Psychopharmacological Properties and mechanisms of action of methanolic leaf extract of the male carica papaya linn (Caricaceae) in mice.
This study investigated the central nervous system effect of the methanolic leaf extract of the male Carica papaya, a plant reported to posses psychoactive effects. This activity was with a view to evaluate the psychopharmacological properties and mechanisms of action of the plant extract. Ninety-six adult male and female mice were divided into sixteen groups of five to six animals per group. The neuropharmacological effects of the methanolic leaf extract of the plant were evaluated by examining the effects on Novelty-induced behaviours (locomotion, rearing and grooming) of the animals. The anxiolytic effect was investigated on Elevated Plus Maze and Holeboard apparatus while its effects on learning and memory were investigated on Y-Maze. Oral doses of 125, 250 and 500 mg/kg of the extract were administered to the test group and the results were compared with the vehicle-treated control groups. Prior administration of scopolamine (3 mg/kg), a muscarinic receptor blocker, chlorpheniramine (10 mg/kg), a histamine receptor blocker and haloperidol (0.1 mg/kg) a dopamine receptor blocker were used to investigate the involvement of Cholinergic, histaminergic and Dopaminergic system in the action of the extract. The results showed that methanolic extract of dry Carica papaya leaves exhibited dose-dependent decrease in locomotor, rearing and grooming behaviours at all doses administered indicating the central inhibitory effect. Holeboard and Elevated Plus Maze tests, models showed that the extract has no anxiolytic effect, while the Y-maze model suggests that the extract has no significant effect on learning and memory. Investigation of the possible mechanism of action using scopolamine, chlorpheniramine and haloperidol showed that the dopaminergic system is highly involved in the central effect of the extract. There was indication that cholinergic components may also be involved in the action of the extract. The study concluded that the methanolic leaf extract of male Carica papaya has central inhibitory effects but no anxiolytic properties and the mechanism of action is mainly through the inhibition of the dopaminergic system.