Abstract
Origanum majorana (L.) is an herb used in the treatment of diseases related to the nervous system in traditional medicine (e.g. as an anticonvulsant and sedative). The present study was conducted to investigate the antidepressant-like effects of Origanum majorana essential oil (OMEO) on mice in the forced swimming test (FST). The animals were intraperitoneally (i.p.) injected with OMEO (10-80 mg/kg) 1 h before the FST. To assess the involvement of the monoaminergic system in the antidepressant activity of OMEO, different pharmacological antagonists were administered 15 min before OMEO administration (80 mg/kg). The administration of OMEO (40 and 80 mg/kg, i.p.) decreased immobility time and increased swimming and climbing times significantly. OMEO did not cause any changes in spontaneous locomotor function in the open-field test (OFT). The pre-treatment of the animals with SCH23390, sulpiride, haloperidol, WAY100135, p-chlorophenylalanine (pCPA), ketanserin, prazosin, yohimbine, reserpine, but not propranolol, inhibited the anti-immobility effect of OMEO in the FST. A combination of sub-effective doses of fluoxetine (5 mg/kg, i.p.) or imipramine (5 mg/kg, i.p.) with OMEO (10 mg/kg, i.p.) increased the antidepressant-like effects. OMEO showed antidepressant-like effects through involvement with the dopaminergic (D1 and D2), serotonergic (5HT1A, 5-HT2A receptors) and noradrenergic (α1 and α2 adrenoceptors) systems.