Balanced synapse-to-synapse short-term plasticity ensures constant transmitter release

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Motor Neuron Function

Background:

• Synaptic strength exhibits variability between individual synapses.
• Short-term plasticity (STP) describes rapid changes in synaptic transmission.
• Understanding synaptic variability is crucial for neural circuit function.

Purpose of the Study:

• To investigate the heterogeneity of basal synaptic strength and short-term plasticity at Drosophila glutamatergic motor neuron synapses.
• To determine how synaptic strength and plasticity vary across individual synapses within a single motor neuron terminal.
• To explore the mechanisms maintaining overall synaptic strength distribution despite individual synapse variability.

Main Methods:

• Utilized optical quantal analysis for high-resolution measurement of synaptic transmission.
• Examined Drosophila glutamatergic motor neuron synapses.
• Analyzed basal synaptic strength and short-term plasticity (facilitation and depression) at the single-synapse level.

Main Results:

• Observed significant heterogeneity in basal synaptic strength and short-term plasticity among individual synapses, even those from the same motor neuron.
• Found that facilitating and depressing synapses, as well as strong and weak synapses, were randomly distributed within the nerve terminal.
• Demonstrated that despite heterogeneous synaptic properties, the overall distribution of synaptic strength remained constant across the nerve terminal.
• Identified a balance between facilitating and depressing synapses, their degree of plasticity, and basal synaptic weight as key factors for maintaining this constancy.

Conclusions:

• Synaptic strength and short-term plasticity are highly variable at the individual synapse level in Drosophila motor neurons.
• A dynamic balance between synaptic facilitation and depression, alongside their respective strengths, ensures a stable overall synaptic strength distribution.
• This constancy in transmitter release contributes to the robustness of neural circuits under varying behavioral demands.