Characterization of Astrocyte and Oxytocin Neuron Activity Dynamics in the Paraventricular Nucleus of the Hypothalamus

Abstract

The paraventricular nucleus of the hypothalamus (PVN) is at the axis of stress and social responses. During stress, PVN corticotropin-releasing hormone (CRH) neurons become active and release arginine vasopressin (AVP) and CRH onto downstream targets. While CRH and AVP initiate the release of glucocorticoids into the blood stream, AVP also binds to receptors on PVN astrocytes to induce calcium waves. Previous studies have found that PVN astrocyte activity is important for modulating CRH neuron activity. It has been shown that oxytocin (OXT), the social hormone, is also released in the PVN during stress to provide anxiolytic effects. We hypothesize that stress-induced OXT release in the PVN acts on PVN astrocyte receptors to provide the anxiolytic effects seen in previous studies. We sought to explore this hypothesis by using fiber-photometry on C57Bl/6 mice during a social odour preference test, freely behaving social tests, the looming shadow stress task, and the tail lift procedure. We found that PVN OXT neurons are active while a mouse sniffs another mouse and decrease in activity while a mouse sniffs an appetitive odour. We also found that PVN astrocytes are active during stressful tasks and are active moments before a mouse interacts with a non-familiar mouse. We did not see any interactions between these two cell types during our experiments. An experimental technique with a higher temporal resolution may be needed in the future to better identify if and how these two cell types interact to modulate PVN CRH neuron activity.