Abstract:
Historically neurotransmitter receptor classes have been divided into two categories: ionotropic and metabotropic. Ionotropic receptors are typically multi-subunit structures that when activated conduct ions through a central pore, leading directly to the depolarization/hyperpolarization of the plasma membrane, generation of action potentials, and release of neurotransmitters from axon terminals. Metabotropic receptors on the other hand are single protein, seven transmembrane domain structures (though multi-subunit complexes like the GABAB receptor exist), which upon binding of a ligand, activate specialized sets of second messenger proteins such as the heterotrimeric guanosine nucleotide binding proteins (G proteins). These proteins upon activation translocate to other parts of the cell where they regulate a host of downstream signaling molecules such as adenylyl cyclase and phospholipase C, gene signaling cascades such as the ERK/MAPK pathway, and cytoskeletal regulatory pathways underlying neurite growth and development. In recent years a number of studies have come out demonstrating that these two receptor classes may not be as functionally distinct as was formerly thought.
