Rabbit Anti-Human GRM3 polyclonal antibody for IHC-P. Glutamate receptors constitute the principal excitatory neurotransmitter receptors in brain. Two classes of glutamate receptors exist: ionotropic receptors, and metabotropic receptors. Ionotropic glutamate receptors are oligomeric complexes of various subunits (GluR1-7, NMDA1-3, KAI-2) , which comprise ligand-gated calcium channels. Metabotropic glutamate receptors are G-protein coupled receptors, which when activated can activate phopholipases or adenylylcyclase, depending on the neuron.