Serotonin 1B knockout mice exhibit a task-dependent selective learning facilitation.

Serotonin 1B knockout (KO) mice exhibit better spatial reference memory performance in the Morris water maze than their wild type (WT) controls. The present study was aimed at dissecting the underlying cognitive bases of this facilitation using a stepwise water maze paradigm. The performance of KO mice did not differ from WT in a single start-goal task, nor when using two opposite starts. However, KO mice exhibited better performance in stages requiring cognitive flexibility or the higher level of spatial navigation planning (standard version). In a short-term memory version of the task, no such genotype effect was observed, confirming our previous findings. These results suggest that the serotonin 1B receptor gene deletion selectively enhances learning performance when the cognitive requirement of the task is elevated.