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

Background: 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.

Hypothesis/purpose: 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.

Study Design: 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.

Results: 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.

Conclusion: Our results suggest that limonene inhibits anxiety-related behavior through A2A receptor-mediated regulation of DAergic and GABAergic neuronal activity.