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

This research explores the possibility of diagnosing Equine Grass Sickness (EGS), a potentially fatal condition in horses, by identifying chromatolytic subgemmal neurons through biopsies of gustatory papillae. The study could lead to a new benchmark in EGS detection and provides an opportunity to better understand the pathology involving sense of taste.

Objective and Hypothesis

• Equine Grass Sickness (EGS) is a disease that affects horses, causing damage to the nerves of the part of their gut where food is processed. This can be difficult to diagnose.
• The researchers hypothesized that the subgemmal plexus neurons, located in the tongue’s taste buds (gustatory papillae), undergo chromatolysis – a disruptive process where a neuron’s cell body degenerates – during EGS.
• If proven correct, a biopsy of the gustatory papillae can be used to diagnose EGS before the horse dies.
• Moreover, this could provide a spontaneous model to study and better understand the pathology related to the sense of taste.

Methods

• An observational study was conducted where post-mortem samples from 10 EGS-affected and 13 healthy (control) horses were examined.
• Through the use of conventional histology (the study of microscopic structures of tissues) and immunohistochemistry (a process to identify cells in tissues), the researchers compared the subgemmal plexi and gustatory papillae of both groups.

Results

• Chromatolytic neurons were observed in all EGS samples with identifiable neurons. They were found in only one control sample, implying a high correlation between EGS and the presence of chromatolytic neurons.
• Blinded examination of all sections stained with haematoxylin-eosin, a typical staining method in histology, could differentiate between EGS and control horses with high sensitivity and specificity, hence confirming the hypothesis.
• However, the presence of chromatolytic neurons in one control section indicated that multiple sections per horse should be analyzed to ensure diagnostic accuracy.
• No change in taste bud density or morphology, the ratio of taste buds with intragemmal axons, or the percentage of taste buds containing cells undergoing apoptosis, meaning cells in the process of dying, was observed. This indicated the taste buds had enough support from their nerves at the time of sampling.
• All horses with EGS showed no detectable alterations in lingual gland morphology but had an increased proportion of dying serous gland cells in the tongue.

Conclusions

• The identification of chromatolytic subgemmal neurons in post-mortem samples can differentiate EGS and control horses. However, further studies are necessary to evaluate this technique’s effectiveness in diagnosing EGS before death.
• Equine Grass Sickness presents a spontaneous model of subgemmal neuronal chromatolysis, which can contribute to studying and understanding the pathology associated with taste-related structures.