Modelling gap junction-coupled networks of olfactory bulb mitral cells

Abstract

Summary of Thesis: The olfactory bulb forms the first level of input integration for olfactory receptor neurons that receive stimuli from odorant molecules in the nose. The olfactory bulb is multi channel in nature, with each channel containing its own populations of mitral cells. These channels each handle the input from neurons expressing a single type of olfactory receptor protein tuned to a unique range of odorant structures. I have constructed a mitral cell gap-junction network model with morphologically accurate mitral cells to study the behaviour of mitral cells in a channel population. The passive parameters of each of the mitral cells were determined by fitting to in vitro recordings. Sodium and potassium channels were added to the mitral cells to give the ability to generate action potentials. Gap-junctions were placed in the apical dendrite tufts of the mitral cells and their conductance adjusted to give a coupling ratio between mitral cells consistent with experimental findings. Firing was induced with twenty current injections randomly located in the apical dendrite tuft of two of the mitral cells, mimicking the multiple inputs from the olfactory receptor neurons. A protocol was used to promote an initial asynchrony in firing which was transmitted across the gap-junctions to all six mitral cells. I found that the mitral cell population would overcome this asynchrony, rapidly tending to synchronous firing. Adding calcium and calcium dependent potassium channels to the mitral cells produced burst firing patterns that were different for each of the cells. The gap-junctions did not have enough influence to overcome the asynchrony of the different burst firing patterns. The addition of calcium concentration threshold dependant glutamate release and AMPA auto receptors to the apical dendrite tuft of each mitral cell allowed the burst firing to promote self propagating synchronised firing after an initial period of asynchrony