Glutamate is a main excitatory neurotransmitter in the central nervous system, and it plays a role in learning, memory and neurotoxicity. The biological actions of glutamate are mediated by ionotropic and metabotropic glutamate receptors, which are ion channels and GPCRs respectively. Metabotropic glutamate receptors (mGluRs) are members of the class 3 G-protein coupled receptor family, which are characterized by a large extracellular domain. They are further classified into group I, II, and III mGluRs on the basis of their sequence identity, pharmacology, and signal transduction mechanism. Group I (mGlu1 and mGlu5) couple to the phospholipase C pathway through Galphaq, whereas group II (mGlu2 and mGlu3) and group III (mGlu4 , mGlu6 , mGlu7 , and mGlu8) negatively couple to the adenylyl cyclase pathway though Galphai. The mGlu1 has been implicated in neurodegeneration, as indicated by a decrease in the mGlu1 signaling in the cerebral cortex of Alzheimer"s disease and dementia with Lewy bodies. In addition, studies with pharmacological inhibitors of mGlu1 and mGlu1 knockout mice indicate a role for mGlu1 in prepulse inhibition, motor and spatial learning, and anxiety.