[EAS] Gradient Detector

[pjk]

Subject:   Gradient Detector

Amidst my typical meditations, here is something astonishingly
different.  --PJK

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from
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 688 June 11, 2004  by Phillip F. Schewe, Ben Stein
                                                                	
A NEW CHEMOTAXIS ASSAY reveals nerve cells' surprising sensitivity.
A new method for studying the guidance (change in direction) of
neurons amid a sea of protein molecules shows how sensitive this
process is to the surrounding protein gradient.  Chemotaxis is the
process by which living cells sniff out their local environment and
act accordingly, which usually means moving or growing toward higher
concentrations of beneficial molecules.  In the case of neurons
removed from their natural setting and put down on a bed of collagen
gel in a dish, growth will follow the increasing gradient of
proteins in their vicinity, such as the nerve growth factor (NGF)
protein.  Neuronal growth, the way in which the long axon bodies of
a nerve cells wire themselves into a network, is of great interest
since this aids in knowing how brains form.  Now a team of
scientists at Georgetown University has developed a new method for
measuring the gradient of local proteins (which have been
fluorescently tagged) and the axon's response.  In this case the
neural cells come originally from a rat's brain.  The Georgetown
team of neuroscientists and physicists find that axon growth is
sensitive to gradients so small (0.1%) that they correspond to about
one additional molecule across the spatial extent of the axon's
"growth cone," the sensing device at the tip of the growing axon.
This is a remarkable feat considering that, at any one instant,
there are large statistical fluctuations in the 1000 or so NGF
molecules in the vicinity of the growth cone.  The researchers
suggest that axons may thus be "nature's most-sensitive gradient
detectors."  (Rosoff et al., Nature Neuroscicence, June 2004;
contact Jeffrey Urbach, urbach at physics.georgetown.edu, 202-687-6594;
or Geoffrey Goodhill, geoff at georgetown.edu)