G protein-coupled receptors (GPCRs) are the largest family of membrane receptors that activate intracellular signaling cascades and undergo endocytosis, recycling, or degradation upon stimulation. The mu, delta and kappa opioid receptors are GPCRs of the nervous system, which control pain, stress, and addictive behaviors. The delta opioid receptor (DOR-1) is the stereo selective receptor for enkephalins and inhibits neurotransmitter release by reducing calcium ion currents and increasing potassium ion conductance.
