Fig. 4
From: Rodent models for psychiatric disorders: problems and promises
Cell-type specific neuromodulation can be achieved using specialized ligand-activated or light-activated receptors. Chemogenetics (A) involves using designer receptors exclusively activated by designer drugs (DREADDs) which are generally modified human muscarinic G-protein coupled receptors. Selective activation of DREADDs via clozapine N-oxide (CNO) or compound-21 (C21) can produce excitatory effects through Gq (hM3Dq) and Gs (GsD) pathways which increase calcium and cyclic adenosine monophosphate (cAMP), respectively. Alternatively, inhibitory effects can be achieved using Gi (hM4Di) signaling, which reduces cAMP levels. Optogenetics (B) utilizes light-activated rhodopsin channels which can produce excitatory effects through sodium currents (Channelrhodopsin; ChR2) or inhibitory effects through chloride currents (Halorhodopsin; NpHR). Excitatory or inhibitory effects can also be achieved through light-activated Gq, Gs, or Gi signaling (OptoXR)