The Journal of Neuroscience, April 1, 2001, 21(7):2320-2329
Afferent Input Is Necessary for Seasonal Growth and Maintenance
of Adult Avian Song Control Circuits
Eliot A.
Brenowitz and
Karin
Lent
Departments of Psychology and Zoology and Virginia Merrill Bloedel
Hearing Research Center, University of Washington, Seattle, Washington
98195-1525
The neural circuits that regulate song behavior in adult songbirds
undergo pronounced seasonal changes in morphology, primarily in
response to changes in plasma testosterone (T). Most song nuclei have T
receptors. We asked whether seasonal growth and maintenance of nuclei
within these circuits are direct responses to the effects of T or its
metabolites or are mediated indirectly via the effects of T on afferent
nuclei. Photosensitive white-crowned sparrows were exposed to one of
three treatments. (1) The neostriatal nucleus HVc (also known as
the "high vocal center") was lesioned unilaterally, and the birds
were exposed to long-day (LD) photoperiods and breeding levels of T for
30 d. (2) Birds were exposed to LD plus T (LD+T) for 30 d;
then HVc was lesioned, and the birds were killed after an additional
30 d exposure to LD+T. (3) HVc was lesioned, and the sparrows were
housed on short-day (SD) photoperiods in the absence of T treatment for
30 d. In both LD+T groups, the direct efferent targets of HVc, the
robust nucleus of the archistriatum (RA) and area X, were
smaller ipsilateral to the lesion. The lesion did not prevent growth of
the hypoglossal motor nucleus, which does not receive direct afferent
input from HVc. RA and area X were also smaller ipsilateral to the
lesion in the SD birds. These results indicate that afferent input is
required both for the growth of adult song circuits in response to
typical breeding photoperiod and hormone conditions and for the
maintenance of efferent nuclei in either their regressed or enlarged states.
Key words:
afferent; bird; birdsong; plasticity; season; songbird; song; song system; testosterone; trophic; white-crowned sparrow
Copyright © 2001 Society for Neuroscience 0270-6474/01/2172320-10$05.00/0
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