Journal of Neuroscience, Vol 15, 1879-1890, Copyright © 1995 by Society for Neuroscience
Androgen-induced changes in electrocommunicatory behavior are correlated with changes in substance P-like immunoreactivity in the brain of the electric fish Apteronotus leptorhynchus
JG Dulka, L Maler and W Ellis
Department of Anatomy and Neurobiology, University of Ottawa, Faculty of Medicine, Ontario, Canada.
The hormonal regulation of sex differences in electrocommunicatory behavior
and brain substance P-like immunoreactivity (SPI-ir) were examined in the
weakly electric fish, Apteronotus leptorhynchus. This animal modulates its
electric organ discharge (EOD) to produce discrete electric social signals
(chirps), which function in aggressive and reproductive displays. Males
readily chirp in response to electrosensory stimuli that mimic the presence
of a conspecific; females also chirp in response to such stimuli, but do so
at much lower rates than males. We have recently demonstrated that androgen
treatment enhances chirping behavior in females and may also lead to a
change in chirp quality or structure. In this study, we quantified
androgen- induced changes in chirp structure and simultaneously examined
whether androgens alter the sexually dimorphic pattern of SPI-ir in a brain
region (prepacemaker nucleus, PPn) known to control chirping. Our results
demonstrate that, in females, androgens cause both the induction of
chirping and an alteration of chirp structure; chirps recorded from
androgen-implanted females had longer durations and more dramatic frequency
and amplitude modulations compared to controls, and appear similar to those
reported to be produced during spawning. Moreover, androgen-induced changes
in chirping are correlated with increased expression of SPI-ir within
specific brain nuclei of females. These changes may underly behavioral
changes in chirping, since treated females showed a male-like pattern of
SPI-ir in the PPn. However, alterations in SPI-ir were not restricted to
the PPn, but also occurred in diencephalic regions related to pituitary
function and reproductive behavior. The results suggest that androgens
modulate chirping activity and cause both specific and wide-spread changes
in SPI-ir that may relate to a functional system that interrelates
pituitary function, reproductive behavior, and chirping.
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