Effects of intraperitoneal lipopolysaccharide on Morris maze performance in year-old and 2-month-old female C57BL/6J mice

Several studies have shown that systemic lipopolysaccharide (LPS) or interleukin-1β (IL-1β) may affect performance in various learning tasks, including the Morris water maze. In the current study, female C57BL/6J mice, either 2 months or 1 year of age, were given 5 days of testing followed by 3 days of rest, and then three additional days of testing. Mice either received a single LPS injection on day 1 and saline on days 2-5, LPS injections on days 1-5, or saline injections on days 1-5. Daily LPS administration significantly prolonged latency for the animals to find the platform, and decreased their swimming speed. Year-old mice treated with LPS each day also exhibited significantly higher levels of thigmotaxis in the maze. Despite effects on latency and swim speed, no effect of LPS treatment was observed for distance traveled to the platform or other measures that clearly indicate disruption of learning in the maze. On the other hand, age was a significant factor affecting both latency and distance, with older animals swimming greater distances to find the platform. Additionally, older animals were more adversely affected by daily LPS treatment. In this study, although LPS-induced performance impairments in the Morris water maze were noted, particularly in older animals, these effects were not clearly indicative of learning impairment per se.