Axonal projections of Renshaw cells in the thoracic spinal cord

Area of Science:

• Neuroscience
• Spinal Cord Physiology

Background:

• Renshaw cells are spinal interneurons involved in motor control.
• Previous studies focused on lumbosacral Renshaw cell morphology and axonal branching.
• Thoracic motoneuron inhibition spans larger distances than previously characterized for Renshaw cell projections.

Purpose of the Study:

• To investigate the axonal morphology and termination patterns of Renshaw cells in thoracic spinal cord segments.
• To determine if thoracic Renshaw cell projections differ from lumbosacral projections.
• To assess the relationship between Renshaw cell termination patterns and the extent of motoneuron inhibition.

Main Methods:

• Intracellular neurobiotin labeling of four Renshaw cells in the T7-T8 segments of anesthetized cats.
• Tracing of labeled axons for at least 6 mm from the cell somata.
• Morphological analysis of axonal branching and termination patterns.

Main Results:

• Thoracic Renshaw cell axons exhibited minimal tapering compared to pronounced tapering in lumbosacral axons.
• Axonal termination patterns in the thoracic segments were virtually identical to those observed in the lumbosacral segments.
• No significant morphological differences were found within 6 mm of the soma.

Conclusions:

• The axonal branching and termination patterns of Renshaw cells are conserved across different spinal cord segments.
• The observed termination patterns of Renshaw cells are not directly correlated with the extended range of motoneuron inhibition in thoracic segments.
• Renshaw cell function may involve mechanisms beyond direct axonal projections for modulating widespread inhibition.