Biomedical subjects
Publications and source records attributed to I G Mayhew.
Electromyography was used as an aid to the diagnosis of equine motor neuron disease in a conscious horse while it was under caudal epidural anaesthesia. A muscle biopsy was taken to confirm the diagnosis which was then supported by a postmortem examination.
Equine grass sickness (EGS) is an acquired disease of unknown aetiology affecting horses kept at grass. The disease is characterised by postganglionic sympathetic and parasympathetic neuronal pathology and is categorised as a dysautonomia. This study undertook a systematic examination of brain stem cranial nerve nuclei in 59 cases of EGS. Pathology consisting of neuronal chromatolysis was most consistently noted in the lower motor neurons of the general visceral efferent nucleus of CN III and X and the general somatic efferent nuclei of CN III, V, VII and XII. The prevalence of chromatolysis differed significantly between the diagnostic categories and was inversely related to the age of the animal. Duration of disease had a small but significant negative effect on the proportion of nuclei with chromatolytic neurons in chronic cases. The distribution of chromatolytic neurons is unlike that reported in any other equine or human disease; however, it appears to be equivalent to that in other animals with primary dysautonomias. EGS should be classified as a multisystem disease.
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The electrodiagnostic measurement of the thoracolaryngeal reflex (TLR) ('slap test') latency was compared to 5 other diagnostic techniques used for evaluation of laryngeal function, namely laryngeal muscle palpation, resting and immediately postexercise endoscopic examinations, and palpable and endoscopic responses to the TLR. Compared to resting endoscopy, the electrodiagnostic measurement of TLR latency was not found to be an accurate test for the evaluation of recurrent laryngeal neuropathy (RLN), nor was laryngeal muscle palpation or the endoscopic response to the TLR. Twenty-five (71%) of 35 Clydesdale horses examined were affected by RLN; 16 (46%) had mild, 5 (14%) moderate, 3 (9%) severe hemiparesis and 1 (3%) had total laryngeal paralysis. Within these 35 horses, physical traits such as height or neck length did not correlate with the incidence or severity of RLN. Ten control ponies showed no evidence of abnormal laryngeal function.
The effect of an ocular administration of the alpha-1 adrenergic agonist phenylephrine was studied in 23 cases of grass sickness and 12 control horses. In the horses with grass sickness there was a significantly greater mean increase in the size of the palpebral fissure, as measured by the change in the angle of the eyelashes to the head observed from a frontal view.
The parasympathetic terminal cardiac ganglia were examined in three normal horses and in five horses with grass sickness. Histopathological changes, consistent with those observed in other ganglia of horses with grass sickness, were identified in the terminal cardiac ganglia of the affected horses. A functional analysis of cardiac autonomic control by time domain analysis (TDA) of heart rate variability was applied to eight horses with grass sickness, and double-paired to 16 normal horses on the basis of their age, sex and breed, and the time of day at which the electrocardiographs were obtained. There were statistically significant differences between the normal and the affected horses in terms of the triangular index (P=0.01), a geometric method of TDA, the sNN100 index (P=0.009), a statistical method of TDA, and the R to R interval (P<0.0005). These results indicate that there is a pathological and functional parasympathetic decentralisation to the heart in equine grass sickness.
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 whole-mounts 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 precise appearance of ptosis due to lesions at different sites was investigated in experimental ponies. The angles of the eyelashes to the head was used as an objective measurement of ptosis after local anaesthesia of the sympathetic trunk or the palpebral nerve and the administration of an ocular alpha agonist or antagonist. It was shown that ptosis is not an inevitable consequence of palpebral nerve pathology, that ocular alpha antagonists can induce ptosis, and that alpha agonist eyedrops have an inconsistent effect on the equine pupil, but are consistent at reversing ptosis induced by sympathetic denervation in unsedated horses.
Three unusual cases of salivary gland enlargement and hypersialosis in the dog that responded to anticonvulsant therapy are reported. Presenting complaints included weight loss, hypersalivation, retching and vomiting of several weeks' duration. Two dogs were presented with enlarged painful mandibular salivary glands. The third dog exhibited bizarre behaviour (including jaw chattering) and developed enlarged painful mandibular salivary glands during hospitalisation. Fine needle aspirate cytology and biopsies from the enlarged salivary glands revealed no significant pathological changes. In one dog, an electroencephalogram revealed changes consistent with epilepsy. Hypersialism and salivary gland enlargement resolved completely during phenobarbital administration in all cases. Two dogs were successfully weaned off treatment six months after diagnosis. The remaining dog relapsed after eight months, but normalised with the addition of oral potassium bromide. It is hypothesised that the syndrome idiopathic hypersialosis may in fact be an unusual form of limbic epilepsy.
