Cited by 58Genetics and Neurodevelopmental DisordersHearing, Cochlea, Tinnitus, GeneticsNeuroscience and Neuropharmacology Research

Enhanced excitatory connectivity and disturbed sound processing in the auditory brainstem of fragile X mice

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Garcia-Pino, Elisabet, Gessele, Nikodemus, Koch, Ursula·2017·The Journal of Neuroscience

Abstract

Hypersensitivity to sounds is one of the prevalent symptoms in individuals with Fragile X syndrome (FXS). It manifests behaviorally early during development and is often used as a landmark for treatment efficacy. However, the physiological mechanisms and circuit-level alterations underlying this aberrant behavior remain poorly understood. Using the mouse model of FXS (Fmr1 KO), we demonstrate that functional maturation of auditory brainstem synapses is impaired in FXS. Fmr1 KO mice showed a greatly enhanced excitatory synaptic input strength in neurons of the lateral superior olive (LSO), a prominent auditory brainstem nucleus, which integrates ipsilateral excitation and contralateral inhibition to compute interaural level differences. Conversely, the glycinergic, inhibitory input properties remained unaffected. The enhanced excitation was the result of an increased number of cochlear nucleus fibers converging onto one LSO neuron, without changing individual synapse properties. Concomitantly, immunolabeling of excitatory ending markers revealed an increase in the immunolabeled area, supporting abnormally elevated excitatory input numbers. Intrinsic firing properties were only slightly enhanced. In line with the disturbed development of LSO circuitry, auditory processing was also affected in adult Fmr1 KO mice as shown with single-unit recordings of LSO neurons. These processing deficits manifested as an increase in firing rate, a broadening of the frequency response area, and a shift in the interaural level difference function of LSO neurons. Our results suggest that this aberrant synaptic development of auditory brainstem circuits might be a major underlying cause of the auditory processing deficits in FXS. SIGNIFICANCE STATEMENT Fragile X Syndrome (FXS) is the most common inheritable form of intellectual impairment, including autism. A core symptom of FXS is extreme sensitivity to loud sounds. This is one reason why individuals with FXS tend to avoid social interactions, contributing to their isolation. Here, a mouse model of FXS was used to investigate the auditory brainstem where basic sound information is first processed. Loss of the Fragile X mental retardation protein leads to excessive excitatory compared with inhibitory inputs in neurons extracting information about sound levels. Functionally, this elevated excitation results in increased firing rates, and abnormal coding of frequency and binaural sound localization cues. Imbalanced early-stage sound level processing could partially explain the auditory processing deficits in FXS.

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  1. Case DT, Zhao X, Gillespie DC (2011b) Functional refinement in the pro- jection from ventral cochlear nucleus to lateral superior olive precedes hearing onset in rat. PLoS One 6:e20756. CrossRef · DOI

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Authors
Garcia-Pino, E., Gessele, N., & Koch, U.
Affiliations
  • Freie Universität Berlin (DE)
  • NeuroCure Cluster of Excellence (DE)
Venue
The Journal of Neuroscience
Published
2017-07-03
Volume
37
Issue
31
Pages
7403-7419
ISSN
  • 0270-6474 (ISSN-L)
  • 1529-2401
OpenAlex
W2725607499
Cited by
58
References
82
Citations by year
2026: 3 · 2025: 9 · 2024: 2 · 2023: 3 · 2022: 10 · 2021: 6 · 2020: 5 · 2019: 10 · 2018: 7 · 2017: 3
FWCI
4.54
Type
journal article
Language
en
Open access
Locations
  • Journal of Neuroscience (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • European Commission
  • Deutsche Forschungsgemeinschaft (SPP 1608, SFB 665)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Genetics and Neurodevelopmental Disorders
  • Life Sciences › Neuroscience › Sensory Systems › Hearing, Cochlea, Tinnitus, Genetics
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neuropharmacology Research
Keywords
fragile X syndrome, Fmr1 knockout mice, auditory brainstem, lateral superior olive, excitatory synaptic input, interaural level difference, binaural localization, cochlear nucleus, glycinergic inhibition, auditory processing deficits, synaptic development, FMRP
MeSH terms
Animals, Auditory Cortex, Auditory Pathways, Auditory Perception, Brain Stem, Female, Fragile X Syndrome, Hearing Disorders, Male, Evoked Potentials, Auditory, Brain Stem, Mice, Knockout, Excitatory Postsynaptic Potentials, Mice, Fragile X Mental Retardation Protein, Fragile X Messenger Ribonucleoprotein 1

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