Cholinergic activity of intestinal musclein vitro taken from horses with and without equine grass sickness

Equine grass sickness (EGS) is a pan-dysautonomia of horses that involves central and peripheral neuronal degeneration and ultimately depletion. This is the first reported functional study on the motility of equine intestine taken immediatelypost mortem from horses with EGS. Strips of smooth muscle from the small intestine of healthy and EGS-affected horses were suspended in an organ bath and their motility was measured isometrically. The activity of the cholinergic system was studied. Physostigmine enhanced the motility of all muscle strips. Tissues taken from horses suffering from acute grass sickness (AGS) had the longest latency before a measurable response could be obtained (p<0.05). The ileum appeared to be damaged by EGS to a greater extent than the duodenum. For the duodenal strips the enhanced rate of spontaneous contractions was significant (p<0.05) for both normal tissue and that affected by grass sickness but this was not the case for the ileal strips. Muscarinic receptor sensitivity investigation using bethanecol suggested a hypersensitivity of receptors with AGS material,Abbreviations AGS acute grass sickness - CGS chronic grass sickness - ED₅₀ median effective dose - EGS equine grass sickness - VIP vasoactive intestinal peptide     

Systemic concentrations of antioxidants and biomarkers of macromolecular oxidative damage in horses with grass sickness

REASONS FOR PERFORMING STUDY: The aetiopathogenesis of equine grass sickness (EGS) is unknown. The role of free radical-mediated neuronal damage has not previously been investigated in this condition. OBJECTIVES: To investigate the potential contribution of oxidative damage and antioxidant status to neurodegeneration in EGS. METHODS: Systemic levels of surrogate biomarkers were determined in 10 horses with acute EGS and in 2 control populations; 10 healthy horses co-grazing with the 10 EGS horses at the onset of clinical disease, and 10 healthy mares grazing where EGS has not been reported. RESULTS: EGS horses had alterations in levels of several antioxidants, consistent with oxidative stress, the acute phase response and/or the secondary metabolic complications of EGS. EGS horses had elevated plasma dihydroxyphenylalanine (DOPA) levels. CONCLUSIONS: The elevated DOPA levels probably reflected a generalised disturbance of catecholamine metabolism rather than increased DOPA production via free radical-mediated oxidation of tyrosine. However, there was no evidence of systemic macromolecular oxidative damage. POTENTIAL CLINICAL RELEVANCE: Further work is required to determine whether macromolecular oxidative damage occurring at the neuronal level contributes to EGS.     

Pathological changes caused by Anoplocephala perfoliata in the mucosa/submucosa and in the enteric nervous system of equine ileocecal junction

In this study, pathological changes caused by Anoplocephala perfoliata in the ileocecal junction were investigated in 31 regularly slaughtered mixed-breed horses of both sexes. Our results showed a significant relationship between parasite burden and grading of histopathological lesions in the mucosa and submucosa. Hypertrophy of the circular muscle layer was found in infected horses. Moreover, enteric nervous system evaluation showed a significant injury of intestinal nervous elements in the horses with moderate to high parasitism expressed as an increase of degenerative-regressive changes in neuronal cells and a decrease in the number of myenteric ganglia and neuronal cells. These findings can help to clarify the pathogenesis of intestinal motility disorders associated with A. perfoliata infection in horses.     

Tissue Culture of the Enteric Nervous System from Equine Ileum

Ileal samples were harvested fresh from euthanized adult horses. The tissues were microdissected to prepare wholemount preparations for immunohistochemistry and for either explant or dissociated culture systems of the enteric nervous system. Explant culture systems were established using wholemounts of either the submucous plexus or the muscularis externa (including the myenteric plexus). Dissociated cell cultures could only be obtained from the submucous plexus. Culture systems were maintained for up to 5 days. Immunoreactivity for a neuronal marker (Pan-N) and for glial cell markers (GFAP and S100) indicated the presence of both neurons and enteric glia in the tissue culture preparations.This is the first report of equine enteric neurons being grown in tissue culture. Further refinements to the techniques will be required before this in vitro model can be used for quantitative analysis.     

