title: 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.
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, CA 95616, USA.
authors.forename: Zhengyu
authors.initials: Z
authors.lastname: Cao
authors.forename: Susan
authors.initials: S
authors.lastname: Hulsizer
authors.forename: Flora
authors.initials: F
authors.lastname: Tassone
authors.forename: Hiu-tung
authors.initials: HT
authors.lastname: Tang
authors.forename: Randi J
authors.initials: RJ
authors.lastname: Hagerman
authors.forename: Michael A
authors.initials: MA
authors.lastname: Rogawski
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Hagerman
authors.forename: Isaac N
authors.initials: IN
authors.lastname: Pessah
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001253:Astrocytes / Q000378:metabolism; D002478:Cells, Cultured; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics* / Q000378:metabolism*; D005600:Fragile X Syndrome / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D050485:GABA Plasma Membrane Transport Proteins / Q000096:biosynthesis; D055879:Gene Knock-In Techniques; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D011280:Pregnanolone / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis; D064529:Receptor, Metabotropic Glutamate 5; D017470:Receptors, Glutamate; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors; D019680:Trinucleotide Repeat Expansion
chemical_list: D027322:Amino Acid Transport System X-AG; D001224:Aspartic Acid; D018691:Excitatory Amino Acid Antagonists; D051860:Fragile X Messenger Ribonucleoprotein 1; D050485:GABA Plasma Membrane Transport Proteins; D016202:N-Methylaspartate; D011280:Pregnanolone; D012333:RNA, Messenger; D064529:Receptor, Metabotropic Glutamate 5; D017470:Receptors, Glutamate; D018094:Receptors, Metabotropic Glutamate; C497684:Fmr1 protein, mouse; C578936:Grm5 protein, mouse; C120673:benzyloxyaspartate; C104077:metabotropic glutamate receptor type 1