Photocaged Oxytocin and Vasopressin Probes to Decipher Neuropeptide Signalling With High Spatiotemporal Resolution

The oxytocin/vasopressin (OT/VP) neuropeptide signalling system is essential for regulating social behaviour, emotion, learning, and memory, and its dysregulation is associated with multiple neurological disorders. However, accurately studying OT/VP signalling in the brain remains difficult due to widespread receptor expression, long peptide half-lives, and extensive diffusion. To address these challenges, we investigated three classes of photolabile protecting groups-coumarin, nitrophenylpropyl, and borondipyrromethene-to enable precise, light-triggered OT/VP release. These photocages allow controlled activation with one-photon (365-527 nm) or two-photon (730-780 nm) irradiation and do not generate cytotoxic by-products. Using these cages, we synthesised OT/VP photoprobes and characterised their photopharmacological properties at their neuronal receptors (OTR, V1aR, V1bR). The coumarin cage proved the most effective, suppressing OT/VP bioactivity until rapid photouncaging enabled on-demand receptor activation. It excelled in cellular assays, primary rat hippocampal neurones, and ex vivo acute mouse brain slices, demonstrating broad applicability. It is biocompatible, readily incorporated into peptides, and compatible with various neuronal experimental setups. Photo-uncaging can be performed with inexpensive light-emitting diode (LED) setups, as well as with extreme precision via two-photon excitation, enabling investigations of neuropeptide signalling with high spatiotemporal resolution, offering new opportunities to investigate neuropeptide function in health and disease.