Background information
Glutamate is the main excitatory neurotransmitter in the brain. For many years it had been considered to act only on the ligand-gated receptor channels-termed NMDA, AMPA and kainite receptors that are involved in the fast excitatory synaptic transmission. Recently, glutamate has been shown to regulate enzymes producing second messengers via specific receptors coupled to G-proteins. These receptors are called metabotropic glutamate receptors. In expression systems, Group-I receptors stimulate phospholipase C as revealed by an increase in phosphoinositide turnover and calcium release from internal stores. Group-II and -III receptors are coupled to the inhibition of adenylyl cyclase. The Group-I receptors include Metabotropic Glutamate Receptor 5 and Metabotropic Glutamate Receptor 1a. The Group-II receptors in include mGluR2 and mGluR3.
