4.3 Article

Reduced tonic inhibition in striatal output neurons from Huntington mice due to loss of astrocytic GABA release through GAT-3

期刊

FRONTIERS IN NEURAL CIRCUITS
卷 7, 期 -, 页码 -

出版社

FRONTIERS MEDIA SA
DOI: 10.3389/fncir.2013.00188

关键词

GABAergic synaptic transmission; astrocyte; GAT-3; ambient GABA; GABA(A) receptor; GABA(B) receptor; presynaptic depression; Huntington's disease

资金

  1. CHDI foundation [A-4480]
  2. German Research Council DFG [Gr986/10-1, Exc 257/1]
  3. Charite Research Funds

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The extracellular concentration of the two main neurotransmitters glutamate and GABA is low but not negligible which enables a number of tonic actions. The effects of ambient GABA vary in a region-, cell-type, and age-dependent manner and can serve as indicators of disease-related alterations. Here we explored the tonic inhibitory actions of GABA in Huntington's disease (HD). HD is a devastating neurodegenerative disorder caused by a mutation in the huntingtin gene. Whole cell patch clamp recordings from striatal output neurons (SONs) in slices from adult wild type mice and two mouse models of HD (Z_Q175_KI homozygotes or R6/2 heterozygotes) revealed an HD-related reduction of the GABA(A) receptor-mediated tonic chloride current (I-Tonic(GABA)) along with signs of reduced GABA(B) receptor-mediated presynaptic depression of synaptic GABA release. About half of I-Tonic(GABA) depended on tetrodotoxin-sensitive synaptic GABA release, but the remaining current was still lower in HD. Both in WT and HD, I-Tonic(GABA) was more prominent during the first 4 h after preparing the slices, when astrocytes but not neurons exhibited a transient depolarization. All further tests were performed within 14 h in vitro. Experiments with SNAP5114, a blocker of the astrocytic GABA transporter GAT-3, suggest that in WT but not HD GAT-3 operated in the releasing mode. Application of a transportable substrate for glutamate transporters (D-aspartate 0.11 mM) restored the non-synaptic GABA release in slices from HD mice. I-Tonic(GABA) was also rescued by applying the hyperagonist gaboxadol (0.33 mu M). The results lead to the hypothesis that lesion-induced astrocyte depolarization facilitates non-synaptic release of GABA through GAT-3. However, the capacity of depolarized astrocytes to provide GABA for tonic inhibition is strongly reduced in HD.

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