Journal of Neuroscience, Vol 13, 2024-2032, Copyright © 1993 by Society for Neuroscience
Neurogenesis in adult canary telencephalon is independent of gonadal hormone levels
SD Brown, F Johnson and SW Bottjer
Department of Biology, University of Southern California, Los Angeles 90089-2520.
Neurons generated in adulthood are found throughout the canary
telencephalon. We are interested in the factors that control the rate of
proliferation of stem cells that give rise to these new neurons. The rate
of incorporation of newly generated neurons into vocal-control regions
varies seasonally. This difference could reflect a higher rate of
neurogenesis, a lower rate of cell death, or an altered migration. We
examined the incidence of thymidine-labeled cells in the telencephalic
ventricular zone of adult canaries as a function of variations in gonadal
hormone levels. Adult female canaries maintained on a short-day photoperiod
were anesthetized and gonadectomized. Four separate groups of birds
received systemic exposure to either testosterone, estradiol, a combination
of an anti-androgen and an inhibitor of estrogen synthesis, or nothing. All
birds were also implanted with an osmotic minipump that released
3H-thymidine for 3 d and were killed 4 or 7 d following the onset of
treatment. Analysis of autoradiograms revealed no differences between
groups in the incidence of labeling within the ventricular zone either at
the level of the anterior commissure or directly adjacent to the
vocal-control nucleus HVC (higher vocal center). These results suggest that
sex steroids do not regulate the rate of cell division in the ventricular
zone. Seasonal differences in the incorporation of labeled cells into HVC
may therefore be due to regulation of neurogenesis by photoperiodic factors
other than gonadal steroids or to some other cellular mechanism, such as
differential migration or survival of neurons.