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Abstract:
Visual inspection of neurons suggests that dendritic
orientation may be determined both by internal constraints (e.g.
membrane tension) and by external vector fields (e.g.
neurotrophic gradients). For example, basal dendrites of
pyramidal cells appear nicely fan-out. This regular orientation
is hard to justify completely with a general tendency to grow
straight, given the zigzags observed experimentally. Instead,
dendrites could (
A
) favor a fixed (``external'') direction, or (
B
) repel from their own soma. To investigate these possibilities
quantitatively, reconstructed hippocampal cells were subjected to
Bayesian analysis. The statistical model combined linearly
factors
A
and
B
, as well as the tendency to grow straight. For all
morphological classes,
B
was found to be significantly positive and consistently greater
than
A
. In addition, when dendrites were artificially re-oriented
according to this model, the resulting structures closely
resembled real morphologies. These results suggest that
somatodendritic repulsion may play a role in determining
dendritic orientation. Since hippocampal cells are very densely
packed and their dendritic trees highly overlap, the repulsion
must be cell specific. We discuss possible mechanisms underlying
such specificity.
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