Abstract

Ethnopharmacological relevance Mitragyna speciosa (Korth.) Havil. (M. speciosa) is among the most well-known plants used in ethnic practice of Southeast Asia. It has gained increasing attention as a plant with potential to substitute morphine in addiction treatment program. However, its action on the central nervous system is controversial.

Aim of the study This study investigated the effects of M. speciosa alkaloid extract on naloxone-precipitated morphine withdrawal and neural signaling in the nucleus accumbens (NAc, brain reward center) of mice.

Materials and methods The effects of M. speciosa alkaloid extract and mitragynine, a pure major constituent, on naloxone-precipitated morphine withdrawal were examined. Male Swiss Albino (ICR) mice were rendered dependent on morphine before injection with naloxone, a nonspecific opioid antagonist, to induce morphine withdrawal symptoms. The intensity of naloxone-precipitated morphine withdrawal was assessed from jumping behavior and diarrhea induced during a period of morphine withdrawal. To test possible addictive effect of M. speciosa alkaloid extract, mice were implanted with intracranial electrode into the NAc for local field potential (LFP) recording. Following M. speciosa alkaloid extract (80 mg/kg) and morphine (15 mg/kg) treatment, LFP power spectra and spontaneous motor activity were analyzed in comparison to control levels.

Results One-way ANOVA and multiple comparisons revealed that M. speciosa alkaloid extract (80 and 100 mg/kg) significantly decreased the number of jumping behavior induced by morphine withdrawal whereas mitragynine did not. Additionally, M. speciosa alkaloid extract significantly decreased dry and wet fecal excretions induced by morphine withdrawal. LFP analysis revealed that morphine significantly decreased alpha (9.7–12 Hz) and increased low gamma (30.3–44.9 Hz) and high gamma (60.5–95.7 Hz) powers in the NAc whereas M. speciosa alkaloid extract did not. Spontaneous motor activity was significantly increased by morphine but not M. speciosa alkaloid extract.