Abstract
Recurrent infections are common in older individuals. However, there is a paucity of literature on the effect of recurrent infections on cognitive and other responses. The aim of this pilot study was to establish a model of recurrent infections. We examined the effect of recurrent intraperitoneal (ip) administration of lipopolysaccharide (LPS) on food intake, weight loss, spatial learning, and cytokine levels in aged Brown-Norway male rats. To model a recurrent infection, 300 μg/kg LPS (n=5) or saline (n=4) were administered for two consecutive days during two different weeks separated by twenty-one days A hippocampal-dependent measure of spatial learning, the Morris water maze (MWM), was used to evaluate spatial learning beginning five hours after the first injection and continuing for six days. Spatial learning indices were directional heading error (DHE) and swim time latency. Probe trials were used to assess memory. Plasma cytokine levels were assessed 5 and 24 hours after each LPS injection during week two of injections. The experimental group decreased food intake and lost significantly more weight during week one, but both groups displayed increased DHE. While experimental animals exhibited fewer sickness responses during week two, they exhibited spatial learning deficits. Probe trials showed memory deficits in the experimental group. Interleukin-6 (IL-6) was higher at both time points after the first LPS injection in the experimental group. Recurring LPS exposure in aged rats resulted in cognitive impairment despite decreased sickness responses. These results suggest that older individuals may be at higher risk for cognitive impairment following recurrent infections.