(A–C) Ngl3−/−(Hyb) mice (2–4 months) display impaired spatial learning and memory in learning (days 1–7), probe (days 8 and 14), and reversal (days 9–13) phases of the Morris water maze test (days 1–14). Quadrant occupancy and number of crossings over the location of the former platform during the probe phase on day 8 (B) and on day 14 after the completion of reversal learning (C) are also indicated. n = 11 mice for WT and 12 for KO; *P < 0.05, **P < 0.01, ***P < 0.001, ns, not significant, repeated measure of ANOVA, Student t test, and Mann-Whitney test. (D–F) Ngl3−/−(B6) mice (2–4 months) display impaired spatial learning and memory in learning (days 1–7), probe (days 8 and 14), and reversal (days 9–13) phases of the Morris water maze test (days 1–14). Quadrant occupancy and number of crossings over the location of the former platform are indicated for the probe phases on day 8 after the completion of the initial learning phase (B) and on day 14 after the completion of the reversal learning phase (C). n = 10 mice for WT and 5 for KO; **P < 0.01, ***P < 0.001, ns, not significant, repeated measure of ANOVA and Student t test. Primary data can be found in S3 Data. KO, knockout; KO-B, knockout, C57BL/6; KO-H, knockout, hybrid; L, left; ns, not significant; O, opposite; R, right; T, target quadrant; WT, wild-type.