Activity-driven synapse elimination leads paradoxically to domination by inactive neurons

Area of Science:

• Neuroscience
• Developmental Biology
• Computational Biology

Background:

• Multiple motor axons initially innervate single neuromuscular junctions.
• Synapse elimination, a critical developmental process, refines these connections to a single axon input.
• The role of neural activity in synapse elimination is paradoxical, with conflicting experimental evidence.

Purpose of the Study:

• To resolve the paradox of activity-dependent synapse elimination.
• To develop a mathematical model explaining synapse elimination based on activity and metabolic constraints.
• To reconcile conflicting experimental findings regarding axonal activity levels and competitive advantage.

Main Methods:

• Formulation of a mathematical model for activity-mediated synapse elimination.
• Incorporation of assumptions regarding total transmitter release and metabolic constraints on synaptic support.
• Analysis of model predictions under varying activity patterns and developmental stages.

Main Results:

• The model demonstrates how synapse elimination is mediated by total transmitter release, not release frequency.
• It shows that metabolic constraints, influenced by axonal activity and neuron size, play a crucial role.
• The model explains how initially advantageous high-frequency activity can be overcome by greater synaptic efficacy at lower rates later in development.

Conclusions:

• The developed mathematical model successfully resolves the paradox of activity's role in synapse elimination.
• The model provides a unified explanation for experimental data where both active and inactive axons show competitive advantages at different stages.
• It offers insights into the origin of the size principle in motor neuron function.