PHOTORELEASE OF OXYTOCIN IN VIVO USING PHOTOSWITCHABLE NANOVESICLES MODULATES HIPPOCAMPAL CIRCUIT DYNAMICS AND SOCIAL BEHAVIOR

<jats:p> Achieving precise spatiotemporal control over neuropeptide delivery <jats:italic>in vivo</jats:italic> remains a major challenge, as conventional approaches lack temporal resolution and control over release kinetics or have limitations for <jats:italic>in vivo</jats:italic> applications. Here, we demonstrate that photoswitchable azobenzene-containing lipid nanovesicles (azosomes) enable light-controlled release of neuropeptides <jats:italic>in vivo</jats:italic> in the brain of awake moving mice. Azosomes were infused into the hippocampus via optofluidic cannulas and activated using light stimulation in freely behaving mice. <jats:italic>In vivo</jats:italic> release kinetics were systematically characterized using calcein-loaded azosomes by varying light power, pulse duration, and post-infusion time. Oxytocin (OT)-loaded azosomes were used to assess bioactivity and receptor specificity using dual-color fiber photometry with the genetically encoded OT sensor (MTRIA <jats:sub>OT</jats:sub> ), alongside pharmacological blockade with the oxytocin receptor antagonist OVTA (Ornithine-VasoTocin Analog). Azosomes enabled robust, repeatable, and light-dependent cargo release <jats:italic>in vivo</jats:italic> with tunable kinetics governed by stimulation parameters, with release efficiency controlled by light power and pulse duration. The system maintained functional stability for several hours post-infusion, with near-complete release achievable within a ~2-hour window and minimal baseline leakage prior to stimulation. Controlled OT delivery produced rapid, receptor-specific increases in MTRIA <jats:sub>OT</jats:sub> signals and modulated CA2 hippocampal circuit activity, reducing excitatory neuronal transient frequency and amplitude while altering social interaction dynamics, including decreased latency to initiate contact. These findings establish, for the first time, photoswitchable nanovesicles as a versatile platform for spatiotemporally precise delivery of neuropeptides <jats:italic>in vivo</jats:italic> , overcoming key limitations of existing delivery strategies and providing a broadly applicable framework for manipulating neuromodulatory signaling with high temporal precision. </jats:p>