The neurotransmitter glutamate activates not only ionotropic receptors
, which mediate fast excitatory synaptic transmission, but also metabo
tropic receptors. The latter form a large, heterogeneous family of G p
rotein-coupled receptors with specific functions in normal as well as
in pathological situations. The diverse cellular responses mediated by
metabotropic glutamate receptors and their distinct expression patter
ns in different brain systems render these receptors potential drug ta
rgets with a variety of possible mechanisms of action.