Redundancy and multifunctionality among spinal locomotor networks.

Area of Science:

• Neuroscience
• Spinal Cord Research
• Locomotion

Background:

• c-Fos protein indicates neural activation but only captures single events.
• Targeted Recombination in Active Populations (TRAP) allows capturing two distinct neural activation patterns in vivo.
• TRAP has primarily been used for brain circuit analysis.

Purpose of the Study:

• To investigate spinal circuit activation during resting and stepping using the TRAP methodology.
• To provide novel insights into spinal network activation during motor tasks.
• To establish FosTRAP as a tool for comparing spinal interneuron engagement under various conditions.

Main Methods:

• Utilized the FosTRAP mouse model to label neuronal populations activated during specific behavioral epochs.
• Administered two distinct 30-minute stepping bouts in the same animals.
• Analyzed colabeling of c-Fos and TRAP-labeled neurons in the spinal cord.

Main Results:

• Demonstrated probabilistic recruitment of spinal neurons during repetitive stepping, with only ~20% overlap between two bouts.
• Showcased colabeling of interneurons active during both stepping and resting states.
• Revealed extensive redundancy within spinal locomotor circuits.

Conclusions:

• The FosTRAP methodology is a valuable tool for studying spinal cord circuits in vivo.
• Spinal locomotor circuits exhibit significant redundancy, allowing for flexible recruitment of neural populations.
• Variability in neural network selection enables the generation of numerous step cycles.