Antidepressant-Like Activity of Solvent Fractions of the Root Bark of Carissa spinarum Linn. (Apocynaceae) in Rodents Involves Multiple Signaling Pathways

BACKGROUND: The root bark of Carissa spinarum Linn. (Apocynaceae) is claimed to be used for the management of depression in Ethiopian folkloric medicine, and the crude extract has been reported to possess antidepressant-like activity in rodents. OBJECTIVE: This study aimed to evaluate the antidepressant-like effect of different fractions of the root bark in rodents and the possible underlying mechanisms in rats. METHODS: A 70% ethanol extract of the root bark was successively fractionated with n-butanol, ethyl acetate, and water. Animals of both sexes received 2% Tween 80, imipramine (30 mg/kg), or various doses (50, 100, 200 mg/kg) of the fractions. Duration of immobility was determined using the tail suspension test and the forced swim test. Locomotor activity was evaluated in the open field test. Serum corticosterone levels, total phenols, flavonoids, and alkaloids were determined. Preliminary mechanistic studies were also performed to explore possible mechanisms of action of the active fraction. RESULTS: All fractions but the aqueous fraction significantly (p<0.001) decreased the duration of immobility in both tests, with the ethyl acetate fraction being the most active. The locomotor test revealed that the activity was not due to non-specific psycho-stimulant effects. Serum corticosterone levels were reduced by both fractions, with the ethyl acetate fraction again being the most effective. Mechanistic studies showed the involvement of multiple neurotransmission systems, including adrenergic, dopaminergic and cholinergic as well as L-Arginine-NO-cGMP pathway. Higher contents of phenols (42.42 vs 29.8 mgGAE/g), flavonoids (12.43 vs 2.07 mgQE/g), and alkaloids (0.17 vs 0.07 mgATE/g) were found in the ethyl acetate than in the n-butanol fraction. CONCLUSION: The present findings collectively indicate that the ethyl acetate and n-butanol fractions are endowed with antidepressant-like activity due to the presence of phenols, flavonoids, and alkaloids, which are medium polar in nature.