Figure 4. Normal spatial memory but impaired fear-associative memory in Tspyl2 mutant mice.

(A–C), Tspyl2 mutant mice perform normally in Morris water maze (n = 7 per genotype). (A), Visual test was performed in clear water. There was no significant difference between genotypes in swim speed (p = 0.160) and latency (p = 0.613) to find the platform. (B), Spatial reference memory was tested with a fixed, hidden platform. Mutant mice learned normally. (C), Probe test was done by removing the platform after the spatial reference memory test. Wild-type and mutant mice spend similar time in the target quadrant Q2. (D), Normal pain sensation in hot plate test (n: +/Y = 15, m/Y = 5) as one of the prerequisites for fear conditioning test. (E), Results of fear conditioning tests. Mutant and wild-type mice did not differ significantly in exploratory activities during the 6 min habituation on day 1 (left). The freezing rate during habituation was shown as basal. After conditioned stimulus-unconditioned stimulus training (shock) on day 1, the mice were tested in a novel chamber with the same tone presented (cue) on day 2 and in the training chamber without tone stimulus (context) on day 3. As reflected by freezing behavior, mutant mice showed significantly impaired contextual fear conditioning (Error bars represent SEM, *p < 0.05, Student's t-test, n = 12 per group). Abbreviations: +/Y, wild-type male; m/Y, mutant male.