Expression of NR1, NR2A-D, and NR3 Subunits of the NMDA Receptor in the Cerebral Cortex and Olfactory Bulb of Adult Rat

Quantitative reverse transcriptase - polymerase chain reaction was used to analyze the relative expressions of NR1, NR2A, NR2B, NR2C, NR2D, and NR3 subunits of the NMDA receptor in the piriform, entorhinal, visual, and motor cortices as well as in the olfactory bulb of adult rat. The analysis detected clear differences in the relative proportions of the NMDA receptor subunits between the five forebrain regions examined. These differences were particularly striking when the piriform and motor cortices were compared. In the piriform cortex, NR1 was the predominant transcript. The expression of NR2A was only slightly higher than half of that of NR1. NR2B was expressed even at lower levels ( approximately 30% of NR1). NR2C and NR3 were expressed at levels which were approximately 15% of those of NR1. NR2D had the lowest levels of expression ( approximately 3% of NR1). In contrast, NR2B was the predominant transcript in the motor cortical region, where it was expressed at the levels close to 135% of those of NR1 message. NR2A had the levels of expression of approximately 50% of those of NR1. The NR2C expression was close to 25% that of NR1, and the NR2D and NR3 transcripts were totally absent from this cortical area. These findings suggest a significant regional variability of the NMDA receptors in the adult rat forebrain.