Project Summary (Project 4, Co-PIs: Buzsaki, Froemke, Lin, Tsien) The spatiotemporal scales of oxytocin (OXT) modulation in the central nervous system remain unclear, and the actions on downstream targets and mechanisms of upstream control are poorly understood especially compared to other modulators. Here we measure signals from next-generation modulatory GRAB sensors. Our pilot data established that OXT levels fluctuate extensively during both overt waking behaviors and sleep, reaching its minimum during REM sleep. Thus OXT release occurs not only during social behaviors but in other contexts as well. Therefore, the goal of Project 4 is to ask how a) OXT neurons are regulated by upstream brain regions, involved in a variety of behaviors, and how b) OXT affects specific network computations in target areas. We will also relate its actions to a well-characterized neuromodulator, acetylcholine (ACh) and address how artificial (“pathological”) coupling between OXT and specific circuit patterns during sleep impacts waking social behavior. In the first set of experiments, we will identify paradigm-independent physiological features of subtypes of OXT neurons and relate them to paradigm-specific (e.g., parental behavior, social hierarchy) behaviors. Potential OXT subtypes (assessed with mouse lines generated by the Molecular Tools Core via intersectional approaches) will be identified optogenetically, with by physiological and brain state-dependent characterization. Using large-scale electrophysiological methods, we will establish the relationship between the firing patterns of OXT neuron types and characteristic population patterns in the hippocampus, thalamus and neocortex. In turn, these characterized firing patterns will serve to relate their spiking activity observed during social interactions and maternal care. The second set of experiments are devoted to reveal the differential impact of OXT neurons in the paraventricular and supraoptic nuclei on their target circuit patterns and compare these effects to those of a different modulator (here, ACh). We will examine the influence of neuromodulation on critical hippocampal (theta, gamma, sharp wave ripples) and neocortical (gamma, UP-DOWN states) network patterns and inter- regional communication. We will also establish the state-dependent temporal relationships between OXT and ACh. The final set of experiments will artificially alter the temporal relationship between REM and non-REM patterns in the hippocampus and OXT release. The goal of these experiments is to gain knowledge how potential sleep patterns might be required for social learning and memory over extended interactions between animals, and if specific perturbations of these mechanisms impact subsequent social behavior in the waking animal. In sum, this project aims to discover the network control of OXT and its impact on circuits, and compare the conditions and circuit mechanisms distinguishing non-social vs social aspects of OXT sign...