Fig. 5.

Performance of CA3-NR1 KO mice in the standard Morris water maze task and recall capability under various cue conditions. (A to D) 18- to 24-week-old male CA3-NR1 KO mice (mutant, red, n = 44), fNR1 (blue, n = 37), Cre (n = 14, not shown), and their wild-type littermates (green, n = 11) were subjected to training trials under full-cue conditions. The four types of mice did not differ significantly in (A) escape latency, (B) distance traveled, (C) swimming velocity, or (D) time spent near the pool wall [genotype effect for each measure, F(3,102) < 2.5, P > 0.05; genotype x trial interaction for each measure, P > 0.05]. (E) Probe trials on day 2 (P1, open bars), day 7 (P2, hatched bars), and day 13 (P3, solid bars) under full-cue conditions, monitored by relative radial-quadrant occupancy [time (%) the mice spent in the target radial-quadrant relative to the total time spent in the four radial-quadrants]. On day 13, all the genotypes spent significantly more time in the target radial-quadrant than other quadrants [wild, F(3,40) = 84.1, P < 0.0001; Cre, F(3,52) = 52.7, P < 0.0001; fNR1, F(3,144) = 130.4, P < 0.0001; mutant, F(3,172) = 163.4, P < 0.0001; Newman-Keuls post hoc comparison (the trained quadrant compared to all the other quadrants); P < 0.01 for all genotypes]. (F) Day 13 probe trial (P3) of randomly selected subsets of Cre (n = 14), fNR1 (n = 20) and mutant (n = 23) mice by absolute platform occupancy [time (sec) the mice spent in the area which corresponded exactly to the area occupied by the platform during the training session] [Cre, F(3,52) = 15.8, P < 0.0001; fNR1, F(3,76) = 37.4, P < 0.0001; mutant, F(3,88) = 35.5, P < 0.0001; Newman-Keuls post hoc comparison (the target platform position compared to all the other platform positions); P < 0.01 for all genotypes]. (G) The same sets of mice as in (F) were subjected to partial-cue probe trials on day 14 (P4) and absolute platform occupancy assessed. Cre and fNR1 mice exhibited similar recall under partial-cue conditions as under full-cue conditions (paired t test, P > 0.9 for each genotype), while recall by the mutant mice was impaired (paired t test, *P < 0.01). (H) Spatial histograms of the animals’ location during the full-cue (P3) and partial-cue (P4) probe trials. fNR1, n = 20; mutant, n = 23. (I) Relative recall index [RRI, averaged ratio of the target platform occupancy of the partial-cue (P4) or no-cue (P5) probe trial to that of the full-cue (P3) probe trial for each animal (17)] of fNR1 mice (n = 18, blue) and mutant mice (n = 22, red). The RRI value difference between the fNR1 and the mutant mice under the partial-cue conditions was significant (*P < 0.009; Mann-Whitney U test), while that under no-cue conditions was not (P = 0.9; Mann-Whitney U test). T, target quadrant; AR, adjacent right quadrant; OP, opposite quadrant; AL, adjacent left quadrant.