Abstract The physiological activity of proteins is often studied with loss-of-function genetic approaches, but the corresponding phenotypes develop slowly and can be confounding. Photopharmacology allows direct, fast and reversible control of endogenous protein activity, with spatiotemporal resolution set by the illumination method. Here, we combine a photoswitchable allosteric modulator (alloswitch) and two-photon excitation (2PE) using pulsed near-infrared lasers to reversibly silence mGlu 5 receptor activity in intact brain tissue. Endogenous receptors can be photoactivated in neurons and astrocytes with pharmacological selectivity and with an axial resolution between 5 and 10 μm. Thus, two-photon pharmacology (2PP) using alloswitch allows investigating mGlu 5 -dependent processes in wild type animals, including synaptic formation and plasticity, and signaling pathways from intracellular organelles.