Work

Deficits in the activity of presynaptic γ-aminobutyric acid type B receptors contribute to altered neuronal excitability in fragile X syndrome

Year: 2017

Type: article

Abstract: The behavioral and anatomical deficits seen in fragile X syndrome (FXS) are widely believed to result from imbalances in the relative strengths of excitatory and inhibitory neurotransmission. Although modified neuronal excitability is thought to be of significance, the contribution that alterations in GABAergic inhibition play in the pathophysiology of FXS are ill defined. Slow sustained neuronal inhibition is mediated by γ-aminobutyric acid type B (GABA B ) receptors, which are heterodimeric G-protein-coupled receptors constructed from R1a and R2 or R1b and R2 subunits. Via the activation of G i/o , they limit cAMP accumulation, diminish neurotransmitter release, and induce neuronal hyperpolarization. Here we reveal that selective deficits in R1a subunit expression are seen in Fmr1 knock-out mice (KO) mice, a widely used animal model of FXS, but the levels of the respective mRNAs were unaffected. Similar trends of R1a expression were seen in a subset of FXS patients. GABA B receptors (GABA B Rs) exert powerful pre- and postsynaptic inhibitory effects on neurotransmission. R1a-containing GABA B Rs are believed to mediate presynaptic inhibition in principal neurons. In accordance with this result, deficits in the ability of GABA B Rs to suppress glutamate release were seen in Fmr1-KO mice. In contrast, the ability of GABA B Rs to suppress GABA release and induce postsynaptic hyperpolarization was unaffected. Significantly, this deficit contributes to the pathophysiology of FXS as the GABA B R agonist ( R )-baclofen rescued the imbalances between excitatory and inhibitory neurotransmission evident in Fmr1-KO mice. Collectively, our results provided evidence that selective deficits in the activity of presynaptic GABA B Rs contribute to the pathophysiology of FXS.

Source: Journal of Biological Chemistry

DOI: 10.1074/jbc.m116.772541