The Interscutularis Muscle Connectome

The complete connectional map (connectome) of a neural circuit is essential for understanding its structure and function. Such maps have only been
obtained in Caenorhabditis elegans. As an attempt at solving mammalian circuits, the authors reconstructed the connectomes of six interscutularis
muscles from adult transgenic mice expressing fluorescent proteins in all motor axons. The reconstruction revealed several organizational principles
of the neuromuscular circuit.


First, the connectomes demonstrate the anatomical basis of the graded tensions in the size principle. Second, they
reveal a robust quantitative relationship between axonal caliber, length, and synapse number. Third, they permit a direct comparison of the same
neuron on the left and right sides of the same vertebrate animal, and reveal significant structural variations among such neurons, which contrast with
the stereotypy of identified neurons in invertebrates.


Finally, the wiring length of axons is often longer than necessary, contrary to the widely held
view that neural wiring length should be minimized.


These results show that mammalian muscle function is implemented with a variety of wiring diagrams
that share certain global features but differ substantially in anatomical form. This variability may arise from the dominant role of synaptic
competition in establishing the final circuit.



Citation:
" The interscutularis muscle connectome."
Lu J, Tapia JC, White OL, Lichtman JW (2009)
PLoS Biol 7(2): e1000032.

doi:10.1371/journal.pbio.1000032

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