Fast vesicle replenishment allows indefatigable signalling at the first auditory synapse.

Area of Science:

• Neuroscience
• Auditory system physiology
• Cell biology

Background:

• Ribbon synapses in inner hair cells are vital for auditory signal encoding.
• These synapses exhibit exceptionally high release rates and submillisecond precision.
• The mechanism for rapid vesicle replenishment at these sites remains largely unknown.

Purpose of the Study:

• To investigate the source and dynamics of vesicles involved in fast release and replenishment at inner hair cell ribbon synapses.
• To elucidate how these synapses maintain high-fidelity auditory signal transmission.

Main Methods:

• Utilized two-photon imaging in the intact mammalian cochlea.
• Focused on single synaptic release sites within inner hair cells.
• Quantified vesicle release and replenishment rates during stimulation.

Main Results:

• Observed vesicle release at a maximal initial rate of 3 vesicles per millisecond.
• Demonstrated vesicle replenishment occurring at a rate of 1.9 vesicles per millisecond.
• Identified preformed vesicles from cytoplasmic compartments as key contributors to rapid replenishment.

Conclusions:

• Preformed vesicles from cytoplasmic stores facilitate rapid neurotransmitter release and replenishment at ribbon synapses.
• This efficient vesicle resupply mechanism supports the sustained, high-precision signaling required for auditory perception.
• The findings challenge the reliance on slow, local endocytic cycling for maintaining synaptic function in the auditory system.