Corticospinal tract development and spinal cord innervation differ between cervical and lumbar targets

Area of Science:

• Neuroscience
• Developmental Biology
• Motor Control

Background:

• The corticospinal tract is crucial for voluntary movement.
• Its precise organization and developmental trajectory remain incompletely understood.

Purpose of the Study:

• To map the cortical areas projecting to the C7 spinal cord segment, which controls forelimb movement.
• To investigate developmental changes in corticospinal projections and their synaptic connections.

Main Methods:

• Retrograde tracer injections into the C7 spinal cord segment in mice.
• Optogenetic stimulation of corticospinal axons and whole-cell recordings.
• Axon and presynaptic structure labeling using electroporation.

Main Results:

• Neurons from a broad cortical region, including hindlimb areas, project to C7.
• Axon density decreases with age due to branch elimination.
• Developing corticospinal axons form synaptic connections in juveniles, indicating significant circuit reorganization.

Conclusions:

• Cortical control of forelimb movement is more widespread than traditionally thought.
• Significant developmental differences exist in the cortical control of forelimb versus hindlimb movements in rodents.