Sex Differences in Major Depressive Disorder (MDD) and Preclinical Animal Models for the Study of Depression

Depression and related mood disorders constitute an enormous burden on health, quality of life, and the global economy, and women have roughly twice the lifetime risk of men for experiencing depression. Here, we review sex differences in human brain physiology that may be connected to the increased susceptibility of women to major depressive disorder (MDD). Moreover, we summarize decades of preclinical research using animal models for the study of mood dysfunction that uncover some of the potential molecular, cellular, and circuit-level mechanisms that may underlie sex differences and disease etiology. We place particular emphasis on a series of recent studies demonstrating the central contribution of the circuit projecting from ventral hippocampus to nucleus accumbens and how inherent sex differences in the excitability of this circuit may predict and drive depression-related behaviors. The findings covered in this review underscore the continued need for studies using preclinical models and circuit-specific strategies for uncovering molecular and physiological mechanisms that could lead to potential sex-specific diagnosis, prognosis, prevention, and/or treatments for MDD and other mood disorders.