In vivo photoreversible neuromodulation with infrared light

Photoswitchable ligands enable reversible control of receptor function by photoisomerization between two conformations having different biological activity. Shifting the operating wavelengths of photoswitchable ligands towards the red and infrared (IR) spectrum, while maintaining thermodynamically stable isomers, has been pursued to reduce phototoxicity and to increase photosensitivity. However, no photoswitchable ligands have been reported that support bidirectional switching with IR light under physiological conditions, which would further allow deep tissue penetration in vivo. We have developed a set of photoswitchable compounds targeting muscarinic receptors, named neuroswitches, that optimally respond to IR light. These compounds can be operated by conventional one-photon as well as by two-photon excitation (2PE) to remotely activate receptor signaling. Importantly, bidirectional 2PE was achieved with IR wavelengths between 730 nm and 910 nm, allowing the activation and deactivation of receptor signaling in vitro and enabling effective and reversible neuromodulation of the brain cortex of wild-type mice. Neuroswitches therefore offer the opportunity to study and manipulate intact receptor activity in vivo with unprecedented pharmacological and spatiotemporal selectivity, while minimizing phototoxicity. They support the development of novel non-invasive phototherapies based on muscarinic neuromodulation, offering the promise of a single-component drug that is intrinsically devoid of adverse effects in the dark and could be photoactivated on demand in selected cortical regions to improve treatment efficacy, safety, and versatility.