Gamma Oryzanol Alleviates High-Fat Diet-Induced Anxiety-Like Behaviors Through Downregulation of Dopamine and Inflammation in the Amygdala of Mice.

A high-fat diet (HFD) can induce obesity and metabolic disorders that are closely associated with cognitive impairments, and the progression of several psychiatric disorders such as anxiety. We have previously demonstrated the anxiolytic-like effect of Gamma oryzanol (GORZ) in chronic restraint stressed mice.We studied the neurochemical and molecular mechanisms that underlie the preventive effect of GORZ in HFD-induced anxiety-like behaviors, monoaminergic dysfunction, and inflammation.

Eight-week-old Institute of Cancer (ICR) male mice weighing 33-34 g were divided into the following groups and free-fed for 8 weeks: control (14% casein, AIN 93M); HFD; HFD + GORZ (0.5% GORZ). Body weight gain was checked weekly. The anxiolytic-like effects of GORZ were examined via open-field test (OFT) and elevated plus maze (EPM) test. Brain levels of monoamines [5-hydroxy tryptamine (5-HT), dopamine (DA), and norepinephrine (NE)] and their metabolites [5-hydroxyindole acetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG)], proinflammatory cytokines such as tumor necrosis factor-αα (Tnf-α) mRNA levels, and interleukin 1-β (Il-1β) mRNA levels in the cerebral cortex and amygdala were examined using high-performance liquid chromatography-electrochemical detection (HPLC-ECD), and real-time reverse transcription-polymerase chain reaction (RT-PCR), respectively.

Mice fed a HFD for eight weeks showed anxiety-like behaviors in association with HFD-induced body weight gain. GORZ potentially blocked HFD-induced anxiety-like behaviors via significant improvement of the primary behavioral parameters in behavioral tests, with a minor reduction in HFD-induced body weight gain. Furthermore, GORZ treatment significantly downregulated HFD-induced upregulation of dopamine levels in the brain's amygdala. Significant reduction of the relative mRNA expression of Tnf-α and Il-1 β was also observed in the amygdala of HFD + GORZ mice, compared to HFD mice.

Our findings strongly suggest that 0.5% GORZ exerts anxiolytic-like effects, possibly through downregulation of dopamine, and via expression of proinflammatory cytokines Tnf-α and Il-1 β in the case of chronic HFD exposure.