Effects Of Intraperitoneal Lipopolysaccharide On Memory Function In Adult And Aged Rats

Objective: To explore the effects of intraperitoneal lipopolysaccharide (LPS) on memory function in adult and aged rats.Methods: Adult and aged male rats were randomly assigned to four groups: adult rats and saline group (group C); adult rats and LPS group (group L); aged rats and saline group (group A); aged rats and LPS group (group A+L). The rats were injected intraperitoneally with LPS (250μg/kg) or sterile saline immediately after the rats were trained to acquire passive avoidance. The latency period of entering the dark compartment was recorded as memory performance 24 h after train. The hippocampus was removed for determination of IL-1βprotein expression using ELISA and analysis of caspase-1 activity. Furthermore, the expression of IL-18 mRNA and IL-18 protein were analyzed by RT-PCR and ELISA in aged hippocampus.Results: The latency period in group A+L was significantly shorter than that in group A (P<0.01) and there was no significant difference between group L and C (P>0.05). The caspase-1 activity in group A+L was significantly higher than that in group L (P<0.05). A two-way ANOVA of memory test revealed a significant interaction between age and LPS (P<0.01). Post-hoc analysis indicated IL-1βlevels in group L were significantly higher than that in group C (P<0.05). The expression of IL-1βin group A+L was significantly enhanced compared to that in group L and A (P<0.01). IL-18 mRNA and IL-18 protein levels in group A+L were significantly higher than that in group A (P<0.01).Conclusion: Intraperitoneal lipopolysaccharide impairs memory function not in adult but in aged rats, probably because aging enhances LPS-induced increase in hippocampal IL-1βprotein expression. The role of IL-18 in memory disorders induced by intraperitoneal lipopolysaccharide in aged rats needs further study.