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may be able to induce production of GS in a certain number
of glia as well as a large number of neurons could. This
possibility is compounded by the fact that there are many
different types of neurons in the optic tectum (LaVail and
Cowan, 1971a) and it is not known which types are capable
of GS induction. Maybe the small percentage of A2B5(-)
neurons that were in the purified cells were the neurons
that induced GS. Another possible explanation is that
neurons were recruited in the neuron-depleted purified
cells in a rapid manner so that they could interact with
the glia to produce GS. This would have to have been within
about a day as was determined by the isolation of cells in
methyl cellulose. If the appearance of A2B5 antigen on cell
surfaces was an indication of commitment to becoming a
neuron as is suggested then the ability to induce GS may
also have occured rapidly as did the expression of A2B5
antigen. However, this hypothetical change was not
sufficient to ensure survival of cells on polyornithine.
It is also worth mentioning that levels of GS produced
in aggregate cultures made from cells that were isolated in
methylcellulose were identical to levels produced by
immeadiately reaggregated dissociated cells. This is
surprising since it was shown that a much greater number
of A2B5(+) cells existed initially in cells from the
methylcellulose (75%) than in immeadiately reaggregated
cells (50%). So either the number of A2B5(+) cells has