A study of residual lesions in horses that recovered from clinical signs of chronic equine dysautonomia

Abstract

Background: Equine dysautonomia (ED) causes degeneration and loss of autonomic neurons. Approximately 50% of chronic cases recover, but it is unclear how they survive neuronal loss.

Objectives: To assess lesions, autonomic neuron numbers, interstitial cells of Cajal (ICC), and neurodegeneration in recovered cases.

Animals: Thirteen cases (group ED), euthanized 10.3 ± 5.2 (1-16) years from diagnosis and 6 age-matched controls (group C).

Methods: Prospective, case control; routine post mortem examination, neuron counts in peripheral and enteric ganglia and immunohistochemical assessment of neural networks (Protein gene product [PGP] 9.5), ICC (c-kit), and neurodegeneration (beta-amyloid precursor protein and ubiquitin) in intestine.

Results: Postmortem findings in group ED were small intestinal dilation (4/12, 33%) and muscular hypertrophy (4/12, 33%), and gastric mucosal hypertrophy (3/11, 27%) and ulceration (4/11, 36%). Neuron density was lower in group ED (mean 39% lower for cranial cervical ganglion [P < .001], median 44% lower in celiacomesenteric ganglion [P = .01]). In intestine, neuronal depletion was worst in ileum (median 100% lower in submucosal plexus [P < .001], 91% lower in myenteric plexus [P = .004]). Group ED had less PGP 9.5 staining in ileal myenteric plexus (mean 66% lower [P = .04]) and circular muscle (median 75% lower [P = .006]). In ileum, there was less c-kit staining in myenteric plexus (median 57% lower [P = .02]) but not muscularis externa. Beta-amyloid precursor protein and ubiquitin results were not indicitive of neurodegeneration.

Conclusions and clinical importance: Intact ICC in muscularis externa might help maintain motility after neuronal loss. Treatment supporting ICC function warrants investigation.

Keywords: BAPP; PGP 9.5; c-kit; dysautonomia; grass sickness; horse; interstitial cells of Cajal; intestinal motility; ubiquitin.