SURVIVAL AND SYNAPTOGENESIS OF HIPPOCAMPAL-NEURONS WITHOUT NMDA RECEPTOR FUNCTION IN CULTURE

Physiological and morphological properties of cultured hippocampal neu rons were measured to investigate whether NMDA receptors play a role i n survival and differentiation. Neurons dissociated from mouse embryos with different NMDAR1 genotypes were grown in culture. Electrophysiol ogical analysis verified the absence of NMDA receptor-mediated current s in neurons taken from homozygous mutant (NR1 -/-) embryos. The numbe r of surviving hippocampal neurons was 2.5-fold higher in cultures fro m the NR1 -/- embryos compared with wild type (NR1 +/+) and heterozygo us (NR1 +/-) controls. Despite the lack of NMDA receptor function, NR1 -/- neurons formed synapsin I-positive presynaptic boutons associated with MAP2ab-positive dendrites in culture. Confocal microscopic analy sis of Dil labelled neurons confirmed the presence of dendritic spines on NR1 -/- neurons with 80% of the density found in NR1 +/+ neurons. These results suggest that the NMDA receptor has little effect on gene ral features of neuronal differentiation. In contrast, there is clear effect on neuronal survival. This finding establishes neuron number in standard culture conditions as a measure of NMDA receptor activity.