Differential expression of NMDA receptor subunits between neurons containing and not containing enkephalin in the mouse embryo spinal cord

We transfected cultures of mouse spinal cord slices with the enhanced green fluorescent protein (GFP) gene driven by the promoter for preproenkephalin, using the particle-mediated gene transfer system adapted for small neurons in the superficial dorsal horn, and observations were made after 4-6 days in vitro. A considerable number of cells in the superficial dorsal horn were observed to express GFP fluorescence, reminiscent of the previously reported distribution of enkephalinergic neurons in the spinal cord. The number of GFP-expressing neurons increased in response to forskolin application. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of single neurons revealed that the N-methyl-d-aspartate (NMDA) receptor NR2B subunit is expressed more frequently in enkephalinergic neurons, and the NR2A subunit more frequently in non-enkephalinergic neurons. These observations suggest that expression of NMDA receptor subunits is controlled differentially in distinct populations of neurochemically identified neurons in the spinal cord. Biolistic particle-mediated gene transfection seems useful for identifying neuronal phenotypes in organotypic cultures of the spinal cord.