Deterioration of spatial learning performances in lipopolysaccharide-treated mice.

It is well demonstrated that acute or chronic stress leads to reduction of learning ability. Lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, induces profound physiological and behavioral changes, including fever, decrease in food motivation, and decrease in social behavior. These changes might be interpreted as an acute stress reaction to the LPS. In the present study, therefore, we investigated the effects of LPS (400-800 microg/kg, i.p.) on spatial learning performances using C57BL/6J male mice. In the Morris water-maze task, spatial learning performances were examined in six trials of training for two consecutive days. LPS-treated mice took a longer time to reach the hidden platform than control mice (F(1,60)=4.80801, P<0.05 at 600 microg/kg). In addition, injection of LPS decreased the percent of correct choices in the Y-maze test (P<0.05 at 800 microg/kg). LPS, however, did not alter the body weight, grip tone, motor activity or swimming speed. Taken together, these results indicate that LPS treatment specifically impaired spatial learning performances.