title: Differential expression of gamma-aminobutyric acid type B receptor subunit mRNAs in the developing nervous system and receptor coupling to adenylyl cyclase in embryonic neurons.
abstract: gamma-Aminobutyric acid type B receptors (GABA(B)Rs) mediate both slow inhibitory synaptic activity in the adult nervous system and motility signals for migrating embryonic cortical cells. Previous papers have described the expression of GABA(B)Rs in the adult brain, but the expression and functional significance of these gene products in the embryo are largely unknown. Here we examine GABA(B)R expression from rat embryonic day 10 (E10) to E18 compared with adult and ask whether embryonic cortical neurons contain functional GABA(B)R. GABA(B)R1 transcript levels greatly exceed GABA(B)R2 levels in the developing neural tube at E11, and olfactory bulb and striatum at E17 but equalize in most regions of adult nervous tissue, except for the glomerular and granule cell layers of the main olfactory bulb and the striatum. Consistent with expression differences, the binding affinity of GABA for GABA(B)Rs is significantly lower in adult striatum compared with cerebellum. Multiple lines of evidence from in situ hybridization, RNase protection, and real-time PCR demonstrate that GABA(B)R1a, GABA(B)R1b, GABA(B)R1h (a subunit subtype, lacking a sushi domain, that we have identified in embryonic rat brain), GABA(B)R2, and GABA(B)L transcript levels are not coordinately regulated. Despite the functional requirement for a heterodimer of GABA(B)R subunits, the expression of each subunit mRNA is under independent control during embryonic development, and, by E18, GABA(B)Rs are negatively coupled to adenylyl cyclase in neocortical neurons. The presence of embryonic GABA(B)R transcripts and protein and functional receptor coupling indicates potentially important roles for GABA(B)Rs in modulation of synaptic transmission in the developing embryonic nervous system.
authors.affiliation: Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118-2394, USA.
authors.forename: Stella C
authors.initials: SC
authors.lastname: Martin
authors.forename: Janine L
authors.initials: JL
authors.lastname: Steiger
authors.forename: María Clara
authors.initials: MC
authors.lastname: Gravielle
authors.forename: Helen R
authors.initials: HR
authors.lastname: Lyons
authors.forename: Shelley J
authors.initials: SJ
authors.lastname: Russek
authors.forename: David H
authors.initials: DH
authors.lastname: Farb
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001665:Binding Sites; D015153:Blotting, Western / Q000379:methods; D019556:COS Cells / Q000378:metabolism; D002522:Chlorocebus aethiops; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004622:Embryo, Mammalian; D018755:GABA Agonists / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D017403:In Situ Hybridization / Q000379:methods; D020128:Inhibitory Concentration 50; D008297:Male; D009420:Nervous System / Q000166:cytology* / Q000196:embryology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009943:Organophosphorus Compounds / Q000493:pharmacokinetics / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018080:Receptors, GABA-B / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D014162:Transfection; D014316:Tritium / Q000493:pharmacokinetics; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D018755:GABA Agonists; D009943:Organophosphorus Compounds; D010726:Phosphodiesterase Inhibitors; D021122:Protein Subunits; D012333:RNA, Messenger; D018080:Receptors, GABA-B; D014316:Tritium; C061388:3-aminopropylphosphinic acid; C068457:3-aminopropyl(methyl)phosphinic acid; C107353:CGP 54626; D005680:gamma-Aminobutyric Acid; D000262:Adenylyl Cyclases; D001418:Baclofen; D015056:1-Methyl-3-isobutylxanthine