The association of Clostridium botulinum type C with equine grass sickness: a toxicoinfection?

The cause of grass sickness, an equine dysautonomia, is unknown. The disease usually results in death. Gastrointestinal (GI) dysfunction is a common clinical manifestation in all forms of the disease. It is generally thought that equine grass sickness (EGS) is caused by an ingested or enterically produced neurotoxin which is absorbed through the GI tract. Clostridium botulinum was first implicated as a causative agent when it was isolated from the GI tract of a horse with EGS in 1919. The aim of the present study was to investigate the hypothesis that EGS results from toxicoinfection with C. botulinum type C: growth of the bacterium in the GI tract with production of toxin (BoNT/C). Ileum contents and faeces from horses with EGS were investigated for BoNT/C, and indirectly for the presence of C. botulinum type C, and compared with control samples from horses without EGS. BoNT/C was detected directly by ELISA in the ileum of 45% (13/29) of horses with EGS compared to 4% (1/28) of controls, and in the faeces of 44% (20/45) of horses with EGS compared to 4% (3/77) of controls. Levels of up to 10 Mlg toxin/g wet weight of gut contents were observed. The one control horse with detectable toxin in the ileum had been clinically diagnosed as having acute EGS, but this was not confirmed by histopathology. The organism was detected indirectly by assaying for BoNT/C by ELISA after enrichment in culture medium. C. botulinum type C was shown to be present in 48% (14/29) of ileum samples and 44% (20/45) of faecal samples from horses with EGS, compared with 7% (2/27) of ileum samples and 8% (6/72) of faecal samples from controls. These results support the hypothesis that EGS results from a C. botulinum type C toxicoinfection.     

Development of a clinical prediction score for detection of suspected cases of equine grass sickness (dysautonomia) in France

Equine grass sickness (EGS) (equine dysautonomia) is a neurodegenerative condition of grazing equines. Pre-mortem diagnosis of EGS is a challenge for practitioners as definitive diagnosis requires ileal/myenteric lymph node biopsies. This study aimed to develop a clinical score that could be used by practitioners to improve the detection of acute or subacute EGS cases in the field. Suspected EGS cases were declared by veterinary practitioners. A case was classified as confirmed positive if ileal or rectal biopsy samples showed neuronal degeneration typical of EGS. A semi-quantitative scoring system, including epidemiological and clinical data, was created to attempt to classify suspected EGS horses into confirmed positive or negative cases. Each variable was weighted based on a boosted regression trees model, while taking into account its clinical relevance. Twenty-eight EGS cases were confirmed by biopsy during the entire study period. The best cut-off value for the score to have a high sensitivity while maximizing specificity was 8, with a sensitivity of 100% and a specificity of 53%. In our dataset, 77% of animals would be correctly classified with this cut-off value of 8. Highest sensitivity was chosen in order to detect the highest number of potential cases. Our score represents an inexpensive and useful tool to aid in the identification of suspected EGS cases in the field and selection for further diagnostics procedures to confirm or rule out the disease. Application of the score to larger populations of animals would be required to further adapt and refine the score.     

Outbreaks of equine grass sickness in Hungary

Equine grass sickness (EGS) occurs mainly in Great Britain, but has once been reported in Hungary. The stud which was affected by EGS in 2001 had no new cases until 2009/10, when 11 of 60 and five of 12 one- to three-year-old colts died or were euthanased due to EGS. Following a few hours in the high-risk field during the winter of 2010/11 further four cases of acute EGS were noted among these horses. The affected horses showed somewhat different clinical signs compared with the cases reported in Great Britain. Histopathological findings in these horses were consistent with EGS. In most examined cases carbofuran, a carbamate was found in the liver by toxicological examination, and it is postulated that carbofuran may influence the immune system and therefore predispose the horses to develop EGS. Carbamates are thought to cause a delayed neurotoxicity in human beings. Further studies are needed to clarify the potential role of carbamates in EGS.     

