Hypothalamic CRH neurons in stress induced psychopathology: revaluation of endocrine and neural mechanisms

Stress has a strong influence on mental health around the world. Decades of research have sought to identify mechanisms through which stress contributes to psychiatric disorders such as depression, to potentially guide the development of therapeutics targeting stress systems. The hypothalamic pituitary adrenal (HPA) axis has been the focus of much of this research, as the key endocrine stress response system that is responsible for coordinating the changes throughout the body that necessary for survival under stress. Corticotrophin releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) sit at the apex of the HPA axis, integrating signals relevant to stress and external threats, to ensure HPA axis activity is appropriate for the given context. In addition to this, emerging research has demonstrated that neural activity in PVN-CRH neurons regulates stress related behaviours via modulation of downstream synaptic targets. This review will summarize convergent evidence from preclinical studies on chronic stress and clinical research in mood disorders demonstrating changes in PVN-CRH neural function, consider how this may influence synaptic targets of PVN-CRH neurons, and discuss the potential role of these PVN-CRH synaptic pathways in the development of maladaptive behaviours following chronic stress that are relevant to depression. We will also highlight important questions for future research aimed at precisely dissecting endocrine and synaptic roles of PVN-CRH neurons in chronic stress, their potential interactions, and therapeutic opportunities for the treatment of stress related disorders.