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First published online on August 17, 2006.
Copyright © 2006 by The Physiological Society
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jphysiol.2006.114702v1
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Received June 5, 2006
Revised July 11, 2006
Accepted after revision August 15, 2006

Hyperpolarization-activated currents are differentially expressed in brainstem auditory nuclei

Katarina E Leao1*, Richardson N Leao1, Hong Sun2, Robert E.W. Fyffe2, and Bruce Walmsley1

1 The John Curtin School of Medical Research
2 Wright State University

* To whom correspondence should be addressed. E-mail: katarina.leao{at}anu.edu.au.

The hyperpolarization-activated cation current (Ih) may influence precise auditory processing by modulating resting membrane potential and cell excitability. We used electrophysiology and immunohistochemistry to investigate the properties of Ih in three auditory brainstem nuclei in mice; the anteroventral cochlear nucleus (AVCN), the medial nucleus of the trapezoid body (MNTB) and the lateral superior olive (LSO). Ih amplitude varied considerably between these cell types, with the order of magnitude LSO>AVCN>MNTB. Kinetically, Ih is faster in LSO neurons, and more active at rest, compared to AVCN and MNTB cells. The half-activation voltage is -10 mV more hyperpolarized for AVCN and MNTB cells compared to LSO neurons. HCN1 immunoreactivity strongly labelled AVCN and LSO neurons, while HCN2 staining was more diffuse in all nuclei. The HCN4 subunit displayed robust membrane staining in AVCN and MNTB cells but weak labelling of the LSO. We used a dynamic clamp, after blocking Ih, to reinsert Ih to the different cell types. Our results indicate that the native Ih for each cell type influences the resting membrane potential and can delay the generation of action potentials in response to injected current. Native Ih increases rebound depolarisations following hyperpolarizations in all cell types, and increases the likelihood of rebound action potentials (particularly in multiple-firing LSO neurons). This systematic comparison shows that Ih characteristics vary considerably between different brainstem nuclei, and that these differences significantly affect the response properties of cells within these nuclei.


Key words: Auditory system • Hyperpolarization-activated channels • Membrane current




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