On the other hand, the observation that reactive
oxygen species are produced during neurotrophin withdrawal-induced
PCD179 raises the possibility that release of cytochrome c to the cytosol is
involved in caspase activation in this setting. Although the effects of Bcl-2
on cytochrome c release and neurotrophin withdrawal-induced apoptosis
(see Section 6.2) are consistent with this possibility, it remains to be determined
how (or even whether) cytochrome c release is induced after neurotrophin
withdrawal.