k.p.collins at worldnet.att.net
Sun Nov 3 01:29:27 EST 2002
Age-related changes underlie switch in netrin-1 responsiveness as
growth cones advance along visual pathway.
Shewan D, Dwivedy A, Anderson R, Holt CE.
Department of Anatomy, University of Cambridge, Downing Street,
Cambridge CB2 3DY, UK.
Retinal axons are led out of the eye by netrin-1, an attractive
guidance cue which is secreted at the optic nerve head. In the optic
pathway, however, netrin-1 is expressed in areas that exclude retinal
axon growth. This suggests that axons may change in their
responsiveness to netrin-1 as they advance along the pathway. Indeed,
in our 'whole-pathway' preparation in Xenopus, a gradual change from
attraction to repulsion occurred as retinal axons emerged from
progressively distal points along the pathway. We also found that
axons that were aged in culture without pathway experience underwent
a similar change, which correlated with a decline in cyclic AMP
(cAMP) and netrin-1 receptor expression. Cyclic AMP elevators and
adenosine A2b receptor agonists rejuvenated the behavior of old
growth cones, causing them to regain attraction to netrin-1, whereas
antagonists caused young growth cones to be repelled. These findings
show that netrin-1 responsiveness is developmentally regulated and
suggest that intrinsic changes that lower cAMP levels underlie this
PMID: 12352982 [PubMed - indexed for MEDLINE]
© by someone other than me.
Here is an example of stuff that enters into the hierchical stuff
that I've been discussing - at the neruonal 'level'.
Also, since cAMP is part of fundamental metabolic functionality,
what's here is 'just' more activation-dependence.
There's more than one form of "backward propagation".
K. P. Collins
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