Abstract
Equine recurrent laryngeal neuropathy (RLN) is a naturally occurring model of length-dependent axonopathy characterized by asymmetrical degeneration of recurrent laryngeal nerve axons (RLn). Distal RLn degeneration is marked, but it is unclear whether degeneration extends to include cell bodies (consistent with a neuronopathy). With examiners blinded to RLN severity, brainstem location, and side, we examined correlations between RLN severity (assessed using left distal RLn myelinated axon count) and histopathological features (including chromatolysis and glial responses) in the nucleus ambiguus cell bodies, and myelinated axon count of the right distal RLn of 16 horses. RLN severity was not associated with RLn cell body number (P > .05), or degeneration. A positive correlation between the left and right distal RLn myelinated axon counts was identified (R2 = 0.57, P < .05). We confirm that RLN, a length-dependent distal axonopathy, occurs in the absence of detectable neuronopathy.
Highlights
Equine recurrent laryngeal neuropathy (RLN) is a naturally occurring model of length-dependent axonopathy characterised by asymmetrical degeneration of recurrent laryngeal nerve axons (RLn)
We investigated two hypotheses: (1) Horses with a more severe RLN phenotype (i.e low myelinated axon count in the left recurrent laryngeal nerve) show degeneration and have fewer cell bodies in their nuclei ambigui compared to horses with a less severe RLN phenotype and (2) these changes will be more pronounced in the left nucleus ambiguus compared to the right
Cell Body Numbers The nucleus ambiguus could be identified in all horses (n=16), where tissue was present for that region
Summary
Equine recurrent laryngeal neuropathy (RLN) is a naturally occurring model of length-dependent axonopathy characterised by asymmetrical degeneration of recurrent laryngeal nerve axons (RLn). Distal RLn degeneration is marked, it is unclear whether degeneration extends to include cell bodies (consistent with a neuronopathy). Methods: With examiners blinded to RLN severity, brainstem location and side, we examined correlations between RLN severity (assessed using left distal RLn myelinated axon count) and histopathological features (including chromatolysis and glial responses) in the nucleus ambiguus cell bodies, and myelinated axon count of the right distal RLn of 16 horses. A positive correlation between the left and right distal RLn myelinated axon counts was identified (R2=0.57, p
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