Nonruminant Nutrition Symposium: Involvement of gut neural and endocrine systems in pathological disorders of the digestive tract

The functioning of the gastrointestinal tract is under the control of the most extensive system of peripheral neurons in the body, the enteric nervous system, and the largest endocrine system of the body, the GEP endocrine system. The enteric nervous system in large mammals contains 500 million neurons, and the GEP endocrine system produces more than 30 hormones. Numerous enteric neuropathies affecting both humans and animals have been described and digestive disorders affect commercially important species, such as horses and cattle. The most severe enteric neuropathies (e.g., lethal white syndrome in horses or Hirschsprung's disease in humans) can be fatal. Also, horses with ileus or other digestive disorders are commonly euthanized. In this review we discuss examples of enteric neuropathies that affect agricultural animals and humans: prion disease, postoperative ileus, distal enteric aganglionosis, and infective diarrhea. Enteric neurons and glia are a location of prion proteins and are involved in transmission of the infection from gut to brain and brain to gut. Postoperative ileus is a complex disorder involving the local inhibitory effects of sympathetic nervous system activation and the release of opioids, presumably from enteric neurons. Intestinal inflammation, especially of the external muscle that includes enteric ganglia, also occurs in ileus. Congenital distal bowel aganglionosis, responsible for lethal white syndrome in horses, Hirschsprung's disease in humans, and similar conditions in mice and rats, is a fatal condition if untreated. Mutations of the same genes can cause the condition in each of these species. The only effective current treatment is surgical removal of the aganglionic bowel. Infectious diarrheas involve activation of enteric secretomotor neurons by pathogens and the toxins they produce, which causes substantial fluid loss. Strategies to target enteric neurons in the treatment of secretory diarrheas have not been developed. Disorders of enteroendocrine cells, other than GEP endocrine tumors, are less well documented. However, evidence for the involvement of gut endocrine cells in a subset of patients with irritable bowel syndrome, and in the symptomology of celiac disease, has been demonstrated. Further investigation of the involvement of enteric neural and endocrine signaling systems in digestive disorders, especially in agricultural and companion animals, may lead to diagnostic and therapeutic advances.     

Prevalence of Clostridium perfringens in faeces and ileal contents from grass sickness affected horses: Comparisons with 3 control populations

Reasons for performing study: While previous studies have demonstrated an association between equine grass sickness (EGS) and the presence of Clostridium botulinum within ileal contents and faeces, no such associations with other intestinal‐derived anaerobic bacteria have been extensively investigated. Hypothesis: The prevalence of C. perfringens in the ileal contents and faeces of EGS horses is greater than control horses; the detection of C. perfringens in faeces by ELISA could be diagnostically beneficial in a clinical setting. Methods: The prevalence of C. perfringens in faeces from EGS horses and healthy grazing control horses was determined by both selective culture and ELISA to permit both validation of the ELISA and inter‐group comparisons. Additionally, the prevalence of C. perfringens (ELISA) in ileal contents from EGS horses was compared with that for control horses with nongastrointestinal disease. Finally, the prevalence of C. perfringens (ELISA) in faeces from EGS cases was compared with that from both horses with which they shared pasture at the time of disease onset and non‐EGS colic horses. Results: When compared with culture, the ELISA had a sensitivity and specificity of 86 and 98%, respectively. The prevalence of C. perfringens in faeces as determined by both culture and ELISA was significantly higher (P<0.001) for EGS horses (7/9 and 15/37, respectively) than for healthy grazing controls (0/60 and 1/74, respectively). The prevalence of C. perfringens in ileal contents from EGS horses (5/10) was greater than that for horses with nongastrointestinal disease (1/12) at a level that approached significance (P = 0.056). EGS cases had a significantly greater prevalence of C. perfringens in faeces (15/37) than co‐grazing horses (1/18) and colic (1/16) horses. The specificity (93%) and PPV (94%) of the detection of C. perfringens by ELISA on faecal samples in relation to disease status (EGS compared with colic horses) was good. Sensitivity (41%) and NPV (39%) were poor. Conclusions and potential relevance: The use of a commercial ELISA to detect faecal C. perfringens may be diagnostically beneficial when differentiating EGS cases from colic cases, although further work is required to fully evaluate its potential.     

