In this study the functional integrity of relay neurones and their afferent input from optic tract fibres was monitored in the scrapie-infected dLGN throughout the incubation period. The aim of this study was to elucidate the mechanisms of scrapie-associated dysfunction at the level of the neuronal membrane. The properties of murine dLGN cells have not been characterised; a study of the membrane properties of these cells was carried out in order to ascertain if they were similar to rat and guinea-pig dLGN relay cells, and thus if results of the scrapie investigation could be interpreted in terms of the available literature on relay cell physiology in these species. The technique of intracellular recording from brain slices was used to evaluate the properties of dLGN relay cells in untreated (normal), normal brain inoculated (control) and scrapie-inoculated mice. The inoculated mice received an intraocular injection of either ME7 scrapie-infected or normal brain homogenate and recordings were made from coronal brain slice preparations of the dLGN at approximately 28 day intervals from 60 days post-inoculation. The incubation period in this model was approximately 270 days; two experimental series of inoculated mice were studied. Basic membrane properties (resting membrane potential, action potential threshold, input resistance and time constant), properties of averaged action potential shapes, the integrity of the synaptic response evoked by afferent optic tract stimulation and the membrane responses to current injection were studied in normal, control and scrapie-inoculated mice. In addition the morphology of cells in the control and scrapie-inoculated mice was monitored by iontophoresis of dye via the recording electrode. The study of normal mice demonstrated that relay neurones in the dLGN exhibited membrane response properties and responses to optic tract stimulation typical of those in the rat and guinea-pig. The basic membrane and action potential properties quantified were also similar to published studies. Significant correlations were found between: the time constant and input resistance; the after-hyperpolarisation (AHP) amplitude and spike threshold; spike amplitude and spike threshold. In terms of both their basic membrane and action potential properties murine dLGN relay cells constituted a homogeneous population. Both a fast and slow AHP followed the action potentials in murine dLGN relay cells; the slow AHP was apamin-sensitive indicating that it was mediated by the calcium-activated potassium conductance, I<SUB>AHP. </SUB>This conductance appeared to have a role in regulating the rate of action potential discharge. This study demonstrated that murine dLGN relay cells function as a homogenous population and possess similar properties to rat and guinea-pig dLGN relay cells. This is the first report of the conductance I<SUB>AHP</SUB> in dLGN relay cells.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:641663 |
| Date | January 1996 |
| Creators | Black, Catherine J. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/20752 |
Page generated in 0.0017 seconds