Impairment of cognitive flexibility in type 2 diabetic db/db mice.

•Type 2 diabetic db/db mice show impaired cognitive flexibility.•Immobility and slow swim speed in db/db mice may affect behavioral outcomes.•Path efficiency of Morris water maze is useful for cognitive testing of db/db mice.•Db/db mice show shortening of axon initial segment at 10 and 26 weeks of age.•Db/db mice show elongation of nodes of Ranvier at 26 weeks of age.