Expression of GABA receptor subunits in the hippocampus and thalamus after experimental traumatic brain injury

Traumatic brain injury is a major cause of death and disability worldwide and often associated with post-traumatic epilepsy. We recently demonstrated that TBI induces acquired GABA(A) receptors channelopathy that associates with hyperexcitability in granule cell layer (GCL). We now assessed the expression of GABA(A) and GABA(B) receptor subunit mRNAs between 6 h and 6 months post-TBI in the hippocampus and thalamus. The expression of major GABA(A) receptor subunit mRNAs (alpha 1, alpha 2, alpha 5, beta 2, beta 3, gamma 2 and delta) was, often bilaterally, down-regulated in the GCL and in the CA3 pyramidal cells. Instead, expression of alpha 4 (GCL, CA3, CA1), alpha 5 (CA1) and gamma 2 (GCL, CA3, CA1) mRNA was up-regulated after 10 d and/or 4 months. Many of these changes were reversible. In the thalamus, we found decreases in alpha 1, alpha 4, beta 2, gamma 2 and delta mRNAs in the laterodorsal thalamus and in the area combining the posterior thalamic nuclear group, ventroposterolateral and ventroposteromedial complex at 6 h to 4 months post-TBI. Unlike in the hippocampus, thalamic subunit down-regulations were irreversible and limited to the ipsilateral side. However, contralaterally there was up-regulation of the subunits delta and alpha 4 6 h and 4 months after TBI, respectively. PCR array analysis suggested a mild long-lasting GABA(A) receptor channelopathy in the GCL and thalamus after TBI. Whereas TBI induces transient changes in the expression of GABAA receptor subunits in the hippocampus (presumably representing compensatory mechanisms), alterations of GABA(A) receptor subunit mRNAs in the thalamus are long-lasting and related to degeneration of receptor-containing neurons in thalamo-cortical relay nuclei. This article is part of the Special Issue entitled 'GABAergic Signaling in Health and Disease'. (C) 2014 The Authors. Published by Elsevier Ltd.