Immunoprecipitation, immunoblotting, and immunocytochemistry studies suggest that glutamate receptor delta subunits form novel postsynaptic receptor complexes.

An antibody was made to a C-terminus peptide of the glutamate receptor delta 2 subunit and used to study the distribution, biochemical properties, and developmental expression of the delta receptor in rat brain. The antibody recognizes both delta 1 and delta 2 but not AMPA, kainate, NMDA, and mGluR1 alpha glutamate receptor subunits based on Western blot analysis of transfected HEK-293 cells. Western blot analysis of brain showed a single immunoreactive band, migrating at M(r) = 114,000. Immunoprecipitation of detergent-solubilized cerebellar membranes was done to determine if delta is associated with other glutamate receptor subunits and if it binds any of the common excitatory amino acid ligands. Based on results of these studies, AMPA, kainate, NMDA, and mGluR1 alpha subunits do not coassemble with delta subunits, and 3H-glutamate, 3H-AMPA and 3H-kainate do not bind to the delta receptor complex. Western blot and immunocytochemical analyses showed marked expression of delta in the cerebellum while lower levels were detected in other regions of the brain. A dramatic increase of delta 1/2 immunoreactivity was observed in the cerebellum between the ages of 10 and 15 d postnatal. Light and electron microscopy, respectively, demonstrated dense immunostaining in Purkinje cells and in postsynaptic densities of the adult parallel fiber-Purkinje spine synapse. The prominent delta 1/2 immunoreactivity found in the parallel fiber-Purkinje spine synapse, and the temporal correlation of the development of this synapse with the major increase in delta 1/2 immunoreactivity, suggest a major functional role for the delta subunits in cerebellar circuitry.