BDNF and stress-related disorder: Many biomarkers were studied like oxytocin level, leptin level, brain-derived neurotrophic factor (BDNF), and luteinizing hormone : follicular stimulating hormone ratio, but the oxytocin level is the best-studied brain system in humans with vast growing evidence showing its effect on social perception, behavior, and social memory, the amygdala, and stress-related disorders [9–14].