Glutamatergic signaling at the vestibular hair cell calyx synapse

Soroush G. Sadeghi, Sonja J. Pyott, Zhou Yu, Elisabeth Glowatzki

Research output: Contribution to journalArticlepeer-review

Abstract

In the vestibular periphery a unique postsynaptic terminal, the calyx, completely covers the basolateral walls of type I hair cells and receives input from multiple ribbon synapses. To date, the functional role of this specialized synapse remains elusive. There is limited data supporting glutamatergic transmission, K+ or H+ accumulation in the synaptic cleft as mechanisms of transmission. Here the role of glutamatergic transmission at the calyx synapse is investigated. Whole-cell patch-clamp recordings from calyx endings were performed in an in vitro whole-tissue preparation of the rat vestibular crista, the sensory organ of the semicircular canals that sense head rotation. AMPA-mediated EPSCs showed an unusually wide range of decay time constants, from <5 to 500> ms. Decay time constants of EPSCs increased (or decreased) in the presence of a glutamate transporter blocker (or a competitive glutamate receptor blocker), suggesting a role for glutamate accumulation and spillover in synaptic transmission. Glutamate accumulation caused slow depolarizations of the postsynaptic membrane potentials, and thereby substantially increased calyx firing rates. Finally, antibody labelings showed that a high percentage of presynaptic ribbon release sites and postsynaptic glutamate receptors were not juxtaposed, favoring a role for spillover. These findings suggest a prominent role for glutamate spillover in integration of inputs and synaptic transmission in the vestibular periphery. We propose that similar to other brain areas, such as the cerebellum and hippocampus, glutamate spillover may play a role in gain control of calyx afferents and contribute to their high-pass properties.

Original languageEnglish (US)
Pages (from-to)14536-14550
Number of pages15
JournalJournal of Neuroscience
Volume34
Issue number44
DOIs
StatePublished - Oct 29 2014

Keywords

  • Calyx
  • Glutamate receptor
  • Hair cell
  • Spillover
  • Synaptic transmission
  • Vestibular

ASJC Scopus subject areas

  • Neuroscience(all)

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