Evidence of the Primary Afferent Tracts Undergoing Neurodegeneration in Horses With Equine Degenerative Myeloencephalopathy Based on Calretinin Immunohistochemical Localization.

This research paper seeks to understand more about Equine Degenerative Myeloencephalopathy (EDM), a neurodegenerative disease in horses, focusing on the part of the nervous system known as the primary afferent tracts. The research provides evidence of neurodegeneration in these areas, particularly in dampening sensitivity pathways, as a contributing factor to EDM, revealed through the use of specific protein markers (calretinin).

Objectives of the Study

• The primary aim of the study was to use immunohistochemical (IHC) markers to trace axons (nerve fibres) in healthy horse’s neurologic pathways, namely spinocuneocerebellar, dorsal column-medial lemniscal, and dorsospinocerebellar tracts.
• The secondary objective was to identify the IHC staining characteristics of neurons and degenerated axons along the pathways associated with sensations in horses affected by EDM.

Experimental Procedure

• This study involved exploring the brains, spinal cords, and nerves of two healthy control horses, three EDM-affected horses, and two other disease control horses.
• IHC staining for various proteins, including calbindin, vesicular glutamate transporter 2, parvalbumin, calretinin, glutamic acid decarboxylase, and glial fibrillary acidic protein was done.
• The primary afferent axons of three tracts were successfully traced using calretinin, a calcium-binding protein widely used as a marker for neurons and nerve fibres.

Study Results

• In the dorsal root ganglia, a group of neurons in the spinal cord, researchers found calretinin-positive cell bodies. The findings suggest that calretinin IHC may be used to trace axonal projections from these cells.
• Among the EDM-affected horses, calretinin-immunoreactive spheroids (markers of axonal damage) were observed within the nuclei cuneatus medialis, cuneatus lateralis, and thoracicus. However, neurons within these nuclei were lacking in calretinin.
• It is likely that the cell bodies of degenerated axons in horses with EDM are located in the dorsal root ganglia.

Conclusion

• The findings reaffirm the role of sensory axonal degeneration in the onset of EDM and suggest a new method to trace tracts with axonal spheroids, all of which could assist in diagnosing this disease.
• The use of calretinin as an effective tool to visualize neurons and nerve fibres could be significant in the study and understanding of the disease as it highlights the specific pathways affected, making the disease easier to diagnose.