Journal of Neuroscience, Vol 8, 2869-2874, Copyright © 1988 by Society for Neuroscience
Sex and regional differences in the incorporation of neurons born during song learning in zebra finches
EJ Nordeen and KW Nordeen
Department of Psychology, University of Rochester, New York 14627.
In zebra finches only males sing, and several nuclei controlling song
contain more neurons in adult males than in females. The ontogeny of sex
differences in neuron number differs across song regions and overlaps with
song learning in males. We examined the development of neuron number in
several song regions in both sexes. We then determined whether neurons are
born and incorporated into song nuclei as sex differences in neuron number
emerge, and whether sex or regional differences in the insertion of such
neurons may account for differences in the development of these areas.
Males add neurons to hyperstriatum ventralis pars caudalis (HVc) and Area X
between 20 and 55 d of age. In females there is no change in HVc neuron
number during this time, and Area X never appears as a distinct nucleus. In
both sexes, 3H-thymidine administration between 20 and 30 d results in
neuronal labeling at 55 d in HVc and the region of Area X. However, in
these areas the incidence of labeled neurons is higher in males than in
females. In contrast to HVc and Area X, sex differences in neuron number in
the robustus nucleus of the archistriatum (RA) and the magnocellular
nucleus of the neostriatum (MAN) emerge because males retain neurons that
are lost in females between 20 and 55 d of age. Accordingly, RA and MAN
neurons are not labeled following 3H-thymidine administration between 20
and 30 d of age. These data indicate that sex and regional differences in
the ontogeny of song nuclei are related to differences in the incorporation
of neurons born during song learning.
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