title: Neuronal chromatolysis in the subgemmal plexus of gustatory papillae in horses with grass sickness.
abstract: BACKGROUND
  Diagnosis of equine grass sickness (EGS) can be challenging. We hypothesised that subgemmal plexus neurons are chromatolytic in EGS. If correct, histopathological examination of gustatory papillae biopsies could aid premortem diagnosis of EGS, and EGS could represent a spontaneous model of subgemmal neuronal chromatolysis to facilitate study of the pathology of structures involved in taste.
  
  
  OBJECTIVE
  To compare subgemmal plexi and gustatory papillae in EGS and control horses.
  
  
  METHODS
  Observational study.
  
  
  METHODS
  Conventional histology and immunohistochemistry were used to compare subgemmal plexi and gustatory papillae in post mortem samples from 10 EGS and 13 control horses.
  
  
  RESULTS
  Chromatolytic neurons were present in all 57 EGS sections which had identifiable neurons, and in only one of 57 control sections. Blinded examination of all haematoxylin-eosin stained sections from each horse for chromatolysis facilitated accurate differentiation of EGS and control horses, with a sensitivity of 100% (95% confidence interval 93.7-100) and specificity of 98.2% (90.6-100) for diagnosing EGS; however, the presence of chromatolytic neurons in one control section indicated that multiple sections per horse must be analysed to achieve diagnostic accuracy. Equine grass sickness was not associated with alterations in taste bud density or morphology, proportion of taste buds with neurofilament immunopositive intragemmal axons or proportion of taste buds containing cells undergoing apoptosis, suggesting taste buds had adequate neurotrophic support at the time of sampling. Horses with EGS had no detectable alteration in lingual gland morphology, but had increased proportions of apoptotic lingual serous gland cells.
  
  
  CONCLUSIONS
  While identification of chromatolytic subgemmal neurons in post mortem samples correctly differentiated EGS and control horses, further study is required to evaluate this technique for premortem EGS diagnosis. Equine grass sickness represents a spontaneous model of subgemmal neuronal chromatolysis that facilitates study of the pathology of structures involved in taste.
authors.affiliation: Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, UK. bruce.mcgorum@ed.ac.uk.
authors.forename: B C
authors.initials: BC
authors.lastname: McGorum
authors.affiliation: Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, UK.
authors.forename: R S
authors.identifier: http://orcid.org/0000-0003-0546-0578
authors.initials: RS
authors.lastname: Pirie
authors.affiliation: Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, UK.
authors.forename: D
authors.initials: D
authors.lastname: Shaw
authors.affiliation: Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, UK.
authors.forename: N
authors.initials: N
authors.lastname: Macintyre
authors.affiliation: Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, UK.
authors.forename: A
authors.initials: A
authors.lastname: Cox
mesh_terms: D000818:Animals; D017209:Apoptosis; D001342:Autonomic Nervous System Diseases / Q000473:pathology / Q000662:veterinary*; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis / Q000473:pathology*; D006736:Horses; D008297:Male; D009412:Nerve Fibers / Q000378:metabolism; D009474:Neurons / Q000473:pathology*; D013650:Taste Buds / Q000473:pathology*; D014059:Tongue / Q000294:innervation*
keywords: chromatolysis; grass sickness; gustatory papillae; horse; subgemmal plexus