*3.3. WY Peptide Increased Dopamine Levels in the Hippocampus and Frontal Cortex*

Because we previously reported that the GTWY peptide inhibits MAO-B activity in vitro and in vivo and increases dopamine contents in the frontal cortex and hippocampus, we further evaluated the effect of the WY dipeptide on the catecholamine levels in the hippocampus and frontal cortex. In both the hippocampus and frontal cortex, a single administration of the WY dipeptide significantly increased the level of dopamine (Figure 3A–F). The levels of DOPAC and HVA appear to be slightly increased, though not statistically significant. Thus, the administration of WY dipeptide increased the level of dopamine in the brain without affecting the levels of its metabolites.

**Figure 3.** The levels of dopamine and its metabolites in the hippocampus and frontal cortex. Six-week-old Crl:CD1 male mice were orally administered 0 or 1 mg/kg of WY dipeptide. At 1 h after oral administration, the following monoamine levels were measured in the hippocampus (**A**–**C**) and frontal cortex (**D**–**F**) by HPLC: dopamine (DA) (**A**, **D**), 3,4-dihydroxyphenylacetic acid (DOPAC) (**B**, **E**), and homovanillic acid (HVA) (**C**, **F**). Data represent the mean ± SEM of 10 mice per group. The *p* values shown were calculated using the Student's *t*-test. \* *p* < 0.05.
