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- S. Schönknecht,
M. Scholz, C. Duch, J. Evers, and K. Obermayer. Multi compartment model of
development changes in dendritic shape during postembryonic motorneuron
development.
.
In Proceedings of the 29th Göttingen Neurobiology Conference,
2003.
(FTP PDF, 4 kb)
During metamorphosis of the moth Manduca sexta the individually
identified motoneuron MN5 is remodelled from a slow larval crawling into a
fast adult flight neuron. A fivefold lower input resistance, a higher firing
threshold, and an increase of voltage activated potassium current result in a
much lower excitability of the adult MN5 as compared to the larval MN5 [Duch,
Levine; 2000], thus meeting the newly acquired behavioural requirements. This
postembryonic change in membrane properties and function is accompanied by
drastic changes in dendritic architecture. Regression of larval dendrites is
followed by growth and sprouting of new adult dendrites during metamorphosis
[Libersat, Duch; 2002]. In many neurons processing of synaptic input and
excitability are strongly dependent upon dendritic shape as demonstrated by
studies that used multi compartment models. We use the well defined changes
in membrane properties, dendritic shape, and behavioural function of MN5 to
further address the question how developmental changes in dendritic shape
affect dendritic processing and excitability to accommodate changing
behavioural requirements during postembryonic life. Our model results from
3-D reconstructions of MN5 from confocal image stacks. We extract a skeleton
and the diameters of the MN5 by means of our reconstruction method [Schmitt
et. al, 2003]. These metric data are imported into the simulation environment
GENESIS by means of an automated parser. Currently, the simulations focus on
adjustments and validations of our electrophysiological model in comparison
to intracellular recordings in the cell body of MN5. Input resistance, the
shape of passively conducted action potentials, resting membrane potential,
firing threshold and time constant have been determined by single electrode
current clamp recordings in situ. Under assumption of unaltered passive
membrane properties, the length constant (lambda) can be calculated by means
of the model. In parallel we aim to determine lambda by dual electrode
recordings. We present simulation results concerning the following questions:
First: In how far does an improved geometric model optimize the model,
depending on various integration methods? Second: In what range do deviations
of electrophysiological parameters influence the simulation results? Third:
How does dendritic branch order affect summation of synaptic input with
respect to the assumed site of spike initiation? Fourth: How does dendritic
branch addition during development affect the summation of synaptic input in
branches of given orders? Our model provides the possibility of synaptic
inputs to specific branch orders. In the long term we aim to understand to
what extend changes in dendritic shape as occurring during normal
postembryonic development may contribute to alterations in neuronal function
that meet changing behavioural requirements.
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