EXPRESSION OF N-METHYL-D-ASPARTATE GLUTAMATE-RECEPTOR SUBUNITS IN THEPREFRONTAL CORTEX OF THE RAT

The laminar distribution and cellular levels of expression of mRNAs en coding N-methyl-D-aspartate receptor subunits (NMDAR1, NMDAR2A-D and t he alternatively spliced isoforms of NMDAR1) were examined in prefront al cortex of rat by in situ hybridization using film and emulsion auto radiography. Film autoradiograms demonstrated a distinctive laminar di stribution of hybridization signals for each of the probes recognizing NMDAR1, NMDAR2A and NMDAR2B messenger RNA; hybridization with probes for NMDAR2C and NMDAR2D resulted in scattered signals without laminar organization. Grain counting disclosed that neurons in layer V display ed the highest and neurons in layer IV the lowest absolute number of g rains for all probes examined. Correction for cell size demonstrated s tatistically significant differences in cellular labelling density of up to 50% across neurons in different cortical layers. The cellular de nsity profiles across cortical laminae differed between probes. Hybrid ization with a probe recognizing all isoforms of NMDAR1 resulted in si gnificantly lower densities of cellular labelling in neurons of layer IV than of layers II/III, V and VI. Cellular labelling densities follo wing hybridization with probes recognizing alternatively spliced segme nts of NMDAR1 were examined. Densities were low in neurons of the uppe r cortical layers II/III and IV using probes for the messenger RNA enc oding the amino terminal insert, NMDAR1(1XX) and the second carboxy te rminal deletion, NMDAR1(XX1); hybridization with a probe for the messe nger RNA encoding the first carboxy terminal deletion, NMDAR1(X1X) res ulted in low cellular signal densities in neurons of layers IV and VIb . NMDAR2A messenger RNA expression was of relatively uniform intensity in neurons of layers II-V but significantly lower in neurons of the i nner part of layer VI. NMDAR2B expression was most dense in layer II n eurons. These data indicate that neurons in different cortical laminae express distinct N-methyl-D-aspartate receptor subunit messenger RNA phenotypes. In addition, the observed differences in density of N-meth yl-D-aspartate receptor subunit messenger RNA expression suggest that cortical laminae differ in the relative contribution of N-methyl-D-asp artate receptors to their excitatory responses. Copyright (C) 1996 IBR O. Published by Elsevier Science Ltd.