Learning performance in the Morris water maze. (A) In
the first part of the experiment, WT (+/+, n =
40), HET (+/−, n = 43), and KO (−/−,
n = 39) mice received 12 blocks of training (3
blocks of 4 trials per day for 4 consecutive days) in the hidden
platform version of the maze. The graph shows the escape latency to
find the hidden platform for each genotype over successive blocks of
trial. Thereafter, each animal was given 4 blocks of the visible
platform test (n = 18, 18, and 20 for WT, HET, and
KO, respectively). (B) During the probe trial after the
twelfth block of training, WT mice spent significantly more time at the
trained quadrant no. 1 (49.5 ± 2.4%, n = 40)
than did KO mice (32.8 ± 2.4%, n = 39), and
HET mice displayed an intermediate performance (37.4 ± 2.2%,
n = 43) (one-way ANOVA, P <
0.001). Means ± SEM are given.