matthew_avison at email.msn.com Thu Aug 6 06:34:07 EST 1998 Some
tissues that constantly proliferate (like skin for example) do
so because the tissues contain stem cells. These cells are
constantly dividing and producing daughters who the
differentiate into the main cells of the tissue (e.g. skin
cells). Such tissues usually undergo a constant cell death at
their surface (e.g. skin cells die at the surface and are shed)
so the stem cells are essential to stop the tissue waring away,
providing a constant supply of new cells. The brain as a tissue
is very different. It is not designed to cope with constant
waring away of differentiated cells like the skin is. Therefore
there are very few neuronal stem cells to provide new cells to
replace ones that do die. Hence eventually the brain starts
falling apart. For most people, however, they are dead before
this really happens. One of the holy grails of neuroscience is
to try and get neurones to de-differentiate into stem cells,
thus allowing a source of proliferation