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dc.contributor.authorMurray, Alisonen
dc.date.accessioned2018-05-14T10:14:50Z
dc.date.available2018-05-14T10:14:50Z
dc.date.issued1996en
dc.identifier.urihttp://hdl.handle.net/1842/29902
dc.description.abstracten
dc.description.abstractThis thesis describes investigations of small intestinal motility in horses with and without equine grass sickness using an in vitro technique. Equine grass sickness is a disease of horses of unknown aetiology, characterised by dysfunction of the autonomic nervous system, primarily affecting the alimentary tract. Examination of autonomic ganglia taken from horses affected with grass sickness shows evidence of neuronal degeneration and ultimately depletion of cell numbers.en
dc.description.abstractThe in vitro technique implemented used strips of intestinal smooth muscle cut parallel to the longitudinal muscle layer from the duodenum and ileum. Tissue was taken from control horses and those affected with the three clinical forms of grass sickness (acute [AGS], subacute [SAGS] and chronic grass sickness [CGS]). Motility patterns were measured isometrically using strain gauge transducers and recorded onto a Washington ink writing oscillograph. Contraction rate and amplitude, alterations in tone (baseline) and the latency before a response to pharmacological agents were recorded.en
dc.description.abstractThe characteristics of the background contractions were established. In the control group the duodenal preparations had a significantly higher contractile rate than ileal preparations (P<0.05). There was no significant difference in contractile amplitude between the two regions. The contractile rate was reduced in grass sickness cases, although not always significantly. The effect of storage for 24 hours at 4"C was investigated to determine whether stored control tissue would subsequently behave like fresh grass sickness tissue: it was concluded that this was not the case.en
dc.description.abstractPhysostigmine was used to establish the viability of enteric cholinergic neurones and to test their capacity to release endogenous acetylcholine. All muscle strips from both control horses and those affected with grass sickness showed significant increases in the rate of contractions following physostigmine addition (P<0.05 or less). The latency before a response to physostigmine in the AGS and SAGS groups was significantly larger than for the control groups in both regions of the gut (PcO.OOl for duodenal tissue, P<0.05 for ileal tissue). The effect of storage on responses to physostigmine confirmed that neuronal cell death takes place during this iii storage period. Grass sickness tissue could no longer produce a significant increase in contractile rate following physostigmine. Dose response curves to bethanecol were constructed for control, AGS and CGS tissue. For the AGS group there was a leftward shift of the dose response curve and a reduced ED50 value, which suggested that the tissue has become supersensitive (denervation hypersensitivity). However, there were no significant differences between the tissue sensitivity of the CGS and the control groups.en
dc.description.abstractCisapride is a prokinetic drug which has been used with some clinical success in the treatment of selected chronic grass sickness cases. Experiments using cisapride indicated there was an increase in the contractile rate in control and CGS duodenal muscle strips (P<0.06) and in control, AGS and CGS groups in ileal regions (P<0.06). Cisapride also caused an increase in the amplitude of contractions in ileal muscle strips taken from control horses (P<0.06).en
dc.description.abstractIn agreement with other workers, it was found that in vitro equine small intestine contracts oa addition of noradrenaline or adrenaline. This contractile response was found to be due to excitatory a2 receptors on the smooth muscle membrane. Grass sickness affected tissue responded similarly to control tissue in the duodenal region, however, in certain AGS and SAGS cases no contractile response to noradrenaline could be achieved until tissue was pretreated with the (3 antagonist propranolol. As cold storage had no significant effect on the contractile response to noradrenaline it would suggest the response was independent of nervous elementsen
dc.description.abstractA subjective histological scoring method was applied on sections of small intestine adjacent to those used in pharmacological experiments, to investigate neuronal cell number, size and the proportion of abnormal cells in the myenteric and submucous plexuses. There was a significantly lower score for neuronal cell number for the AGS and CGS groups compared with control values (P<0.05). The evidence suggested that in CGS cases the largest enteric neurones were preferentially affected by grass sickness (P<0.05). In the ileal AGS group, the proportion of abnormal cells was significantly greater than both the control and CGS ileal groups (P<0.05). In the duodenum there was no significant difference between the proportion of abnormal cells between the AGS and CGS groups, although they were both awarded significantly higher scores than the control group (P<0.05).en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2018 Block 18en
dc.relation.isreferencedbyAlready catalogueden
dc.titleIn Vitro small intestinal motility in horses with and without equine grass sicknessen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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