Abstract

Glycyrrhizae radix (licorice) comprises a variety of flavonoids as major constituents including isoliquiritigenin, liquiritin, liquiritigenin, and glycyrrihizin. It has shown various biological activities such as anti-inflammatory, anti-carcinogenic and antihistamic. As very little is known in regard to drug addiction, we carried out a study on the effect of G. radix and its active component, isoliquiritigenin, on acute cocaine-induced extracellular dopamine release in moving rats. Male Sprague–Dawley rats were orally administered with methanolic extracts of G. radix or isoliquiritigenin 1 h prior to an injection of cocaine (20 mg/kg, intraperitoneal (i.p.)). Extracellular dopamine was measured by in vivo microdialysis. Extract of G. radix and isoliquiritigenin inhibited cocaine-induced extracellular dopamine level in the nucleus accumbens by dose-dependent manner. Inhibition of dopamine release by isoliquiritigenin resulted in attenuation of the expression of c-Fos, an immediately early gene induced by cocaine. Effect of isoliquiritigenin was completely prevented by a GABA_B receptor antagonist. Thus, these results showed that G. radix and isoliquiritigenin inhibit cocaine-induced dopamine release by modulating GABA_B receptor, suggesting that isoliquiritigenin might be effective in blocking the reinforcing effects of cocaine.

Keywords: Isoliquiritigenin; Cocaine; Nucleus accumbens; G. radix (licorice)

Article Outline

1. Introduction

2. Materials and methods

2.1. Preparation of methanolic extracts of G. radix and isoliquiritigenin

2.2. Animals

2.3. Microdialysis

2.4. Measurement of extracellular dopamine

2.5. c-Fos immunohistochemical staining

2.6. Statistical analysis

3. Results

3.1. Effects of isoliquiritigenin on cocaine-induced extracellular dopamine level in rat brain

3.2. SCH 50911 blocked isoliquiritigenin's inhibition effect on cocaine-induced dopamine level

4. Discussion

Acknowledgements

References