Presynaptic plasticity at two giant auditory synapses in normal and deaf mice

Area of Science:

• Neuroscience
• Synaptic transmission
• Auditory system plasticity

Background:

• Calyceal synapses are typically viewed as simple, high-fidelity transmission points.
• However, they can display significant activity-dependent developmental plasticity.
• This study investigates plasticity differences between two auditory calyceal synapses.

Purpose of the Study:

• To compare basal synaptic transmission and activity-dependent plasticity at the calyx of Held and endbulb of Held synapses.
• To investigate the impact of congenital deafness on these two calyceal synapses.
• To elucidate the distinct developmental plasticity capacities of these auditory synapses.

Main Methods:

• Electrophysiological recordings of excitatory postsynaptic currents (EPSCs) and miniature EPSCs (mEPSCs).
• Assessment of synaptic strength, release probability, and vesicle pool size.
• Comparison of synaptic properties in normal mice and congenitally deaf (dn/dn) mutant mice.

Main Results:

• The calyx of Held exhibits more powerful basal synaptic transmission than the endbulb of Held.
• The calyx of Held has a larger readily releasable pool (RRP) and less synaptic depression during high-frequency stimulation.
• Congenital deafness enhances endbulb synapse strength but leaves calyx synapse transmission unchanged, indicating differential plasticity.

Conclusions:

• Calyceal synapses possess greater capacity for activity-dependent developmental plasticity than previously thought.
• The calyx of Held synapse is inherently more powerful but less plastic than the endbulb of Held synapse.
• Synaptic activity levels critically influence the developmental trajectory and plasticity of different calyceal synapses in the auditory pathway.