# Shedding light on balance: Interrogating individual synapses within vestibular epithelia

> **NIH NIH R21** · UNIVERSITY OF CALIFORNIA LOS ANGELES · 2024 · $195,000

## Abstract

Project Summary
 The present application proposes a developmental research plan to investigate the structure-function
relationship of individual presynaptic complexes in mammalian vestibular hair cells. These complexes
incorporate synaptic ribbons that can exhibit broad architectural heterogeneity, the functional significance of
which is not known. The distribution of presynaptic architectures in the primary hair cell phenotypes (i.e. types I
and II) within vestibular epithelia, and the unique dendritic specialization known as the calyx (encapsulating type
I hair cells), render traditional methods of investigating synaptic function inappropriate for elucidating the
functional characteristics of individual synaptic sites. Recent advances in the development of optical biosensors
and viral transduction strategies provide the foundation for novel capabilities to detect and quantify
neurotransmitter release at individual synapses. iGluSnFR is a genetically encoded, membrane bound
glutamate sensor. When expressed at the postsynaptic membrane, it emits a fluorescent signal proportional to
glutamate release. Recent key investigations demonstrated that when packaged with an AAV9 capsid and a
synapsin promoter, inner ear afferent neurons are transduced and iGluSnFR is expressed. This strategy directs
the sensor to the appropriate postsynaptic targets for measuring glutamate release from individual hair cell
synapses. When coupled with strategies for post-recording elucidation of synaptic ribbons an association
between glutamate release and synapse structure can be made. The project includes three Aims to: 1) optimize
transduction in vestibular afferent neurons; 2) develop and optimize recording strategies to capture the time-
resolved glutamate release from individual synaptic sites; and 3) evaluate the methods in a mouse model for
which presynaptic function in type I hair cells is drastically attenuated. Immunohistochemical processing
following optical recording will enable the direct association of immunolabeled ribbons with the recording sites,
for which ribbon volume provides a proxy of its architecture. The development of these methods provides the
foundation future studies of pathologic conditions whose etiologies are proposed to involve synaptopathies. This
investigation will enable future investigations of synaptic function in normal and pathologic conditions, and
provide a platform for the rigorous evaluation of novel treatments of inner ear dysfunction.

## Key facts

- **NIH application ID:** 10754570
- **Project number:** 5R21DC020581-02
- **Recipient organization:** UNIVERSITY OF CALIFORNIA LOS ANGELES
- **Principal Investigator:** LARRY F HOFFMAN
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $195,000
- **Award type:** 5
- **Project period:** 2023-02-01 → 2026-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10754570

## Citation

> US National Institutes of Health, RePORTER application 10754570, Shedding light on balance: Interrogating individual synapses within vestibular epithelia (5R21DC020581-02). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10754570. Licensed CC0.

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