Chemogenetics (DREADDs)

Chemogenetics controls genetically-targeted cells with an otherwise-inert small molecule. The dominant tools are DREADDs — Designer Receptors Exclusively Activated by Designer Drugs — engineered muscarinic G-protein-coupled receptors that no longer respond to acetylcholine but are activated by a pharmacologically inert ligand. The excitatory hM3Dq couples through Gq to depolarise, the inhibitory hM4Di couples through Gi to silence, and Gs-coupled and kappa-opioid-derived variants allow independent, multiplexed control of separate populations.

Compared with optogenetics, chemogenetics trades temporal precision for reach and convenience: a single systemic dose modulates an entire genetically-defined population across the whole brain for minutes to hours in a freely-moving animal, with no implanted hardware. That profile — scalable, chronic, and using drug-like ligands — makes it the neuromodulation approach most often discussed for eventual clinical translation.