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 alpha subunit variants, GlyRN (neonatal) and GlyRA (adult), have previously been identified in rodent spinal cord. Primary cultures of embyronic spinal neurons, however, express predominantly GlyRN. 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 GlyRN and GlyRA contents were elevated, as revealed by isoform-selective immunoassays and amplification of corresponding alpha 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 GlyRA 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.