Limonene has anti-anxiety activity via adenosine A2A receptor-mediated regulation of dopaminergic and GABAergic neuronal function in the striatum

Limonene, a common terpene found in citrus fruits, is assumed to reduce stress and mood disorders. Dopamine and γ-aminobutyric acid (GABA) have been reported to play an important role in modulating anxiety in different parts of the brain. Herein, we report the anxiolytic activity of limonene. In addition, we identified a possible mechanism underlying the effect of limonene on DAergic and GABAergic neurotransmission. In this study, mice were injected with saline in the control group and limonene in the test group before behavioral analysis. We performed immunoblotting and high-performance liquid chromatography (HPLC) analysis after the behavioral study. The limonene treated group showed increased locomotor activity and open-arm preference in the elevated plus maze experiment. Limonene treatment increased the expression of both tyrosine hydroxylase and GAD-67 proteins and significantly upregulated dopamine levels in the striatum. Furthermore, tissue dopamine levels were increased in the striatum of mice following limonene treatment, and depolarization-induced GABA release was enhanced by limonene pre-treatment in PC-12 cells. Interestingly, limonene-induced anxiolytic activity and GABA release augmentation were blocked by an adenosine A2A receptor (A2AR) antagonist. Our results suggest that limonene inhibits anxiety-related behavior through A2A receptor-mediated regulation of DAergic and GABAergic neuronal activity.