An acute outbreak of equine dysautonomia (equine grass sickness) in a group of eight Przewalski's horses (Equus ferus [caballus] przewalskii)

Equine grass sickness (EGS) is a neurodegenerative disease affecting grazing equids of which a single case of the chronic clinical presentation has previously been reported in a Przewalski's horse (Equus ferus [caballus] przewalskii). A group of 8 Przewalski's horses were moved to a new enclosure, recently vacated by a group of 4 Eastern kiang (Equus kiang holdereri) that showed no evidence of disease. After 23 days the first Przewalski's horse showed clinical signs of acute EGS including flank sweating, belly kicking, rapid loss of body condition, cessation of faecal passage, nasogastric reflux and mouthing water. It was subjected to euthanasia within 48 h due to lack of therapeutic response. Within 24 h of this first case developing clinical signs, a further 5 Przewalski's horses showed similar clinical signs of acute EGS and were subjected to euthanasia. Post mortem examinations confirmed acute EGS, with all animals demonstrating typical chromatolysis, cytoplasmic hypereosinophilia, cellular swelling, vacuolation, pyknosis and loss of nuclei in approximately 90% of neurones in the cranial cervical and cranial mesenteric ganglia and myenteric and submucosal plexi of the ileum. Two Przewalski's horses within the group showed no clinical signs of disease. No single pathogen was identified as the causal agent, but the epidemiological pattern of the outbreak was typical for that previously reported for acute EGS in domestic equids. All affected animals and the 2 surviving Przewalski's horses had low antibody titres to Clostridium botulinum type C. This is the first report of acute EGS in a herd of Przewalski's horses.     

Systemic antibodies to Clostridium botulinum type C: do they protect horses from grass sickness (dysautonomia)?

The aetiology of equine grass sickness (EGS) is still unknown. There is increasing evidence that toxicoinfection with Clostridium botulinum type C is involved. Epidemiological evidence shows that resistance to EGS can occur in older horses and those that have been on a particular pasture for longer or have been in prior contact with the disease. This resistance may be in the form of an immune response to the aetiological agent. Levels of systemic antibodies to the surface antigens of C. botulinum type C (using the closely related and safe C. novyi type A as a phenotypic marker) and to the botulinum type C neurotoxin (BoNT/C) were investigated in horses with and without EGS. Horses with grass sickness were found to have significantly lower levels of systemic IgG to both surface antigens and BoNT/C. Horses with low levels of systemic immunity to these antigens may be more susceptible to developing EGS. There were no significant differences in antibody levels between the different categories of EGS, suggesting systemic immunity to C. botulinum type C does not play a significant role in influencing the severity of the disease. However, horses that had been in contact with EGS or that were grazing land where it had occurred frequently in the past had significantly higher antibody levels to these antigens. These horses may have been exposed to subclinical doses of C. botulinum type C and BoNT/C, resulting in the production of a protective immune response against the putative aetiological agent. This finding is of potential significance for the prospect of prevention of EGS by vaccination against C. botulinum type C.     

An epidemiological study of risk factors associated with the recurrence of equine grass sickness (dysautonomia) on previously affected premises

