New branch definitions and branch events at segments other than terminal segments improve the realism of the development of neuronal arbor.
Two recent improvements of the dendritic and axonal growth models are (1) the distinction between forking or main-daughter branch types and (2) the inclusion of branch events at intermediate segments.

The two branch types were observed in data obtained by Ger Ramakers' lab. In particular, forks in which the angles of both daughter segments at a branch are similarly different from the angle of the parent segment seem to occur almost exclusively at the very base of an arbor. The most prevalent type of branch is the main-daughter branch, in which a main segment continues with a slight deviation from the parent angle and one daughter segment veers away at angles up to 90 degrees.

TIme-lapse observations made in the Ramakers lab also showed that (rapid) growth of a terminal segment may be significantly delayed, which appears as if a new branch begins to grow (deep) within existing arbor. In terms of morphological statistics, this has the effect that the increasing number of terminal segments may involve the addition of fibre structure (and terminal segments) at distances more proximate to the cell body than the average radius of the arbor at that specific age. In order to accomodate these growth features that may affect spatially dependent synapse formation, simulated branching within the existing arbor was implemented by the possible conversion of a turn into a branch.

The results are shown in the following animation of a five day simulation, which focuses on a 200 by 200 micron region around a single neuron. A yellow circle appears during the animation and points out the development of a typical main-daughter branch. A cyan circle appears shortly thereafter to point out delayed branching (the conversion of what appeared to be a continuation node into a bifurcation).

figure: http://web.archive.org/web/20090106122138im_/http://rak.minduploading.org/nibr/main-daughter-and-turn-to-branch.gif

Created by randalk 
Last modified 2005-08-31 01:05 PM