Morris water maze performance. (A) Latency: in the young groups, the performance was significantly impaired by LPS infusion; performance recovered when insulin was infused with LPS (see text). Surprisingly, the young rats receiving only insulin performed better compared to all other groups. Conversely, in the aged rats, insulin did not improve performance as compared to the controls. (B) Velocity: in the young rats, insulin significantly improved performance versus LPS and LPS/insulin groups (P < 0.05). (C) Distance: the distance to find the platform was significantly smaller in the insulin group (P < 0.05) over the 4 days while it was greater in the LPS group. Insulin/LPS was significant versus LPS (P < 0.05) and versus insulin (P < 0.01). Insulin treatment reduced the distance swam as compared to aCSF (P < 0.05). (D) Probe trial: the performance was impaired by LPS infusion as compared to aCSF and insulin (P < 0.05). (Stars) The aged rats showed no differences, P > 0.05, between aCSF and insulin-infused groups.