Cuntz H, Forstner F, Haag J, Borst A. The morphological identity of insect dendrites.
PLoS Comput Biol 2008;
4:e1000251. [PMID:
19112481 PMCID:
PMC2588660 DOI:
10.1371/journal.pcbi.1000251]
[Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2008] [Accepted: 11/12/2008] [Indexed: 11/19/2022] Open
Abstract
Dendrite morphology, a neuron's anatomical fingerprint, is a
neuroscientist's asset in unveiling organizational principles in the
brain. However, the genetic program encoding the morphological identity of a
single dendrite remains a mystery. In order to obtain a formal understanding of
dendritic branching, we studied distributions of morphological parameters in a
group of four individually identifiable neurons of the fly visual system. We
found that parameters relating to the branching topology were similar throughout
all cells. Only parameters relating to the area covered by the dendrite were
cell type specific. With these areas, artificial dendrites were grown based on
optimization principles minimizing the amount of wiring and maximizing synaptic
democracy. Although the same branching rule was used for all cells, this yielded
dendritic structures virtually indistinguishable from their real counterparts.
From these principles we derived a fully-automated model-based neuron
reconstruction procedure validating the artificial branching rule. In
conclusion, we suggest that the genetic program implementing neuronal branching
could be constant in all cells whereas the one responsible for the dendrite
spanning field should be cell specific.
Neural computation has been shown to be heavily dependent not only on the
connectivity of single neurons but also on their specific dendritic
shape—often used as a key feature for their classification. Still,
very little is known about the constraints determining a neuron's
morphological identity. In particular, one would like to understand what cells
with the same or similar function share anatomically, what renders them
different from others, and whether one can formalize this difference
objectively. A large number of approaches have been proposed, trying to put
dendritic morphology in a parametric frame. A central problem lies in the wide
variety and variability of dendritic branching and function even within one
narrow cell class. We addressed this problem by investigating functionally and
anatomically highly conserved neurons in the fly brain, where each neuron can
easily be individually identified in different animals. Our analysis shows that
the pattern of dendritic branching is not unique in any particular cell, only
the features of the area that the dendrites cover allow a clear classification.
This leads to the conclusion that all fly dendrites share the same growth
program but a neuron's dendritic field shape, its “anatomical
receptive field”, is key to its specific identity.
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