Induction of Activity-Dependent Plasticity at Auditory Nerve Synapses

Area of Science:

• Neuroscience
• Auditory System Research
• Synaptic Plasticity

Background:

• Nontraumatic noise exposure causes lasting changes in auditory nerve synapses, potentially affecting hearing.
• The precise mechanisms driving these synaptic alterations remain largely unknown.

Purpose of the Study:

• To elucidate the molecular and cellular mechanisms underlying activity-induced synaptic changes in the auditory nerve.
• To investigate the role of nitric oxide (NO) and glutamate receptors in mediating these long-lasting synaptic modifications.

Main Methods:

• Utilized high potassium and optogenetic stimulation in acute mouse cochlear nucleus slices to mimic auditory nerve activity.
• Performed voltage-clamp recordings on bushy cells to measure synaptic function (EPSC amplitude, quantal size, release probability).
• Employed pharmacological agents, including NO synthase blockers, protein kinase A inhibitors, and glutamate receptor antagonists.

Main Results:

• High potassium treatment reduced EPSC amplitude, quantal size, and release probability (Pr), effects blocked by NO synthase and protein kinase A inhibitors.
• Optogenetic activation of auditory nerve fibers decreased EPSC amplitude and Pr, an effect prevented by glutamate receptor antagonists and NO synthase inhibitors.
• Nitric oxide (NO) was identified as a key mediator, with NO donors mimicking the effects of high potassium on synaptic function.

Conclusions:

• Auditory nerve activity, acting through postsynaptic AMPA and NMDA receptors, triggers NO release.
• This NO acts retrogradely to induce long-lasting functional changes in auditory nerve synapses.
• These findings offer insights into mechanisms underlying hearing changes due to noise exposure and potential therapeutic targets.