Modelling the synaptic effects in olfactory bulb mitral cells

Written by Szilágyi Tibor, Metz Júlia, Orbán-Kis Károly

We have studied the influence of the three dimensional structure of the dendrites of the olfactory bulb mitral cells on the information processing performed by these cells. Compartmental models were implemented in the Neuron simulation environment. The mitral cell model published by Bhalla and Bower in 1993 was complemented by combined AMPA/NMDA type excitatory synapses placed on the glomerular tuft and GABA-A type inhibitory synapses on the secondary dendrites. On synaptic input, the glomerulus generated large Ca-spikes, and showed to be overexcitable. Increasing the density of potassium channels decreased the excitability but the action potentials were always generated first in the glomerulus and later in the soma. The somatic action potentials initiated regenerative action potentials in the secondary dendrites, suggesting that lateral inhibition mediated by granule cells can exist between distant glomeruli. Feed-back inhibition received from granule cells could preclude the propagation of excitation in that branch, but did not affect other secondary dendrites. In conclusion, there are important interactions between excitatory and inhibitory potentials in the modelled dendrites which cannot be reproduced in models with simplified morphology.

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