Neurogenesis

[kenneth Collins]

hi Brian, Thank You for posting this excellent 'review'.

i hope my comments, below, will be received as adding 'light'.

Brian Scott wrote:

>[...]

> Neurogenesis in adult animals had been reported as far back as 30 years
> ago by Joseph Altman and others, but until fairly recently the study of
> adult neurogenesis has been pretty slow.  In the last few years though
> things have really exploded.  The evidence for adult neurogenesis is
> pretty solid in rodents and birds

with respect to which (and probably with respect to all of the Genesis
of the current neural-genesis work), Fernando Nottebahm Deserves the
=main= credit. in the face of what was, Nottebahm's efforts were
Truly-Heroic.

>, and there are lots of examples now in
> primates and many other mammals.  Some of the early primate work failed
> to find convincing evidence of adult neurogenesis.  Since this work was
> produced by a big guy (Rakic) in the anatomy field, it was generally
> believed that primates were the exception.  Recent work by Gould and
> Gage's people as well as Rakic have now demonstrated adult neurogenesis
> in several primate species.  It had been said that the production of new
> neurons in adulthood would disrupt existing circuitry and therefore
> memory, and this is why neurogenesis in higher animals stops after
> development.  [Elizabeth Gould is now suggesting that adult neurogenesis
> may actually be important for certain types of memory.]

the question of 'disruption' is only correlated with 'transplant'
methodologies.

neural genesis is =Necessarily= governed by the same mechanisms that
govern all non-neural-genesis trophic dynamics, so, except in instances
of organic damage (disease & mechanical lesions) it's flat-out
impossible for neural genesis to 'disrupt' anything.

> 
> Kempermann and Gage used essentially the same techniques from the animal
> work to show neurogenesis in the hippocampus of adult cancer patients
> ranging in age from 30s to 70s I think.  It's pretty convincing to me
> but there are still criticisms with respect to the BrdU technique and
> whether it's really labelling new cells.

differentiation with respect to disease processes is one of those
Necessary things.

cheers, Brian, ken (K. P. Collins)

>  It's the same criticism of the
> technique since it was invented. Maybe the BrdU is being incorporated
> into dying or injured cells that manage to survive. Some have said that
> maybe this (neurogenesis) is just a phenomenon associated with cancer or
> its treatment.  There's at least one paper I know of since then that
> looked for a marker of cell division in tissue taken from epileptics
> that claimed there was no evidence of a subgranular proliferative
> zone...where the neurogenesis is supposed to occur.  I don't think his
> technique was sensitive enough though.  Anyway, besides the hippocampus
> there's also evidence for neural stem cells which may be generating
> neurons around the ventricles.  I'm less familiar with this though.
> Gould recently reported neurogenesis originating around the ventricles
> and sending neurons to the association cortex of monkeys.  Maybe this is
> happening in humans too.
> 
> With respect to the functionality of these cells, they look like the
> other cells nearby and send projections to the same targets and express
> the same marker proteins.  There is evidence of synapses on them too.
> Until someone can actually patch-clamp from a cell which was definately
> born in adulthood, there will always be those that question whether they
> are functional or not.  In animals, their production is very tightly
> regulated by adrenal hormones and probably by input to the dentate
> gyrus.  It's very likely they're being used for something.
> 
> --
> Brian Scott           |     Institute of Medical Science &
> brians at interlog.com   |  Bloorview Epilepsy Research Programme
>                       |        University of Toronto
>                       |           Toronto, Canada