Targeted disruption of NMDA receptor 1 gene abolishes NMDA response and results in neonatal death

In vitro studies have suggested that the NMDA receptor consists of an essential subunit, NR1, and various modulatory NR2 subunits. To test this hypothesis directly in vivo, we generated mice carrying a disrupted NR I allele. NMDA-inducible increases in intracellular calcium and membrane currents were abolished in neurons from homozygous null mutants (NR1^-/-). Thus, NR1 has a unique role, which cannot be substituted by any other subunit, in determining the activity of the endogenous NMDA receptor. A concomitant reduction in levels of NR2B but not NR2A occurred in NR1^-/- mice, demonstrating that there is an interdependence of subunit expression. NR1^-/- mice died 8-15 hr after birth, indicating a vital neonatal function for the NMDA receptor. Although the NMDA receptor has been implicated in several aspects of neurodevelopment, overall neuroanatomy of NR1^-/- mice appeared normal. Pathological evidence suggested that respiratory failure was the ultimate cause of death.