Localization of metabotropic glutamate receptor type 2 in the human brain

Metabotropic glutamate receptors are a heterogeneous family of G-protein-co upled receptors that are linked to multiple second messenger systems to reg ulate neuronal excitability and synaptic transmission. To elucidate the phy siological role of these receptors in human central nervous system function and dysfunction at the receptor protein level requires the use of selectiv e antibodies to determine the phenotype of cells expressing particular rece ptor subtypes. To this end the present study has examined the regional and cellular localization of the metabotropic glutamate type 2 receptor protein in selected human brain regions. After epitope prediction, antibodies have been generated against a short synthetic peptide corresponding to amino ac id residues located in the putative intracellular carboxy-terminus and subs equently applied to an immunohistochemical investigation. Antibodies specif ically detected the type 2 receptor in transfected mammalian cells and also recognized a major band of 98,000 mol. wt in western blots of human brain tissue membranes. At the light microscope level immunohistochemical studies have demonstrated that type 2-like immunoreactivity was widely distributed in the human brain, being characterized by the presence of a strong immuno reaction in multiple cortical regions, and in structures comprising the bas al ganglia, to include the caudate nucleus, putamen, globus pallidus, subst antia nigra and subthalamic nucleus. In the hippocampal formation, immunore activity was predominant in selective cell layers of both the dentate gyrus and cornu ammonia, the subicular complex and entorhinal cortex. In the tha lamus, multiple subnuclei showed reaction product. In the cerebellar cortex , immunoreactivity was expressed in a number of cell layers and cell types. Furthermore, using double immunofluorescence we confirmed that the type 2 receptor is a product of normal resting astrocytes in the cerebral cortex i n particular. This antibody provides a new immunological tool with the potential to evalu ate the distribution of human metabotropic glutamate receptor 2 protein in other brain regions and in human central nervous system diseases. (C) 1999 IBRO. Published by Elsevier Science Ltd.