GPR6

Class

inverse agonist

GPR6 is an orphan G protein-coupled receptor (GPCR), meaning no endogenous activating ligand has been definitively identified, yet the receptor is constitutively active: it generates intracellular signals even without a bound ligand. GPR6 is expressed almost exclusively in a subset of striatal neurons that make up the so-called indirect pathway of the basal ganglia, a circuit that helps regulate movement. Through coupling to stimulatory G proteins, constitutive GPR6 activity raises intracellular cyclic AMP (cAMP), a second messenger that influences neuronal excitability and output. An inverse agonist binds the receptor and actively suppresses this baseline signaling, lowering cAMP below its unstimulated level, rather than simply blocking an external ligand as a neutral antagonist would. The biological rationale for targeting GPR6 centers on basal ganglia circuitry involved in motor control, particularly in contexts where dopamine signaling is disrupted, as occurs in Parkinson's disease. Because the indirect pathway becomes overactive when striatal dopamine is depleted, dampening GPR6-driven cAMP signaling in these neurons is hypothesized to help rebalance motor circuit output without directly engaging dopamine receptors. This makes GPR6 inverse agonism of interest as a non-dopaminergic strategy for movement disorders, potentially complementing existing dopamine-based approaches while avoiding some of their limitations.