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The Journal of Neurophysiology Vol. 82 No. 5 November 1999, pp. 2221-2234
Copyright ©1999 by the American Physiological Society
Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710
White, Stephanie A.,
Frederick S. Livingston, and
Richard Mooney.
Androgens Modulate NMDA Receptor-Mediated EPSCs in the Zebra
Finch Song System. J. Neurophysiol. 82: 2221-2234, 1999. Androgens potently regulate the development of learned
vocalizations of songbirds. We sought to determine whether one action of androgens is to functionally modulate the development of synaptic transmission in two brain nuclei, the lateral part of the magnocellular nucleus of the anterior neostriatum (LMAN) and the robust nucleus of
the archistriatum (RA), that are critical for song learning and
production. We focused on
N-methyl-D-aspartate-excitatory postsynaptic currents (NMDA-EPSCs), because NMDA receptor activity in
LMAN is crucial to song learning, and because the LMAN synapses onto RA
neurons are almost entirely mediated by NMDA receptors. Whole cell
recordings from in vitro brain slice preparations revealed that the
time course of NMDA-EPSCs was developmentally regulated in RA, as had
been shown previously for LMAN. Specifically, in both nuclei,
NMDA-EPSCs become faster over development. We found that this
developmental transition can be modulated by androgens, because
testosterone treatment of young animals caused NMDA-EPSCs in LMAN and
RA to become prematurely fast. These androgen-induced effects were
limited to fledgling and juvenile periods and were spatially
restricted, in that androgens did not accelerate developmental changes
in NMDA-EPSCs recorded in a nonsong area, the Wulst. To determine
whether androgens had additional effects on LMAN or RA neurons, we
examined several other physiological and morphological parameters. In
LMAN, testosterone affected
-amino-3-hydroxy-5-methyl-4-isoxazoleproprianate-EPSC (AMPA-EPSC)
decay times and the ratio of peak synaptic glutamate to AMPA
currents, as well as dendritic length and spine density but did not
alter soma size or dendritic complexity. In contrast, testosterone did
not affect any of these parameters in RA, which demonstrates that
exogenous androgens can have selective actions on different song system
neurons. These data are the first evidence for any effect of sex
steroids on synaptic transmission within the song system. Our results
support the idea that endogenous androgens limit sensitive periods for
song learning by functionally altering synaptic transmission in song nuclei.
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