Social relationships are essential for a healthy human life, where relationships between mates (pair bonds) and between parents and offspring provide both physical and psychological benefits for the individuals involved. Oxytocin (OXT) and vasopressin (AVP) are two neuropeptides that modulate these social behaviors, both in humans and the animal model of interest, the prairie vole (Microtus ochrogaster), a small rodent that mates for life and exhibits both maternal and paternal care. However, OXT and AVP neuronal populations in key regions of the brain regulating social behavior have not yet been characterized in prairie voles. This study seeks to locate and identify OXT and AVP neuronal cell bodies and axons in these social brain regions. In addition, we will confirm the presence or absence of synapses and investigate whether OXT neurons interact with AVP producing neurons, and whether cells may express both neuropeptides. Preliminary data from fluorescence imaging suggests OXT and AVP are expressed in different populations of neurons. Furthermore, fluorescence images show OXT may modulate AVP neurons. Preliminary electron microscopy data confirm that OXT expressing neurons produce synapses onto neurons in the paraventricular nucleus of the hypothalamus (PVN), a critical brain region producing these neuropeptides. Future research will continue characterization of the circuitry of OXT and AVP with special attention to the PVN. Overall, this study will provide a better understanding of the anatomy of these systems in a species that actively displays the highly affiliative behaviors seen in humans and will facilitate future research using this animal model.