APOPTOSIS AS A REGULATOR OF CELL-PROLIFERATION IN THE CENTRAL POSTERIOR PREPACEMAKER NUCLEUS OF ADULT GYMNOTIFORM FISH, APTERONOTUS-LEPTORHYNCHUS/

Like many species of teleost fish, the gymnotiform Apteronotus leptorh ynchus displays a high degree of proliferative activity in a large num ber of brain regions during adulthood. One of these regions is the cen tral posterior/prepacemaker nucleus (CP/PPn) in the diencephalon. By a pplying in situ techniques for the detection of DNA fragmentation, a f eature characteristic of apoptotic cells, we show in the present study that the high proliferative activity in the CP/PPn is counterbalanced by programmed cell death. Most of the apoptotic events occur in the v entricular and subventricular zones of this thalamic complex, where th e generation of the cells and their differentiation into neurons take place. The demonstration of apoptosis in the CP/PPn provides strong ev idence against the hypothesis that animals in which neurogenesis conti nues beyond embryonic stages of development lack cell death.