Neuronal chromatolysis in the subgemmal plexus of gustatory papillae in horses with grass sickness

REASONS FOR PERFORMING STUDY: Diagnosis of equine grass sickness (EGS) can be challenging. We hypothesised that subgemmal plexus neurons are chromatolytic in EGS. If correct, histopathologic examination of gustatory papillae biopsies could aid pre-mortem 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.

STUDY DESIGN: 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% CI 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. EGS was not associated with alterations in taste bud density or morphology, proportion of taste buds with neurofilament immunopositive intragemmal axons and proportion of taste buds containing cells undergoing apoptosis, suggesting taste buds had adequate neurotrophic support at the time of sampling. EGS horses 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 pre-mortem EGS diagnosis. EGS represents a spontaneous model of subgemmal neuronal chromatolysis that facilitates study of the pathology of structures involved in taste. This article is protected by copyright. All rights reserved.