour from reduced food intake.
Ghahari, Daamoon, "The Effects of Lipopolysaccharide on Positive Reinforcement in Rats" (2018). 2018 Undergraduate Awards. 15.