The Effects of Melatonin, Fluoxetine and Their Combinations on Stress Induced Behavioral and Cognitive Impairments in Mice

Abstract

Objective: Melatonin (Mel) is a hormone with anti-depressant and anti-oxidant features. It is well known that melatonin protects brain cells from reactive oxygen species and that the brain's high oxygen consumption and lipid content make it particularly vulnerable to oxidative stress caused by prolonged stress. This study aims to investigate the effects of melatonin, fluoxetine and their combinations on emotional memory, depression, and anxiety-like behavioral changes induced by immobilization (Imb) stress. Material and Method: 48 male Balb/c mice were divided into eight groups: Cnt (control), Imb, Imb+Mlt, Imb+Flx (fluoxetine), Imb+Mlt+Flx, Mlt, Flx and Mlt+Flx. For seven days in a row, the mice underwent daily immobilization stress for 6 hours. Mice were treated with Mlt (10 mg/kg) and Flx (20 mg/kg). All animals were subjected to the behavioral tests; forced swimming test (FST), open field test (OFT), elevated plus maze (EPM), passive avoidance test (PAT) and hot plate (HP) test. After all behavioral tests, brain tissues were obtained for malondialdehyde level analysis. Result and Discussion: OFT test data showed the time spent in the central zone and the number of entrances to the central area were significantly lower in the Imb group compared to the Cnt group, these were higher in the Imb+Flx, Imb+Mlt, Imb+Mlt+Flx groups compared to the Imb group. Also, according to the data obtained from FST, immobile time was significantly higher in the Imb group compared to the Cnt group, it was lower in the Imb+Flx, Imb+Mlt, Imb+Mlt+Flx groups compared to the Imb group. Besides, it was demonstrated that the emotional memory index was statistically higher in the Imb group compared to the Cnt group, and the increasing of memory index returned to normal in the Imb+Mlt and Imb+Mlt+Flx groups with PAT. And also, lipid peroxidation level, which increased in the Imb group, decreased significantly in the Imb+Flx, Imb+Mlt, and Imb+Mlt+Flx groups. As a result, it was observed that melatonin has anti-depressant, anxiolytic, antioxidant effects and normalized emotional memory. Also, melatonin, fluoxetine and their combinations exert similar effects in the present study.