REASONS FOR PERFORMING STUDY: The reasons why equine grass sickness (EGS) recurs on premises are unknown and, consequently, practical methods for reducing the risk of recurrence are not available. OBJECTIVES: To identify risk factors associated with recurrence of EGS on premises and to gain possible insights into the pathogenesis of the disease. METHODS: Data on disease history and risk factors were collected by postal questionnaire from premises with EGS cases between 1st January 1997 and 31st December 2001. Data on variation in rates of recurrence of EGS for different risk factors were analysed using Poisson regression analysis. RESULTS: Of 509 premises contacted, 305 (60%) returned useable questionnaires and 100 of these (33%) were classified as 'recurrent' premises. An overall median incidence rate for EGS of 2.1 EGS incidents/100 horses/premises/year was recorded. There was an increased rate of recurrence with higher numbers of horses, presence of younger animals, stud farms and livery/riding establishments, loam and sand soils, rearing of domestic birds and mechanical droppings removal. The rate of recurrence decreased with chalk soil, cograzing ruminants, grass cutting on pastures and removal of droppings by hand. Several statistically significant interactions were identified. CONCLUSIONS: Many of the findings are consistent with the theory that EGS is a toxico-infectious form of botulism. Several of the significant factors identified may directly or indirectly relate to soil disturbance and consequent soil contamination of grass, thereby increasing the rate of exposure of grazing horses to Clostridium botulinum, which resides in soil. Potential relevance: Identification of potentially modifiable risk factors may, ideally following validation in appropriately designed, controlled and randomised intervention studies, lead to practical measures to reduce the incidence of EGS on previously affected premises.     

A comparative study of the intestinal microbiota of healthy horses and those suffering from equine grass sickness

This study compares quantitatively the microbiota of the gastrointestinal tract of healthy horses with that of horses with equine grass sickness (EGS). Faecal and ileal samples were cultured quantitatively on selective and non-selective media. Confirmed anaerobes were identified to species level.Overall faecal counts gave a ratio of aerobes:anaerobes of approximately 1:1. However, the mean counts in healthy horses of 4.4x10(8) aerobes:3.7x10(8) anaerobes per gram wet weight were different from counts in EGS (means were 10-100-fold higher), with statistically significant differences for the anaerobes (p=0.04). There were 10-100-fold more anaerobic cocci in EGS samples compared to healthy controls. Most of the seven species of anaerobic cocci were found in both healthy horses and EGS. Differences in clostridia isolated between health and disease were notable: fourteen species were isolated from EGS cases, compared to only one (C. bifermentans) in controls. The mean faecal clostridial counts in chronic disease were higher than in controls (10-fold) and in acute EGS (100-fold). In contrast, mean counts for ileal samples from acute cases, showed a 10-fold increase for clostridia compared to 1000-fold reduction in chronic cases (compared to faecal counts). Results indicate an increase in the bacterial numbers in the GI tract of animals with EGS compared to the controls and clostridia are prominent in EGS. Whether the increase in clostridia is the cause of GI stasis or a consequence remains uncertain.     

Equine grass sickness is associated with low antibody levels to Clostridium botulinum: a matched case-control study

REASONS FOR PERFORMING STUDY: Equine grass sickness is a high mortality disease which, despite many years of investigation, is of unknown aetiology. Recent findings indicating that the disease is associated with Clostridium botulinum require support from an epidemiological study that recognises and controls for potential confounders, e.g. age, time of year and premises. HYPOTHESIS: EGS is associated with low antibody levels to C. botulinum antigens. METHODS: A matched case-control study was conducted. Data were collected from 66 histologically confirmed cases of EGS and 132 premises-matched control horses. The probability of EGS in horses was modelled using conditional logistic regression. RESULTS: EGS was significantly associated (age-adjusted P < 0.005) with low antibody levels to each of 3 clostridial antigens; C. botulinum type C and C. novyi type A surface antigens and a C. botulinum type C toxin complex toxoid. These serological risk factors for EGS remained highly significant when entered into multivariable models. This study also identified new horse-level risk factors for EGS; feeding hay or haylage was associated with a decreased risk of disease, change of feed type or quantity during the 14 days prior to disease was associated with increased risk, and the use of an ivermectin anthelmintic at both the ultimate and penultimate treatments was also associated with a significantly increased risk of EGS. CONCLUSIONS: This study provides strong support for the role of C. botulinum in the aetiology of EGS and identifies managemental risk factors for the disease. POTENTIAL RELEVANCE: Increasing anticlostridial antibody levels by vaccination and appropriate managemental interventions may decrease the risk of EGS occurring.     

