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Regeneration of neurons [was Re: Extending the lifespan...]

William Calvin wcalvin at hardy.u.washington.edu
Wed May 6 12:06:03 EST 1992

allens at yang.earlham.edu (Allen Smith) writes:

>> And no, too, regarding much higher function that depends on memory that is
>> help in a pattern of cell connections.  The reason that neurons don't
>> divide during life is probably that it would destroy the established
>> pattern of connections with thousands of other neurons, that constitutes
>> the memory engram.
>        It does seem that actual neuronal division wouldn't be good (for
>the reasons that you mention). The interesting possiblity, therefore, is
>to persuade the neuronal support cells (which can divide, of course;
>they're what produce brain tumors) to divide and have one of the division
>products go back to the state before the differentation between neuronal
>precursor and support precursor, and take the path not taken.
>        -Allen

The problem is that neural development is a long and complicated process,
with much overproduction of cells and then killing off extras, with much
disconnecting of synapses and withdrawal of axons (corpus callosum in
monkey has 200 million axons at birth; within six months, the count is
down to 45 million, a 70% loss).  Even if we understood the process as
well as DNA-to-RNA-to-proteins, we would still have the problem of getting
the production staged correctly (and just consider how complicated it is
to do peptide sequencing in vivo).  The best we've been able to do, even
in the simpler case of spinal cord, is to produce some tubes to guide
long-tract growth, to help the sprouts in the right direction; left to
themselves, they get lost and give up.

    William H. Calvin   WCalvin at U.Washington.edu
    University of Washington  NJ-15
    Seattle, Washington 98195 FAX:1-206-720-1989

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