OBJECTIVE: To determine the distribution of nerve fibers containing calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), and intermediate neurofilaments in nasal mucosa of horses. ANIMALS: 6 horses without evidence of nasal disease. PROCEDURE: Full-thickness nasal tissue specimens were obtained from the rostral portion of the nasal septum at necropsy, and fluorescence immunohistochemistry was performed to assess mucosal distribution of nerve fibers. RESULTS: Nerve fibers with CGRP-like immunoreactivity (CGRP-Li) formed a dense subepithelial network, and a large number of fibers were found coursing between epithelial cells. Fibers with CGRP-Li were also associated with blood vessels and mucous glands. Fibers with SP-like immunoreactivity (SP-Li) had a similar distribution and density. In contrast, there were few fibers with VIP-like immunoreactivity. Fibers containing intermediate neurofilaments were prominent and appeared as large nerve fiber bundles mainly adjacent to the nasal septum but also close to mucous glands and within the lamina propria. Intermediate neurofilaments were also identified in single nerve fibers at all sites, but the density of fibers with intermediate neurofilaments did not match that of fibers with CGRP- or SP-Li. CONCLUSIONS: The density and distribution of nerve fibers containing SP- or CGRP-Li in nasal mucosa of horses was similar to that reported for other species. However, expression of VIP in nerve fibers was low. Antibodies against intermediate neurofilaments identified many nerve fibers in nasal mucosa of horses but did not appear to identify small diameter fibers expressing SP or VIP.
The interstitial cells of Cajal (ICC) are c-kit immunoreactive cells of the gastrointestinal tract which are suggested to have a role in the control of intestinal motility. Cells with c-kit immunoreactivity have not been previously described in the gastrointestinal tract of the horse. Immunoreactivity for c-kit was revealed using immunohistochemical labelling with an anti-c-kit polyclonal antibody. Sections of normal gastrointestinal tissue were examined from 13 anatomically defined sites from stomach to small colon taken from horses free from gastrointestinal disease. Three types of c-kit immunoreactive cells were identified: spindle-shaped cells in the region of the myenteric plexus, stellate or bipolar cells in the circular muscle layer, and round cells in the submucosa. The round cells were shown to be mast cells with the use of toluidine blue staining, whereas the other c-kit immunoreactive cells did not exhibit metachromasia and were classified as ICC. This study will serve as a basis for future pathological studies in the horse.
The autonomic innervation of the mammalian respiratory system is complex, and involves a wide variety of peptide and non-peptide neurotransmitters which will have an important role in normal laryngeal function and the response to disease. This innervation has been partially described in the horse airway and lung, but there is no information on the equine larynx. This paper describes the expression and distribution of nerve fibres immunoreactive for vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP) and the adrenergic enzymatic marker dopamine beta-hydroxylase (DBetaH) in the mucosa of the equine larynx. The overall relative density of nerve fibres immunoreactive for the different antigens was VIP>>CGRP>SP>>DBetaH. There were differences in the distribution of nerve fibre types, although each antigen was found in nerve fibres adjacent to blood vessels and mucous glands. VIP -like immunoreactivity (VIP -Li) was particularly extensive in association with mucous glands. SP - and CGRP -like immunoreactivity (SP -Li, CGRP -Li) were also seen close to the epithelium, with occasional nerve fibres coursing beneath and between the epithelial cells. Fragments of SP -Li and CGRP -Li fibres were also present in large nerve fibre bundles and ganglionic cell clusters, but not in the neurons themselves. The density of nerve fibres immunoreactive for DBetaH was very low and restricted to blood vessels and mucous glands. There was marked variation in the density of nerve fibres at the different sites, with the greatest density, particularly for VIP, over the arytenoid cartilage. Immunoreactive nerve fibres were less plentiful over the epiglottis, and the density of all types of nerve fibres was low over the cricoid cartilage. Overall VIP -Li nerve fibres were the most plentiful.
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Brainstem auditory evoked potentials (BAEPs) were recorded from 27 ponies. The peak and inter-peak (IP) latencies, V:I ratios and dispersal values were determined and the results from each category were compared with each other and with the authors' Thoroughbred BAEP data. Peak latencies were faster for ponies. The V:I ratios and dispersal values had similar characteristics in horses and ponies. In ponies there was a strong trend for IP latencies to be positively correlated with height, inter-aural distance and age. A positive relationship between I-V IP latency and inter-aural distance was confirmed in ponies as well as horses.
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OBJECTIVE: To determine the clinical outcome of horses treated for infection of the intertubuercular bursa (infectious bicipital bursitis). DESIGN: Retrospective analysis of case records. ANIMALS: Four horses referred for treatment of infectious bicipital bursitis. PROCEDURE: Medical records of horses that were severely lame on admission were reviewed. RESULTS: In 3 horses, palpation over the bicipital bursa as well as flexion and extension of the scapulohumeral joint were resented. Ultrasonography performed in 1 horse revealed that the bicipital bursa was large and that excessive amounts of fluid containing hyperechoic material were evident within the bicipital bursa. Two horses were treated by the administration of antimicrobial and nonsteroidal antiinflammatory drugs. Both remained lame and failed to resume their former activity. Two horses additionally were treated surgically by means of a partial synovectomy. Both resumed their former activity although a subtle lameness remained in 1 horse. CLINICAL IMPLICATIONS: Partial synovectomy may be useful in the treatment of horses with infectious bicipital bursitis.