The majority of neurotransmitter receptors are members of the G protein-coupled receptor (GPCR) superfamily. These receptors are specialized for binding a neurotransmitter, and this binding stimulates rearrangement of the protein to favor activation of intracellular signaling proteins known to bind GTP and GDP. In the GTP-bound state, the G protein is activated. Several forms of intracellular signaling proteins are affected by activated G proteins, including proteins that generate small molecule second messengers, as well as protein kinases and ion channels. Thus, G protein activation can affect neurophysiology fairly directly by altering ion channel function, and can have a long-lasting influence on neuronal function by altering intracellular signaling and even gene expression.
