Features:hM4Di is an engineered receptor (DREADD) derived from the human muscarinic acetylcholine receptor M4 (hM4D) that responds only to CNO and is no longer activated by acetylcholine. In certain neurons, CNO binding to hM4D activates Gi protein-coupled inward potassium channels (GIRK), leading to cell membrane hyperpolarization and inhibition of neuronal action potential firing.