Modulation by NMDA Receptor Antagonists of Glycine Receptor Isoform Expression in Cultured Spinal Cord Neurons

Two developmentally regulated isoforms of the inhibitory glycine receptor harbouring different α subunit variants, GlyR_N (neonatal) and GlyR_A (adult), have previously been identified in rodent spinal cord. Primary cultures of embyronic spinal neurons, however, express predominantly GlyR_N. Here, N-methyl-d-aspartate (NMDA) receptor antagonists were found to significantly increase glycine receptor levels in mouse spinal cord cultures. In the presence of 2-amino-5-phosphonovalerate or MK-801 (dizocilpine), both GlyR_N and GlyR_A contents were elevated, as revealed by isoform-selective immunoassays and amplification of corresponding α subunit transcripts by the polymerase chain reaction. This effect of NMDA receptor antagonists was restricted to a ‘sensitive’ period within the second week after plating. Apparently, NMDA receptor-mediated glutamate neurotoxicity prevented GlyR_A accumulation under standard culture conditions. Our data indicate that neuronal maturation in cell culture depends on conditions which minimize cell death resulting from glutamate release into the culture medium.