Abstract
Drinking alcohol is associated with the disturbance of normal sleep rhythms, and insomnia is a major factor in alcoholic relapse. The thalamus is a brain structure that plays a pivotal role in sleep regulation and rhythmicity. A number of studies have implicated GABAA receptors (GABAA-Rs) in the anxiolytic, amnestic, sedative, and anesthetic effects of ethanol. In the present study, we examined the effects of ethanol on both synaptic and extrasynaptic GABAA-Rs of relay neurons in the thalamus. We found that ethanol (≥50 mM) elicits a sustained current in thalamocortical relay neurons from the mouse ventrobasal thalamus, and this current is associated with a decrease in neuronal excitability and firing rate in response to depolarization. The steady current induced by ethanol was totally abolished by gabazine and was absent in relay neurons from GABAA-R α4 subunit knockout mice, indicating that the effect of ethanol is to enhance tonic GABA-mediated inhibition. Ethanol (50 mM) enhanced the amplitude of tonic inhibition by nearly 50%. On the other hand, ethanol had no effect on spontaneous or evoked inhibitory postsynaptic currents (IPSCs) at 50 mM but did prolong IPSCs at 100 mM. Ethanol had no effect on the paired-pulse depression ratio, suggesting that the release of GABA from presynaptic terminals is insensitive to ethanol. We conclude that ethanol, at moderate (50 mM) but not low (10 mM) concentrations, can inhibit thalamocortical relay neurons and that this occurs mainly via the actions of ethanol at extrasynaptic GABAA-Rs containing GABAA-R α4 subunits.
Footnotes
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The work was supported by National Institutes of Health Grants AA 16393 (to N.L.H.) and AA 13004 and GM 47818 (to G.E.H.).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.139303.
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ABBREVIATIONS: GABAA-R(s), GABAA receptor(s); IPSC, inhibitory postsynaptic current; AP, action potential; CNS, central nervous system; VB, ventrobasal thalamic nucleus.
- Received March 21, 2008.
- Accepted May 12, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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