Effects of oregano essential oil on brain TLR4 and TLR2 gene expression and depressive-like behavior in a rat model

The aim of the present study was to evaluate the effects of oregano essential oil (OEO) on the hippocampus and prefrontal cortex TLR 2/4 gene expression and depressive like behavior induced by chronic unpredictable stress (CUS). Sucrose preference and forced swim tests were adopted to examine the antidepressant effect. Control (CON), OEO, CUS, and CUS + OEO groups were used. The OEO and CUS + OEO groups received OEO (0.2 mL/kg, i.p.), CON and CUS received saline (0.2 mL/kg, i.p.), and the positive drug groups of CUS rats received fluoxetine (10 mg/kg) and diazepam (3 mg/kg) once daily for 14 days. The expression of TLR 2/4 was determined using real time quantitative polymerase chain reaction with the SYBR green reporter dye. The compositions of the OEO were determined by gas chromatography- mass spectroscopy. The main constituents were thymol (20.72%), gamma-terpinene (8.83%), borneol (8.72%), cymene (6.83%), carvacrol (6.274%), alfa-terpinene (5.26%), and sabinene (4.92%). Administration of OEO significantly alleviated the depressive symptoms of CUS. A higher level of TLR2/4 mRNA was seen in the brain of CUS group (P < 0.05). The CUS-induced increases in the TLR2/4 levels were not reversed by OEO. According to the present study OEO may have the antidepressant-like activity but have no effect on the stress-induced TLR-2/4 upregulation.