TWO TYPES OF ACTIONS OF NORADRENALINE ON IDENTIFIED AUDITORY EFFERENT
NEURONS IN RAT BRAINSTEM SLICES
Xueyong Wang AND Donald Robertson
The Auditory Laboratory, Department of Physiology, The University of
Western Australia, Nedlands, WA 6907 AUSTRALIA
APStracts 4:0090N, 1997.
ABSTRACT
1. Whole-cell voltage clamp recordings were performed on auditory
olivocochlear neurons in the ventral nucleus of the trapezoid body (VNTB) of
brainstem slices from neonatal rats. Each neuron was identified by retrograde
labeling with Fast Blue injected into the cochlea.
2. Bath application of noradrenaline (NE) 1-10 (M reversibly induced an inward current in 26 out of 38 labeled neurons which were voltage clamped at -75 mV.
This was responsible for the membrane depolarization to NE observed in current clamp mode.
3. The NE induced inward current appeared to be more prominent at -55 mV than
at -75 mV and reversed at around -100 mV. It was attenuated but not prevented
by 20 mM TEA, and persisted when the perfusate contained 2 mM Cs+ or 100 (M
Cd2+. However, the NE-induced inward current was attenuated to varying degrees in a 0-Ca2+ solution.
4. I-V plots revealed that NE caused a decrease in membrane K+ conductance. A
suppression of voltage-gated Ca2+ currents by NE was also observed. The
excitatory action of NE was blocked by the (-adrenoreceptor antagonist
phentolamine. The (1-adrenoreceptor agonist phenylephrine had a similar effect to NE.
5. In 6 out of 38 labeled neurons, an inhibitory action of NE (1-10 (M) was
observed that appeared to be due to an activation of an inwardly rectified K+
current, which caused hyperpolarization of resting membrane potentials in
current clamp mode. This inhibitory response was independent of external Ca2+
and abolished by 2-5 mM Cs+ or 0.5 mM Ba2+ applied in the perfusate.
6. The receptors involved in the inhibitory actions of NE are not clear. The
effect was partially and reversibly blocked by propranolol (10 (M), a (-
adrenoreceptor antagonist. However, isoprenaline (10 (M), a (-adrenoreceptor
agonist, failed to induce any effect. On the other hand, the inhibitory effect was irreversibly blocked by pretreating with phentolamine (5-10 (M).
Phenylephrine (5-10 (M) had no effect.
Received 8 April 1997; accepted in final form 12 June 1997.
APS Manuscript Number J280-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997