CRF signaling between neurons in the paraventricular nucleus of the hypothalamus (PVN) coordinates stress responses

The importance of a precisely coordinated neuroendocrine, autonomic, and behavioral stress response was a primary theme at the Stress Neurobiology Workshop 2018, held in the beautiful setting of Banff Provincial Park in Alberta, Canada. Much of the research featured at this meeting reinforced the importance of appropriately responding to stress in order to avoid various neuropsychiatric pathologies, including Post-Traumatic Stress Disorder (PTSD), depression, and addiction. Corticotropin-Releasing Factor (CRF) neurons in the paraventricular nucleus of the hypothalamus (PVN) are central players in the stress response, integrating both external and visceral stress-relevant information, then directing neuroendocrine, autonomic and behavioral adaptations via endocrine and neural outputs of the PVN. The PVN contains a densely packed array of neuron types that respond to stress, including CRF neurons that activate the Hypothalamic-Pituitary-Adrenal (HPA) axis. Recently, identification of a new population of neurons in the PVN that express CRF Receptor 1 (CRFR1) has suggested that CRF release in the PVN signals to neighboring CRF responsive neurons, potentially functioning in HPA axis feedback, neuroendocrine coordination, and autonomic signaling. Here, we review our recent work characterizing an intra-PVN microcircuit in which locally released CRF release activates CRFR1 + neurons that make recurrent inhibitory GABAergic synapses onto CRF neurons to dampen excitability, therebylimiting HPA axis hyperactivity in response to stress and promoting stress recovery, which we presented in a poster session at the conference. We then discuss questions that have arisen following publication of our initial characterization of the microcircuit, regarding specific features of intra-PVN CRF signaling and its potential role in coordinating neuroendocrine, autonomic, and behavioral outputs of the PVN. Our presented work, as well as many of the presentations at the Stress Neurobiology Workshop 2018 together establish intra-PVN signaling as an important regulatory node in stress response pathways, which are central to the pathogenesis of neuropsychiatric disorders.