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Article 5476 of comp.ai.philosophy:
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>From: bill@NSMA.AriZonA.EdU (Bill Skaggs)
Newsgroups: comp.ai.philosophy
Subject: Re: what we know about neurons
Message-ID: <1992May8.051322.28285@organpipe.uug.arizona.edu>
Date: 8 May 92 05:13:22 GMT
References: <1992Apr9.174840.3407@organpipe.uug.arizona.edu> <5674@mtecv2.mty.itesm.mx> <2@tdatirv.UUCP> <1992May5.125445.22000@hobbes.kzoo.edu> <17@tdatirv.UUCP>
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Reply-To: bill@NSMA.AriZonA.EdU (Bill Skaggs)
Organization: Center for Neural Systems, Memory, and Aging
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Jamie R. McCarthy:
>I read once that, although we know a lot about single neurons, we are
>quite ignorant of how two neurons connect.  It was asserted that the
>Golgi stain method is our only means of viewing cells, and that it only
>affects, randomly, one cell in a thousand.  Thus, we've never seen two
>neurons next to each other, so we don't really know how they interact.
>
>Was this written before the electron microscope?  Please excuse my
>ignorance of biology...

  This hasn't been true for more than a century:  even Ramon y Cajal,
in his first studies using the Golgi technique, saw many cases of
neurons touching one another.  He couldn't actually resolve the
synaptic contacts (that wasn't possible until electron microscopy
came into use), but he was sure they existed.

  EM is still the only way to be really *sure* that cells contact
each other, but there are now quite a variety of ways of viewing
neurons.  The Golgi method is probably used less commonly than
some of the others, particularly intracellular injection of dyes
such as Horseradish Peroxidase (HRP) or Lucifer Yellow.

  Actually, connectivity is probably one of the things we know
*most* about, especially connectivity between widely separated
parts of the brain.  Except for a few relatively simple structures
like the cerebellum, we still know pretty little about local
connectivity.

Stanley Friesen:
>Well, it is true that Golgi staining is the primary way of staining neurons
>for optical viewing, but we have many other ways of studying neuronal
>connectivity.  One major method involves retrograde degeneration - the axons
>of a killed cell die off, so one can see which connections disappear, and
>so estimate connectivity.

  Much of what we know about connectivity was originally learned using
the retrograde degeneration technique, but it is hardly ever used
nowadays, because it is technically very difficult and also not
nearly as sensitive as other methods.

SF:
>In fact it is at the level of connectivity that we have the most to learn about
>neuronal function.  That along with certain aspects of learning.

  I would say the majority of neuroscientists nowadays are working
at the molecular level, studying the interactions of proteins,
lipids, and genes in nerve cells.  But the fact is we have a hell
of a lot to learn about almost every aspect of neuronal function.
Particularly about learning:  we have only the barest glimmer of
understanding of the mechanisms involved.

	-- Bill


