Anatomy and activity patterns in a multifunctional motor neuron and its surrounding circuits

Area of Science:

• Neuroscience
• Computational Neuroscience
• Motor Control

Background:

• The dorsal excitor motor neuron (DE-3) in the medicinal leech exhibits distinct functional roles in various behaviors, including swimming, crawling, and escape.
• Understanding how a single motor neuron dynamically switches roles without altering its anatomical structure is a key question in motor control.

Purpose of the Study:

• To investigate the relationship between the circuit anatomy and the activity patterns of the DE-3 neuron across different behaviors.
• To analyze the distribution and functional clustering of DE-3's input synapses during swimming and crawling.

Main Methods:

• Voltage-sensitive dye imaging was used to record neural activity from DE-3 and other neurons during fictive swimming, crawling, and escape behaviors.
• Serial block-face electron microscopy was employed to reconstruct the detailed anatomical processes of DE-3 and its presynaptic partners.

Main Results:

• Input synapses onto DE-3 were found to be widely distributed across its neuronal branches.
• Functional clusters of synapses differed significantly between swimming and crawling behaviors, despite the overall distribution remaining broad.

Conclusions:

• The DE-3 neuron's ability to dynamically switch roles is supported by a combination of widespread synaptic inputs and behavior-specific functional organization of these inputs.
• Circuit anatomy, specifically the spatial and functional arrangement of synapses, plays a crucial role in enabling neuronal flexibility and diverse behavioral outputs.