Journal of Neuroscience, Vol 14, 6532-6543, Copyright © 1994 by Society for Neuroscience
Waiting periods versus early innervation: the development of axonal connections in the zebra finch song system
R Mooney and M Rao
Division of Biology, California Institute of Technology, Pasadena 91125.
This study examines the development of two neural pathways within the zebra
finch forebrain that function respectively in the juvenile acquisition and
the adult production of learned song. In the adult male zebra finch
forebrain, the song nuclei L-MAN and HVc both innervate nucleus RA; L-MAN
plays a crucial role in juvenile song acquisition but, unlike HVc and RA,
is not essential for adult song production. Previous studies have shown
that HVc axons arrive at the dorsal border of RA as early as posthatch day
15 (day 15), and only enter the male RA after days 25-30, but never enter
the female RA. The present study examines the development of axonal
projections from L-MAN to RA and finds that, in contrast to HVc axons,
L-MAN terminals are present within the male and female RA by day 15, and
persist there throughout adult life. Unlike RA-projecting HVc neurons, HVc
neurons projecting to area X innervate this target by day 20. Like L-MAN,
area X plays a transient role in song acquisition. These results suggest
that in the zebra finch forebrain, neural pathways essential to juvenile
song learning develop before those needed for adult song production.