Glutamate is a major excitatory neurotransmitter of the CNS. The diversity of glutamate is exemplified by two distinct groups of receptors: ionotropic and metabotropic. Ionotroic receptors are ligand-gated cation channels. They can be subdivided into two classes: NMDA and AMPA/kainate receptors. GluR δ2 exhibits only 25% amino acid identity to either ionotropic receptor type. It presents selective and abundant exression in cerebellar Purkinje cells. It is targeted to a subset of Purkinje cell spines and is coexpressed with ionotropic receptors. GluR δ2 is involved in motor coordination, Purkinje cell synapse formation, and cerebellar long-term depression (LTD). The latter is a decrease in the efficacy of the synaptic transmission between parallel fibers and Purkinje neurons and is a cellular basis of motor learning. In fact, mGluR δ2-deficient mice lack LTD. Additionally, an amino acid substitution in transmembrane III of δ2 is responsible for the neurodegeneration seen in Lurcher mice. This substitution is a gain of function mutation that results in disruption of Purkinje membrane potential. Thus, GluR δ2 is an important regulatory component of the Purkinje GluR channel.