Fig. 3. Intermittent LPS Exposure During Aging Subtly Impairs Cognitive Function.

A. Open Field Locomotor Activity. There were no group differences in (A_i) vertical movement (rearing behavior) nor (A_ii) horizontal movement in the arena. B. Inhibitory (Passive) Avoidance Learning and Retention. Though neither group differed in their latency to enter the darkened compartment on the learning trial prior to shock pairing (p > 0.20), LPS-treated mice showed a trend towards impaired learning on the immediate retention trial (~20 min delay) relative to Vehicle-treated mice; removal of a significant outlier revealed a significant learning impairment of LPS. Vehicle-treated, but not LPS-treated, mice displayed longer term retention of the shock-location pairing. C. Hot Plate Nociception. Groups did not differ on either (C_i) latency to display nociceptive behaviors nor (C_ii) total nociceptive behaviors displayed on the hot plate test. D. Visible Platform Performance. There were no group differences in (D_i) latency to platform, nor (D_ii) swim speed. E. Morris Water Maze Spatial Reference Learning and Memory. Overall learning curves did not differ between the groups (E_i), and there was a lack of group differences in the extent to which mice explored the previously platformed quadrant on the Probe trial (E_iii), indicating that all mice similarly acquired the spatial location of, and utilized a spatial strategy to find, the hidden platform by the end of testing. However, LPS-treated mice displayed worse overnight forgetting of the platform location (indicated by longer swim distance on trial 1 of each day than on trial 6 of the previous day) during the early phase of training (E_ii). F. Morris Water Maze Spatial Working Learning and Memory. There were no group differences in swim distance to water escape across days and trials (F_i) nor following the two-hour delay challenge (F_ii). Mean ± SEM; * = p < 0.05; # = p < 0.10. Vehicle (Ns = 23–27) =; Intermittent LPS (Ns = 18–26) =.