title: Evidence of the Primary Afferent Tracts Undergoing Neurodegeneration in Horses With Equine Degenerative Myeloencephalopathy Based on Calretinin Immunohistochemical Localization.
abstract: Equine degenerative myeloencephalopathy (EDM) is characterized by a symmetric general proprioceptive ataxia in young horses, and is likely underdiagnosed for 2 reasons: first, clinical signs overlap those of cervical vertebral compressive myelopathy; second, histologic lesions--including axonal spheroids in specific tracts of the somatosensory and motor systems--may be subtle. The purpose of this study was (1) to utilize immunohistochemical (IHC) markers to trace axons in the spinocuneocerebellar, dorsal column-medial lemniscal, and dorsospinocerebellar tracts in healthy horses and (2) to determine the IHC staining characteristics of the neurons and degenerated axons along the somatosensory tracts in EDM-affected horses. Examination of brain, spinal cord, and nerves was performed on 2 age-matched control horses, 3 EDM-affected horses, and 2 age-matched disease-control horses via IHC for calbindin, vesicular glutamate transporter 2, parvalbumin, calretinin, glutamic acid decarboxylase, and glial fibrillary acidic protein. Primary afferent axons of the spinocuneocerebellar, dorsal column-medial lemniscal, and dorsospinocerebellar tracts were successfully traced with calretinin. Calretinin-positive cell bodies were identified in a subset of neurons in the dorsal root ganglia, suggesting that calretinin IHC could be used to trace axonal projections from these cell bodies. Calretinin-immunoreactive spheroids were present in EDM-affected horses within the nuclei cuneatus medialis, cuneatus lateralis, and thoracicus. Neurons within those nuclei were calretinin negative. Cell bodies of degenerated axons in EDM-affected horses are likely located in the dorsal root ganglia. These findings support the role of sensory axonal degeneration in the pathogenesis of EDM and provide a method to highlight tracts with axonal spheroids to aid in the diagnosis of this neurodegenerative disease.
authors.affiliation: Department of Veterinary Population Medicine, University of Minnesota, St Paul, MN, USA cjfinno@ucdavis.edu.
authors.forename: C J
authors.initials: CJ
authors.lastname: Finno
authors.affiliation: Department of Veterinary Population Medicine, University of Minnesota, St Paul, MN, USA cjfinno@ucdavis.edu.
authors.forename: S J
authors.initials: SJ
authors.lastname: Valberg
authors.affiliation: Veterinary Diagnostic Laboratory, University of Minnesota, St Paul, MN, USA cjfinno@ucdavis.edu.
authors.forename: J
authors.initials: J
authors.lastname: Shivers
authors.affiliation: Veterinary Diagnostic Laboratory, University of Minnesota, St Paul, MN, USA.
authors.forename: E
authors.initials: E
authors.lastname: D'Almeida
authors.affiliation: Department of Veterinary Population Medicine, University of Minnesota, St Paul, MN, USA Veterinary Diagnostic Laboratory, University of Minnesota, St Paul, MN, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Armién
mesh_terms: D000818:Animals; D001259:Ataxia / Q000473:pathology / Q000662:veterinary*; D001927:Brain Diseases / Q000473:pathology / Q000662:veterinary*; D064026:Calbindins / Q000378:metabolism*; D006734:Horse Diseases / Q000473:pathology*; D006736:Horses; D007150:Immunohistochemistry / Q000662:veterinary; D019636:Neurodegenerative Diseases / Q000473:pathology / Q000662:veterinary; D009474:Neurons / Q000473:pathology; D013116:Spinal Cord / Q000473:pathology; D013118:Spinal Cord Diseases / Q000473:pathology* / Q000662:veterinary*
chemical_list: D064026:Calbindins
keywords: ataxia; calcium-binding proteins; horses; medulla oblongata neuroaxonal dystrophies; spinal cord