Clustered burst firing in FMR1 premutation hippocampal neurons: amelioration with allopregnanolone

Abstract

Premutation CGG repeat expansions (55-200 CGG repeats; preCGG) within the fragile X mental retardation 1 (FMR1) gene cause fragile X-associated tremor/ataxia syndrome (FXTAS). Defects in neuronal morphology and migration have been described in a preCGG mouse model. Mouse preCGG hippocampal neurons (170 CGG repeats) grown in vitro develop abnormal networks of clustered burst (CB) firing, as assessed by multielectrode array recordings and clustered patterns of spontaneous Ca(2+) oscillations, neither typical of wild-type (WT) neurons. PreCGG neurons have reduced expression of vesicular GABA and glutamate (Glu) transporters (VGAT and VGLUT1, respectively), and preCGG hippocampal astrocytes display a rightward shift on Glu uptake kinetics, compared with WT. These alterations in preCGG astrocytes and neurons are associated with 4- to 8-fold elevated Fmr1 mRNA and occur despite consistent expression of fragile X mental retardation protein levels at ∼50% of WT levels. Abnormal patterns of activity observed in preCGG neurons are pharmacologically mimicked in WT neurons by addition of Glu or the mGluR1/5 agonist, dihydroxyphenylglycine, to the medium, or by inhibition of astrocytic Glu uptake with dl-threo-β-benzyloxyaspartic acid, but not by the ionotropic Glu receptor agonists, α-2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl) propanoic acid or N-methyl-d-aspartic acid. The mGluR1 (7-(hydroxyimino)cyclopropa [b]chromen-1a-carboxylate ethyl ester) or mGluR5 (2-methyl-6-(phenylethynyl)pyridine hydrochloride) antagonists reversed CB firing. Importantly, the acute addition of the neurosteroid allopregnanolone mitigated functional impairments observed in preCGG neurons in a reversible manner. These results demonstrate abnormal mGluR1/5 signaling in preCGG neurons, which is ameliorated by mGluR1/5 antagonists or augmentation of GABA(A) receptor signaling, and identify allopregnanolone as a candidate therapeutic lead.

Inhibition of microRNA 128 promotes excitability of cultured cortical neuronal networks

“…The MFR observed for the control populations was within range of published values using MEA systems (Eytan and Marom 2006;Cao et al 2012;Bateup et al 2013;Colombi et al 2013;Lignani et al 2013). We found that inhibition of miR-128 resulted in increased MFR, increased burst rate, and an increase in the number of network events in both immature and mature cultures.…”

ERP abnormalities elicited by word repetition in fragile X-associated tremor/ataxia syndrome (FXTAS) and amnestic MCI

“…[45,46] Mouse models of the fragile X premutation have found reduced induction of long-term potentiation (LTP) and increases in both NMDA and mGluR-mediated LTD.[47] These effects are large 10-20 minutes post-conditioning, and then became smaller and insignificant by 40-50 minutes. [47] Hippocampal neurons from mice with the fragile X premutation show a clustered burst firing pattern and imbalanced excitatory–inhibitory (i.e., glutamate-GABA) neurotransmission [48]. Further studies with cognitive ERP/EEG and brain-imaging modalities are needed to determine the macroscopic effects of the synaptic dysfunction in both FXTAS and AD, and elucidate their impact on memory, language and other cognitive processes.…”

Nanomolar Bifenthrin Alters Synchronous Ca2+Oscillations and Cortical Neuron Development Independent of Sodium Channel Activity

“…In FMR1 gene knockout mouse model, enhanced mGluR5 signaling has been demonstrated and contributes to long-term synaptic depression during synaptic transmission. Such disturbances in mGluR5 signaling are thought to elicit cognitive as well as syndromic features of fragile X syndrome (Huber et al, 2002;Bear et al, 2004;Dolen and Bear, 2008), and FMR1 premutation (Chen et al, 2010;Cao et al, 2012b;Liu et al, 2012). Our in vitro observation that nanomolar bifenthrin alters neuronal Ca 21 dynamics and mGluR5 signaling activity with consequential changes in neurite outgrowth provides evidence for a new paradigm in understanding how certain pyrethroids might influence health outcomes that involve abnormal neuronal network development associated with developmental disorders.…”

“…The sample preparation for Western blot was performed as described previously (Cao et al, 2012b). An equal amount of sample protein (20 mg) was loaded onto the wells of 10% SDS-PAGE gels and transferred to a nitrocellulose membrane by electroblotting.…”