EXCITATORY AMINO-ACID REGULATION OF THE ENKEPHALIN PHENOTYPE IN MOUSEEMBRYONIC SPINAL-CORD CULTURES

Expression of the preproenkephalin gene in developing spinal cord-dors al root ganglia (SC-DRG) cultures was determined by Northern analysis following treatments with different agonists and antagonists of the gl utamate receptor. Cultures (10-12 days old) were treated with various concentrations (10(-7)-10(-3) M) of N-methyl-D-aspartate (NMDA), quisq ualate, kainic acid (KA), 2-amino-5-phosphonovaleric acid (APV) and 5- methyl-10,11-dihydro-H-5-dibenzo[a, d]cyclohepten-5,10-imine maleate ( MK801) either with or without blocking spontaneous electrical activity with 1 muM tetrodotoxin (TTX). In electrically active cultures, treat ments with NMDA and KA increased preproenkephalin transcripts (mRNA(pp ENK)), showing maximum effects at 1 muM (4-fold and 2-fold, respective ly), while treatments with quisqualate and MK801 caused concentration- dependent down-regulation in mRNA(ppENK). The most effective concentra tions of NMDA (1 muM) and quisqualate (10 muM) altered mRNA(ppENK) lev els within 4 h of treatment and peaked after 24 h for NMDA and 48 h fo r quisqualate treatment. Co-treatment with APV completely blocked the NMDA-induced rise of mRNA(ppENK). During electrical blockade, none of the concentrations of NMDA tested showed any effect on enkephalin expr ession, neither could NMDA pre-treatment prevent the TTX-induced down- regulation of mRNA(ppENK). Our results indicate that the activity-depe ndent establishment of the enkephalin phenotype is modulated through t he selective activation of the NMDA-glutamate receptor.