The role of quantitative electromyography (EMG) in horses suspected of acute and chronic grass sickness

REASONS FOR PERFORMING THE STUDY: Clinical evidence of motor neuron involvement in equine grass sickness (EGS) has not been reported. HYPOTHESIS: Quantitative electromyography (EMG) analysis can elucidate subtle changes of the lower motor neuron system present in horses with EGS, performed ante mortem. METHODS: Fourteen horses diagnosed clinically with acute, subacute or chronic EGS were examined and quantitative EMG performed. Previously published data on healthy horses and horses with proven lower motor neuron disease (LMND) were used as controls. In 8 horses post mortem examination was performed, and in 7 muscle biopsies of the lateral vastus muscle underwent histopathology and morphometry. RESULTS: Clinical electrophysiological evidence of neuropathy was present in 12 horses. Analysis of data from the first 4 horses resulted in 95% confidence intervals (CI) of nontransformed data for motor unit action potential (MUP) duration in subclavian, triceps and lateral vastus muscle of 11.0-13.7, 14.8-20.3 and 12.2-17.2 msecs, respectively, and for MUP amplitude 291-453, 1026-1892 and 957-1736 microV, respectively. For number of phases the 95% CI was 3.6-4.4, 2.9-3.6 and 2.9-3.4, respectively, and for number of turns 5.0-6.5, 4.3-5.3 and 3.7-4.6, respectively. No changes in duration of insertional activity were measured. Pathological spontaneous activity was observed in all horses. EGS as evidenced by degenerative changes in the autonomic ganglia in combination with minor degenerative changes of the spinal lower motor neurons was observed on post mortem examination in all 8 available autopsies. In muscle biopsies of 4 out of 7 horses changes consistent with slight neurogenic atrophy were found. CONCLUSIONS AND POTENTIAL RELEVANCE: EMG results demonstrated the presence of a neuropathy of skeletal muscles in all horses suspected to have EGS. The combination of clinical and electrophysiological evidence may aid differential diagnosis of neurogenic disease in cases of weight loss and colic.     

Seroprevalence of antibotulinum neurotoxin type C antibodies in horses in Israel

REASONS FOR PERFORMING STUDY: Clostridium botulinum type C is prevalent in Israel and outbreaks recorded in many species, other than horses. Association between levels of anti-BoNT/C antibodies and equine grass sickness (EGS) have been demonstrated but seroprevalence of anti-BoNT/C antibodies in horses has not been reported nor has EGS been reported in Israel. OBJECTIVES: To determine the seroprevalence of specific anti-BoNT/C antibodies in horses in Israel and to determine whether age, breed and gender, or geographical region of farms are potential risk factors for exposure to BoNT/C. HYPOTHESIS: Anti-BoNT/C antibodies are prevalent among horses in Israel and farm and horse-level variables are associated with increased risk for exposure. METHODS: Serum samples from 198 horses were collected and the levels of specific anti-BoNT/C antibodies were determined using enzyme-linked immunosorbent assay (ELISA). For each categorical variable indicator variables were created and the odds ratio (OR) and 95% confidence intervals (95% CI) for the outcome variable were calculated using a univariable and multivariable logistic regression models. RESULTS: A total of 61 (30.8%) horses were ELISA positive for anti-BoNT/C IgG antibodies. The farm and its geographical region were associated significantly with seropositivity, horse-level variables, such as gender and breed, were also associated with seropositivity. Quarter Horse and Warmblood mares placed in the southern region of Israel had the highest odds to be tested positive for anti-BoNT/C IgG antibodies. CONCLUSIONS AND POTENTIAL RELEVANCE: Several farm and various horse-level risk factors for exposure to BoNT/C, found in this study, could be correlated to previously reported risk factors of EGS. Studies are required to determine the predisposing factors that cause EGS, which is apparently not present in Israel.     

