Distinct forms of synaptic plasticity during ascending vs descending control of medial olivocochlear efferent neurons

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Abstract

Activity in each brain region is shaped by the convergence of ascending and descending axonal pathways, and the balance and characteristics of these determine neural output. The medial olivocochlear (MOC) efferent system is part of a reflex arc that critically controls auditory sensitivity. Multiple central pathways contact MOC neurons, raising the question of how a reflex arc could be engaged by diverse inputs. We examined functional properties of synapses onto brainstem MOC neurons from ascending (ventral cochlear nucleus, VCN), and descending (inferior colliculus, IC) sources in mice using an optogenetic approach. We found that these pathways exhibited opposing forms of short-term plasticity, with VCN input showing depression and IC input showing marked facilitation. By using a conductance clamp approach, we found that combinations of facilitating and depressing inputs enabled firing of MOC neurons over a surprisingly wide dynamic range, suggesting an essential role for descending signaling to a brainstem nucleus.

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Gabriel E Romero

Oregon Health and Science University, Portland, United States

Competing interests
The authors declare that no competing interests exist.
Laurence O Trussell

Oregon Health and Science University, Portland, United States

For correspondence
trussell@ohsu.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0003-1171-2356

Funding

National Institutes of Health (DC016226)

Gabriel E Romero

Howard Hughes Medical Institute (Gilliam Fellowship)

Gabriel E Romero

National Institutes of Health (DC004450)

Laurence O Trussell

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: Animal experimentation: All experiments were performed under the approval of the institutional animal care and use committee (IACUC) of Oregon Health and Science University, assurance #A3304-01.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.