What they found
TL;DR (qwen3.6:35b): iLOC neurons become progressively more excitable during development and aging due to specific shifts in potassium channel currents, independent of hair cell health. Genetic models that cause efferent rewiring do not replicate the biophysical changes seen in natural aging, indicating these processes are distinct.
Intrinsic lateral olivocochlear (iLOC) neurons provide vital brainstem efferent feedback to the cochlea in order to modulate hearing sensitivity through synapses onto type-I spiral ganglion neurons. During ageing or mutations affecting hair cell transduction in mice, efferent neurons rewire to form direct axo-somatic synapses onto inner hair cells (IHCs), recapitulating a synaptic configuration typically only restricted to the immature cochlea. Whether this rewiring reflects a compensatory mechanism or some form of attempted repair, or how iLOC biophysics change throughout ageing and this rewiring process, is not known. We utilised whole-cell patch-clamp electrophysiology to investigate iLOC activity and their underlying biophysics across the wild-type mouse lifespan. We show that iLOC neurons undergo a progressive increase in excitability with post-natal development and ageing, producing more spikes for a given stimulus. This intrinsic excitability shift was driven by the developmental decline in the A-type Kv4 mediated potassium current and increase in Kv2 mediated current. In ageing animals, and distinct from post-natal development, further increased firing rates were supported by an increased size of the fast-activating Kv3 current. Spontaneous bursting activity remained present in ageing iLOC neurons, and no reversion to an immature biophysics profile was evident. Interestingly, despite robustly eliciting efferent rewiring of IHCs, an accelerated ageing-like re-innervation genetic model did not recreate the biophysical changes in the iLOC neurons that reflected the ageing system. This work reveals distinct processes occurring within the iLOC feedback system, and shows that age-related enhancements of SGN resting activity are not triggered by deficits in IHC transduction.
How this applies to our program
This study clarifies that age-related changes in efferent neuron excitability are intrinsic and not caused by hair cell dysfunction, which is critical for interpreting STRC/DFNB16 models where hair cells are compromised. It suggests that observed rewiring in mutant mice may be a structural adaptation rather than a direct result of altered iLOC biophysics driven by hearing loss.
Key numbers
- A-type Kv4 current declines during development
- Kv2 mediated current increases during development
- Fast-activating Kv3 current size increases in aging animals
Links
- biorxiv_id: https://www.biorxiv.org/content/10.64898/2026.07.02.736013
- DOI: https://doi.org/10.64898/2026.07.02.736013
Connections
[source]auto-indexed 2026-07-04 by strc-lit-watch