Polyneuropathy associated with forage sources in Norwegian horses

BACKGROUND: Cases of hindlimb digital extensor weakness of unknown etiology have been observed in Norway since 1995. HYPOTHESIS: We hypothesized that the observed bilateral extensor weakness was attributable to neuropathy of the distal nerves and that this was related to environmental factors, possibly dietary. ANIMALS: Seventy-five horses with digital extensor weakness occurring from 1995 to 2004 are described. METHODS: Eleven horses were examined at The Norwegian School of Veterinary Science, and the medical records of 64 horses seen in ambulatory practice were reviewed. RESULTS: There was no apparent sex, age, or breed predilection, but the majority were horses kept for pleasure or breeding purposes. Clinical signs varied from intermittent knuckling of the hindlimbs to paraplegia. Some horses showed no or only slow progression of signs, whereas others developed severe signs within hours. No other neurologic deficits were detected in any of the horses. Epidemiologic data and laboratory results were not supportive of an infectious etiology. The only common factor for all affected horses seemed to be feeding big bale silage or, occasionally, hay of poor microbiologic quality. Forty of the 75 horses were euthanized. Histopathologic examination of peripheral nervous tissue was performed in 22 horses, all of which had neuronal fiber degeneration. The majority of horses with mild signs recovered after 5-6 months of rest. CONCLUSIONS AND CLINICAL IMPORTANCE: Clinical signs correlated with polyneuropathy involving sciatic nerves.     

Light Microscopy of the Enteric Nervous System of Horses with or without Equine Dysautonomia (Grass Sickness): its Correlation with the Motor Effects of Physostigmine

Light microscopy was undertaken on sections from the caudal flexure of the duodenum and the terminal ileum proximal to the ileocaecal fold in 5 control horses, 5 horses with acute grass sickness (AGS), and 5 horses with chronic grass sickness (CGS). With the exception of the ileal submucous plexus of the CGS group, the AGS group had the lowest number of neurons as measured using a subjective scoring scheme. The proportion of abnormal neurons in the AGS group was similar in both plexuses and both regions, whereas the values for the CGS group were much higher in the duodenal region than in the ileal region. The motility of tissue adjacent to that used for histology was measured isometrically in vitro. The increase in the rate of contractions following exposure to physostigmine was greatest for the AGS group, both from the duodenal and from the ileal region. The latency was longest for the AGS group, suggesting that the material from this group had the least number of active cholinergic neurons. The studies with physostigmine thus indicated that the most severe functional damage occurred in cases of AGS. These findings confirm that extensive damage occurs in the enteric neurons in equine grass sickness. There was good correlation between the functional cholinergic responses and the extent of neuronal degeneration.     

Histological and immunohistochemical studies of changes in myenteric plexuses and in interstitial cells of Cajal associated with equine colic

In this study we investigated the histological changes of the myenteric plexuses and interstitial cells of Cajal (ICC) in gut samples from horses with colic to try to find results useful in the prognostic evaluation of enteric lesions. A morphologic and quantitative study of myenteric ganglia, ganglion cells and neuronal chromatolytic and necrotic changes of 24 horses with colic was performed. For ganglion cells, enteroglial cells and ICC immunolabeling was also performed to identify cell functional disorders. A significant increase of neuronal chromatolysis and necrosis occurred in horses suffering from colic throughout the gut. The neuron-specific enolase (NSE) and synaptophysin immunoreaction quantified with image analysis showed a significant loss of neuronal activity in all intestinal tracts of the animals under study associated with a significant loss of ICC immunoreactivity. The results supports immunohistochemical evaluation of ENS and ICC as a useful tool along with morphometric investigations in the evaluation of gut lesions produced during colic syndrome.     

Pathological changes caused by Anoplocephala perfoliata in the equine ileocecal junction

Gastrointestinal motility disorders represent a significant cause of morbidity and mortality in horses. Previously regarded as a non-pathogenic tapeworm, Anoplocephala perfoliata has been recently associated with equine colic. In this study, pathological changes related to A. perfoliata at the ileocecal junction were investigated in 31 slaughtered horses. Our results showed a significant relationship between parasitic burden and grading of histopathological lesions in both the mucosa and submucosa. Moreover, in infested horses, hypertrophy of the circular muscle layer was determined. Finally, an enteric nervous system (ENS) evaluation showed injury to intestinal nervous elements in horses with moderate to high parasitism. In summary, our results on the ENS support a correlation between colic and A. perfoliata infestion in the horse.