Effects of carvacrol on spatial learning performances, hippocampal interleukin-1ß level and oxidative stress markers in lipopolysaccharide-treated rats

Introduction: Peripheral administration of lipopolysaccharide (LPS), can cause production of cytokines in the brain and subsequently impair learning and memory function. Carvacrol is a phenolic monoterpene that is found in the essential oils of the Lamiaceae family. Anti-inflammatory and antioxidant activities of carvacrol have been demonstrated in previous studies. The aim of the current study was to evaluate the effects of carvacrol on spatial learning performances in LPS-treated rats. Methods: Male Wistar rats were pretreated with carvacrol at doses of 10, 25 and 50mg/kg for a week. Then, the animals received LPS injection (1mg/kg, ip) and treatments continued for 3 more weeks. Spatial learning performances were assessed in rats by the Morris water maze from post-injection days 18 to 21. Biochemical assays (interleukine-1β, lipid peroxidation and total thiol levels) were performed in the hippocampus and cerebral cortex at the end of the experiment. Results: LPS-treated rats displayed higher escape latency and longer traveled distance as compared to control rats. In addition, chronic treatment of LPS-treated rats with carvacrol at a dose of 25mg/kg significantly decreased escape latency and traveled distance as compared to untreated-LPS rats. Biochemical assessments showed no significant difference in inflammatory and oxidative stress markers levels among the groups. Conclusion: Our findings demonstrated that chronic treatment with carvacrol improves spatial learning performances in LPS-treated rats. This might be due to antioxidant, anti-inflammatory and anticholinesterase activities of carvacrol in early LPS challenge.