BCL-2 PROTEIN AS A MARKER OF NEURONAL IMMATURITY IN POSTNATAL PRIMATEBRAIN

The distribution of neurons expressing immunoreactivity for the protei n Bcl-2 was studied in the brain of squirrel monkeys (Saimiri sciureus ) of various ages, Several subsets of small and intensely immunoreacti ve neurons displaying an immature appearance were disclosed in the amy gdala and piriform cortex, The piriform cortex exhibited clusters of v arious forms in which Bcl-2+ neurons appeared linked to one another by their own neurites, The subventricular zone, which is known to harbor the largest population of rapidly and constitutively proliferating ce lls in the adult rat brain, was intensely stained, particularly at the basis of the lateral ventricle, A long and dorsoventrally oriented Bc l-2 fiber fascicle was seen to emerge from the subventricular zone, to gether with numerous Bcl-2+ cells that formed a densely packed column directed at the olfactory tubercle, in adult and aged monkeys, the sma lt and intensely labeled neurons were progressively replaced by larger and more weakly stained neurons in the amygdala and piriform cortex. in contrast, Bcl-2 immunostaining did not change with age in the subve ntricular zone and olfactory tubercle, the islands of Calleja of which were markedly enriched with Bcl-2, The dentate gyrus contained only a few layers of intensely labeled granule cells in juvenile monkeys, bu t the number of these layers increased markedly in adult and aged monk eys, These findings suggest that Bcl-2 can serve as a marker of both p roliferating and differentiating neurons and indicate that such immatu re neurons may be much more widespread than previously thought in post natal primate brain.