Photoswitching endogenous glutamate receptors in neural ensembles and single synapses in vivo

To interrogate animal physiology in vivo, there is a lack of non-genetic methods to control the activity of endogenous proteins with pharmacological and spatiotemporal precision. To address this need, we recently developed targeted covalent photoswitchable (TCP) compounds that enable the remote control of endogenous glutamate receptors (GluRs) using light. We combine the photopharmacological effector TCP9 with neuronal activity sensors to demonstrate all-optical reversible control of endogenous GluRs across multiple spatiotemporal scales in rat brain tissue ex vivo and in Xenopus tadpole brains in vivo. TCP9 allows photoactivation of neuronal ensembles, individual neurons, and single synapses in ex vivo tissue and in intact brain in vivo, which is challenging using optogenetics and neurotransmitter uncaging. TCP9 covalently targets AMPA and kainate receptors, maintaining their functionality and photoswitchability for extended periods (> 8 h) after a single compound application. This allows tracking endogenous receptor physiology during synaptic plasticity events such as the reduction of functional AMPA receptors during long-term depression in hippocampal neurons. TCP9 is a unique non-invasive tool for durable labeling, reversible photoswitching, and functional tracking of native receptors in brain tissue without genetic manipulation.