NORADRENERGIC INNERVATION OF THE RAT SPINAL CORD CAUDAL TO A COMPLETE SPINAL CORD TRANSECTION: EFFECTS OF OLFACTORY ENSHEATHING GLIA

Exp Neurol, 2010 · DOI: 10.1016/j.expneurol.2009.12.008 · Published: March 1, 2010

Spinal Cord Injury Neurology Rehabilitation

Simple Explanation

This study investigates the presence and role of noradrenergic (NA) axons in the spinal cord below the injury site in rats with complete spinal cord transection. The researchers examined whether transplanting olfactory ensheathing glia (OEG), a type of support cell from the olfactory bulb, affects the presence or distribution of these NA axons. The research team found that NA axons were present throughout the spinal cord below the injury, regardless of whether the rats received OEG transplants. These axons appeared to enter the spinal cord from the periphery, via blood vessels and nerve roots, rather than regenerating from the brain. However, OEG transplantation did influence the proximity of NA axons to specific types of nerve cells (cholinergic neurons) associated with motor function. The increased association of NA axons and motor-associated cholinergic neurons may contribute to the improved treadmill stepping observed in OEG-injected spinal rats.

Study Duration

7 Months

Participants

Adult female Wistar Hannover rats

Evidence Level

Not specified

Key Findings

1
NA axons are present throughout the caudal stump of both media- and OEG-injected spinal rats, entering the spinal cord from the periphery via dorsal and ventral roots and along large penetrating blood vessels.
2
OEG transplantation influences the density of DBH-positive axons apposing motor-associated cholinergic neurons; specifically, more NA varicosities were found adjacent to central canal cluster cells, partition cells, and SMNs in the lumbar enlargement of OEG- than media-injected rats.
3
The overall density of NA axons in the caudal stump did not correlate with stepping ability in spinal rats.

Research Summary

This study examined the origin and distribution of noradrenergic (NA) axons in the spinal cord caudal to a complete transection in adult rats, focusing on the impact of olfactory ensheathing glia (OEG) transplantation and treadmill training on these axons. The researchers found that NA axons were present throughout the caudal stump, originating from peripheral sources rather than regenerating from the brain. While the overall density of NA axons did not correlate with stepping ability, OEG transplantation led to increased proximity of NA axons to motor-associated cholinergic neurons. These findings suggest that OEG transplantation may promote reorganization of spinal circuits, influencing the interaction between NA axons and cholinergic neurons, and contributing to improved locomotor ability in spinal rats.

Practical Implications

Rethinking Regeneration Markers

The presence of NA fibers in the caudal spinal cord is not a reliable indicator of coeruleospinal regeneration.

Therapeutic Targeting

The interaction between NA varicosities and motor-associated cholinergic neurons can be targeted for therapeutic intervention to promote locomotor recovery.

OEG Mechanisms

OEG transplantation promotes reorganization of NA axons that interact with the existing spinal locomotor networks in the caudal stump.

Study Limitations

1
The study did not distinguish between synaptic and non-synaptic release of noradrenaline.
2
The origin of NA axons was determined through immunohistochemistry and anatomical observation, lacking direct tracing experiments to confirm the origin of these axons unequivocally.
3
The study acknowledges the potential influence of rat strain on spinal NA innervation, highlighting a need for caution when generalizing these findings across different strains.

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