MOLECULAR CHARACTERIZATION AND LOCALIZATION OF HUMAN METABOTROPIC GLUTAMATE-RECEPTOR TYPE-3

A human brain cDNA library was screened using amplified human metabotr opic glutamate receptor (mGluR) cDNA sequences as probes. The resultin g clones included one containing the complete coding sequence of mGluR 3. This sequence has 90% DNA sequence identity with rat mGluR3 and the predicted protein sequence has 97% identity. The mGluR3 cDNA was tran sfected in Chinese hamster ovary (CHO) cells. Stimulation of the expre ssed receptor by (2S,3S,4S)-alpha-(carboxycyclopropyl) glycine (L-CCG- I) resulted in a reduction of forskolin-stimulated cyclic AMP (cAMP) w ith EC(50) values of 0.15-0.3 mu M. A specific probe from the human mG luR3 clone was used to hybridise to Northern blots of mRNA from variou s human tissues and different brain regions. The mGluR3 mRNA is brain- specific, and is expressed in all the brain regions represented on the blot. In-situ hybridization studies on human brain sections confirmed this widespread distribution with expression in neurones in the cereb ral cortex, caudate-putamen, thalamus and cerebellum.