Changes in nasal mucosal innervation in horses with grass sickness

Abstract

Summary Reasons for performing study: Equine grass sickness is a dysautonomia characterised by widespread destruction of autonomic ganglia, resulting in the clinical signs of dysphagia, constipation, profuse sweating, tachycardia, rhinitis sicca and high mortality rate. Rhinitis sicca is a common finding in horses with the chronic form and we have postulated that alterations in autonomic innervation of the nasal mucosa might underlie this clinical presentation. Objectives: In this study, the expression and distribution of nerve fibres immunoreactive for calcitonin gene‐related peptide (CGRP), substance P (SP), the general neuronal marker protein gene‐product 9.5 (PGP 9.5; ubiquitin) and the intermediate neurofilaments (PAN‐N; neurofilaments L, M and H) in the nasal mucosa of normal horses (n = 10) and horses with EGS (n = 18; acute n = 8, subacute n = 3, chronic n = 7) was assessed. Methods: Innervation density and distribution was investigated in the different groups using standard immunohistochemical techniques. Results: Significant differences were noted when comparing the density and distribution of nerve fibres immunoreactive for PGP 9.5 and PAN‐N, with PGP 9.5 consistently giving better staining in all groups and at all sites in the nasal mucosa. An apparent increase in the density of innervation was noted for acute vs. normal cases. A significant reduction in the density of innervation was noted only with PAN‐N when comparing normal horses and acute cases with the chronic group (P<0.05). CGRP and SP immunoreactive nerve fibres were typically most abundant in the epithelial and subepithelial layers, but the quality of staining and nerve fibre density was greater for SP, achieving significant difference in several comparisons. The density of innervation for SP was significantly reduced in the chronic group compared to the normal and acute groups (P<0.01). A significant decrease was noted for CGRP only for the acute and chronic groups (P<0.05). Conclusions: These results demonstrate a reduction in the expression of the sensory neuropeptides in nasal mucosal innervation as a consequence of equine dysautonomia, and may underlie the clinical presentation of rhinitis sicca noted with this disease. Potential relevance: Nasal biopsy may be of use in antemortem diagnosis of grass sickness and identification of mucosal denervation; and might also be useful in the treatment of rhinitis in EGS cases.

Equine grass sickness

“…Prince et al . demonstrated a reduction in the expression of sensory neuropeptides in the nasal mucosal innervation of EGS cases, with a more significant reduction in chronic than in acute cases. This group hypothesised that these alterations may affect the normal mucosal reaction to noxious stimuli, such as vasodilatation and mucus secretion, resulting in drying of the nasal mucosa and contributing to the development of rhinitis sicca.…”

“…Therefore, it remains possible that other factors also contribute to the classic muscle fasciculations associated with EGS. The development of rhinitis sicca is characteristic of chronic EGS and is considered to reflect a loss of innervation in the nasal mucosa, potentially resulting in absent response or inappropriate reaction of the nasal mucosa to noxious stimuli .…”

“…Prince et al . proposed immunohistochemical analysis of nasal biopsies as a potential diagnostic test for EGS, based on the reduction in the expression of the sensory neuropeptides in nasal mucosal innervation. However, in acute cases, only one of the markers assessed showed a significant reduction in expression, while in chronic cases, in which there is less diagnostic urgency, simple visual identification of rhinitis sicca is generally considered diagnostically accurate .…”

Expression of PGP 9.5 by Enteric Neurons in Horses and Donkeys with and without Intestinal Disease

“…All samples were evaluated in blinded fashion on two occasions (1 week apart) by one observer (CF) similar to the technique described by Prince et al (2003). A semiquantitative grading system, as described for previous equine ICC studies (Hudson et al, 2001;Fintl et al, 2004), was used and modified for this study.…”

Equine grass sickness in a donkey

“…However, despite the diagnostic benefits of its presence, severe rhinitis sicca is associated with a poorer prognosis for survival (Milne et al 1994). Although not fully elucidated, the cause of the rhinitis is likely associated with interference to autonomic control of nasal secretions, a hypothesis supported by the reported reduction in sensory neuropeptides expression in the nasal mucosa of EGS cases (Prince et al 2003). The failure of the donkey to develop a typical 'tucked up' ventral abdominal contour is interesting.…”