*3.1. Tryptophan-Containing Dipeptides Improved Memory Impairment in Amnesic Mice*

To evaluate the effects of the WY, WM, WV, WL, and WF dipeptides, which are known to be derived from milk proteins, on spatial memory, amnesia was induced by treatment with scopolamine, a muscarinic antagonist, according to a previous study [7]. The spontaneous alternation test using the Y-maze is well-established as a behavioral evaluation method for examining short-term spatial memory performance. A single dose of 1 mg/kg WY, WM, WV, WL, or WF dipeptide significantly increased the spontaneous alternation (Figure 1A–E, respectively). Further, the administration of 0.3 mg/kg WY or WM dipeptide already increased the alternation, which showed higher improvement than that of WV, WL, or WF (Figure 1A and B). The number of arm entries was not changed among the groups (data not shown). These results indicated that the administration of certain dipeptides with N-terminal tryptophan improved short-term spatial memory in amnestic mice.

**Figure 1.** The effects of dipeptides (**A**) WY, (**B**) WM, (**C**) WV, (**D**) WL, and (**E**) WF on spatial memory in amnesic mice. Six-week-old Crl:CD1 male mice were orally administered 0, 0.3, or 1 mg/kg of dipeptide (WV, WM, WV, WL, and WF) and, 40 min later, injected intraperitoneally with 0.85 mg/kg of scopolamine. At 1 h after oral administration, each mouse was allowed to explore the Y-maze for 8 min. Spontaneous alternations were also measured. Data represent the mean ± SEM of 10 mice per group. The *p* values shown were calculated using the Dunnett's test. \**p* < 0.05 and \*\**p* < 0.01.
