Lipopolysaccharide inhibits the simultaneous establishment of LiCl-induced anticipatory nausea and intravascularly conditioned taste avoidance in the rat

This study examined the effects of the bacterial endotoxin, lipopolysaccharide (LPS), on the establishment of anticipatory nausea and conditioned taste avoidance in a simultaneous conditioning paradigm using an intravascular/intraperitoneal saccharin taste. 83 naïve adult male Long-Evans rats were injected (intraperitoneal) with either 200 μg/kg LPS or 0.9% saline (NaCl), 90 min prior to ip treatment with either 64 mg/kg LiCl, 64 mg/kg LiCl + 2.0% saccharin, 0.9% NaCl, or 0.9% NaCl + 2.0% saccharin, and immediately placed into a distinctive context for 30 min (repeated over 4 conditioning days, spaced 72 h apart). 72 h following the final conditioning day, each animal was re-exposed to the context on a drug-free test day where orofacial responding was recorded. The next day, animals received a 24 h 2-bottle preference test with a choice between water and a palatable 0.2% saccharin solution. Results showed that LPS exposure, prior to LiCl or LiCl + Saccharin treatment, inhibited the establishment of anticipatory nausea, as evidenced by significantly lower conditioned gaping frequencies relative to animals pre-treated with NaCl followed by LiCl or LiCl + Saccharin. LPS pre-treatment also inhibited the formation of LiCl-induced taste avoidance, as evidence by significantly higher saccharin preferences in Group LPS–LiCl + Saccharin relative to Group NaCl–LiCl + Saccharin. The results of the current study provide additional evidence for the deleterious effects of LPS on learning and memory in aversive conditioning.

► Immune system stimulation impairs anticipatory nausea and conditioned taste avoidance.
► LPS inhibits LiCl-induced conditioned gaping.
► LPS inhibits LiCl-induced intravascularly conditioned taste avoidance.
► LPS produced robust initial weight loss relative to NaCl pre-treated animals.
► LPS disrupts learning and memory in a simultaneous aversive conditioning paradigm.