Modulation of GABAergic and glutamatergic transmission by ethanol in the developing neocortex: an in vitro test of the excessive inhibition hypothesis of fetal alcohol spectrum disorder.
Exposure to ethanol during development triggers neuronal cell death and this is thought to play a central role in the pathophysiology of fetal alcohol spectrum disorder (FASD). Studies suggest that ethanol-induced neurodegeneration during the period of synaptogenesis results from widespread potentiation of GABA(A) receptors and inhibition of NMDA receptors throughout the brain, with neocortical layer II being particularly sensitive. Here, we tested whether ethanol modulates the function of these receptors during this developmental period using patch-clamp electrophysiological and Ca(2+) imaging techniques in acute slices from postnatal day 7-9 rats. We focused on pyramidal neurons in layer II of the parietal cortex (with layer III as a control). Ethanol (70mM) increased spontaneous action potential-dependent GABA release in layer II (but not layer III) neurons without affecting postsynaptic GABA(A) receptors. Protein and mRNA expression for both the Cl(-) importer, NKCC1, and the Cl(-) exporter, KCC2, were detected in layer II/III neurons. Perforated-patch experiments demonstrated that E(Cl)((-)) is shifted to the right of E(m); activation of GABA(A) receptors with muscimol depolarized E(m), decreased action potential firing, and minimally increased [Ca(2+)](i). However, the ethanol-induced increase of GABAergic transmission did not affect neuronal excitability. Ethanol had no effect on currents exogenously evoked by NMDA or AMPA receptor-mediated spontaneous excitatory postsynaptic currents. Acute application of ethanol in the absence of receptor antagonists minimally increased [Ca(2+)](i). These findings are inconsistent with the excessive inhibition model of ethanol-induced neurodegeneration, supporting the view that ethanol damages developing neurons via more complex mechanisms that vary among specific neuronal populations.
Sanderson
Jennifer L
JL
Department of Neurosciences, University of New Mexico, Health Sciences Center, BMSB 145, MSC08 4740, Albuquerque, NM 87131-0001, USA.
Donald Partridge
L
L
Valenzuela
C Fernando
CF
D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D002118:Calcium / Q000378:metabolism; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D000431:Ethanol / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists; D005260:Female; D018755:GABA Agonists / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D019579:Neocortex / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D017966:Pyramidal Cells / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2; D027981:Symporters / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D000096922:K Cl- Cotransporters
D002118:Calcium; D002492:Central Nervous System Depressants; D016291:Dizocilpine Maleate; D000431:Ethanol; D018691:Excitatory Amino Acid Antagonists; D018755:GABA Agonists; D018698:Glutamic Acid; D009118:Muscimol; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D027981:Symporters; D005680:gamma-Aminobutyric Acid; D000096922:K Cl- Cotransporters; C578879:Slc12a2 protein, rat