Weak action potential backpropagation is associated with high-frequency axonal firing capability in principal neurons of the gerbil medial superior olive
Principal neurons of the medial superior olive (MSO) convey azimuthal sound localization cues through modulation of their rate of action potential firing. Previous intracellular studies in vitro have shown that action potentials appear highly attenuated at the soma of MSO neurons, potentially reflec...
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Veröffentlicht in: | The Journal of physiology 2007-09, Vol.583 (2), p.647-661 |
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Sprache: | eng |
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Zusammenfassung: | Principal neurons of the medial superior olive (MSO) convey azimuthal sound localization cues through modulation of their
rate of action potential firing. Previous intracellular studies in vitro have shown that action potentials appear highly attenuated at the soma of MSO neurons, potentially reflecting specialized
action potential initiation and/or a physically distant site of generation. To examine this more directly, we made dual patch-clamp
recordings from MSO principal neurons in gerbil brainstem slices. Using somatic and dendritic whole-cell recordings, we show
that graded action potentials at the soma are highly sensitive to the rate of rise of excitation and undergo strong attenuation
in their backpropagation into the dendrites (length constant, 76 μm), particularly during strong dendritic excitation. Using
paired somatic whole-cell and axonal loose-patch recordings, we show that action potentials recorded in the axon at distances
> 25 μm are all-or-none, and uniform in amplitude even when action potentials appear graded at the soma. This proximal zone
corresponded to the start of myelination in the axon, as assessed with immunocytochemical staining for myelin basic protein
in single-labelled neurons. Finally, the axon was capable of sustaining remarkably high firing rates, with perfect entrainment
occurring at frequencies of up to 1 kHz. Together, our findings show that action potential signalling in MSO principal neurons
is highly secure, but shows a restricted invasion of the somatodendritic compartment of the cell. This restriction may be
important for minimizing distortions in synaptic integration during the high frequencies of synaptic input encountered in
the MSO. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2007.136366 |