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Keywords:

  • Chronic ethanol;
  • Alcohol dependence;
  • GABAA receptor;
  • α4 subunit;
  • Hippocampus;
  • In situ hybridization

Abstract

  1. Top of page
  2. Abstract

Abstract: Chronic administration of ethanol to rats on an intermittent regimen, for 60 repeated intoxicating doses and repeated withdrawal episodes, results in a long-lasting kindling phenomenon. This involves an increasing severity of withdrawal, including a reduced threshold to seizures produced by the GABAA antagonist, pentylenetetrazol. We have shown previously that muscimol-evoked 36Cl efflux and paired-pulse inhibition (involving GABAA-mediated recurrent inhibition) were decreased persistently in the CA1 region of hippocampal slices from chronic intermittent ethanol (CIE)-treated rats. We now report elevated levels of mRNA in forebrain for the α4 subunit of the GABAA receptor (GABAR), considered to be a constituent of pharmacologically and physiologically novel subtypes of GABARs. Using in situ hybridization with digoxigenin-labeled RNA probes, we show that at 2 days withdrawal, 60-dose CIE leads to a significant 30% increase in α4 subunit mRNA levels in the dentate gyrus, 46% increase in the CA3, and 26% increase in the CA1 regions. In contrast, there was no significant change in the mRNAs for the α5 subunit or glutamic acid decarboxylase 67 in the same regions. This study suggests that GABAR subunit-selective alterations occur after CIE treatment, possibly resulting in the alteration of the subunit composition of GABARs, with presumably altered physiological functions. This plasticity of GABARs may contribute to the increased withdrawal severity, reduced hippocampal inhibition, and increased seizure susceptibility of this animal model of human alcohol dependence.

Abbreviations used: CIE, chronic intermittent ethanol; DIG, digoxigenin; DZ-IS, diazepam-insensitive; GABAR, GABAA receptor; GAD, l-glutamic acid decarboxylase; PBS, phosphate-buffered saline; SSC, saline-sodium citrate buffer.