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 Previous Article
Journal of Neuroscience, Vol 16, 2860-2868, Copyright © 1996 by Society for Neuroscience
Opposing actions of androgen and estrogen on in vitro firing frequency of neuronal oscillators in the electromotor system
Je Schaefer and HH Zakon
Department of Zoology and Center for Developmental Biology, The University of Texas at Austin, 78712, USA.
The South American knifefish (Apteronotus leptorhynchus), or brown ghost,
produces a high-frequency (600-1000 Hz) sinusoidal electric organ discharge
(EOD) with males discharging at higher frequencies than females. In
addition, each fish has a unique EOD frequency within the frequency range
of its gender. The electromotor circuit responsible for EOD production
consists of a medullary pacemaker nucleus (PMN) and spinal electromotor
neurons (EMNs). In vitro spinal slice recording showed that, similar to the
PMN, EMNs fire spontaneously at rates near the EOD frequency of each fish.
The persistence of firing 2 weeks after high spinal transaction
demonstrated that spontaneous firing rate was intrinsic to the EMNs and was
not dependent on presynaptic input. We confirmed that 11-ketotestosterone
(11 kT) raised and 17-beta-estradiol (E2) lowered the EOD frequency of
intact fish. Because electromotor cells fire spontaneously near EOD,
frequency, we investigated whether these steroids affect endogenous firing
rates. Steroid implants were made in normal or spinally transected fish.
Two weeks later, PMNs of normal fish and EMNs of transected fish were
recorded in vitro. 11 kT increased and E2 decreased the intrinsic firing
rate of neurons in the PMN and the EMNS. Hormones shifted the intrinsic
firing rates of EMNS, although they were synaptically isolated during the
hormone exposure.
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