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The Journal of Neuroscience, January 15, 2000, 20(2):854-861
Breeding Conditions Induce Rapid and Sequential Growth in Adult
Avian Song Control Circuits: A Model of Seasonal Plasticity in the
Brain
Anthony D.
Tramontin1,
Vesta N.
Hartman3, and
Eliot A.
Brenowitz1, 2, 4
Departments of 1 Zoology, 2 Psychology,
3 The Graduate Program in Neurobiology and Behavior, and
4 The Virginia Merrill Bloedel Hearing Research Center,
University of Washington, Seattle, Washington 98195
In adult songbirds, seasonal changes in photoperiod and circulating
testosterone (T) stimulate structural changes within the neural song
control circuitry. The mechanisms that control this natural plasticity
are poorly understood. To determine how quickly and in what sequence
the song nuclei respond to changing daylength and circulating T, we
captured 18 adult male white-crowned sparrows and kept them on short
days for 12 weeks. We killed five of these birds and exposed the rest
to long days (LD) and elevated T. We killed these birds either 7 or
20 d after LD + T exposure. We measured song nuclei volumes and
cellular attributes, the mass of the vocal production organ (the
syrinx), and song behavior. The neostriatal song control nucleus HVC
(also known as "high vocal center"), added 50,000 neurons and
increased in size within 7 d of exposure to LD + T. Efferent
targets of HVC, the robust nucleus of the archistriatum (RA), and area
X of the parolfactory lobe grew more slowly and were not significantly
larger until day 20 of the study. The tracheosyringeal portion of the
hypoglossal nucleus (nXIIts), which receives projections from RA and
normally grows in response to seasonal cues, did not grow over the time course of this study. Syringeal mass increased within 7 d of LD + T treatment. The anatomical changes in the brain were accompanied by
behavioral changes in song production. On day 7 when the song circuitry
was incompletely developed, male sparrows sang less stereotyped songs
than males at day 20 with more completely developed song circuits.
These results suggest that the song circuitry responds rapidly and
sequentially to breeding-typical conditions (long days and elevated T),
and that song stereotypy increases as nuclei within this circuitry grow.
Key words:
plasticity; season; songbird; song system; testosterone; white-crowned sparrow
Copyright © 2000 Society for Neuroscience 0270-6474/00/202854-08$05.00/0
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