Howells, J;
Bostock, H;
Burke, D;
(2016)
Accommodation to hyperpolarization of human axons assessed in the frequency domain.
Journal of Neurophysiology
, 116
(2)
pp. 322-335.
10.1152/jn.00019.2016.
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Abstract
Human axonsin vivowere subjected to subthreshold currents with a threshold-"ZAP" profile (Impedance [ Z: ] A: mplitude P: rofile) to allow the use of frequency domain techniques to determine the propensity for resonant behavior, and to clarify the relative contributions of different ion channels to their low-frequency responsiveness. Twenty-four studies were performed on the motor and sensory axons in 6 subjects. The response to oscillatory currents was tested between 'DC' and 16 Hz. A resonant peak at ~2 to 2.5 Hz was found in the response of hyperpolarized axons, but there was only a small broad response in axons at resting membrane potential (RMP). A mathematical model of axonal excitability developed using DC pulses provided a good fit to the frequency response for human axons, and indicated that the hyperpolarization-activated currentIh, and the slow potassium currentIKsare principally responsible for the resonance. However the results indicate that if axons are hyperpolarized more than -60% of resting threshold, the only conductances that are appreciably active areIhand the leak conductance - i.e., that the activity of these conductances can be studiedin vivovirtually in isolation at hyperpolarized membrane potentials. Given that the leak conductance dampens resonance it is suggested that the -60% hyperpolarization used here is optimal forIh As expected differences between the frequency responses of motor and sensory axons were present and best explained by reduced GKs, up-modulation ofIhand increased persistent Na(+)current,INaP(due to depolarization of RMP) in sensory axons.
| Type: | Article |
|---|---|
| Title: | Accommodation to hyperpolarization of human axons assessed in the frequency domain |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1152/jn.00019.2016 |
| Publisher version: | http://dx.doi.org/10.1152/jn.00019.2016 |
| Language: | English |
| Additional information: | Copyright © 2016 by the American Physiological Society |
| Keywords: | Axonal excitability, frequency domain, motor axons, resonance, sensory axons |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/1482281 |
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