Differences in excitability between median and superficial radial sensory axons.
OBJECTIVE
The aim of this study was to investigate differences in excitability properties of human median and superficial radial sensory axons (e.g., axons innervating the glabrous and hairy skin in the hand). Previous studies have shown that excitability properties differ between motor and sensory axons, and even among sensory axons between median and sural sensory axons.


METHODS
In 21 healthy subjects, threshold tracking was used to examine excitability indices such as strength-duration time constant, threshold electrotonus, supernormality, and threshold change at the 0.2 ms inter-stimulus interval in latent addition. In addition, threshold changes induced by ischemia for 10 min were compared between median and superficial radial sensory axons.


RESULTS
Compared with radial sensory axons, median axons showed shorter strength-duration time constant, greater threshold changes in threshold electrotonus (fanning-out), greater supernormality, and smaller threshold changes in latent addition. Threshold changes in both during and after ischemia were greater for median axons.


CONCLUSIONS
These findings suggest that membrane potential in human median sensory axons is more negative than in superficial radial axons, possibly due to greater activity of electrogenic Na(+)/K(+) pump. These results may reflect adaptation to impulses load carried by median axons that would be far greater with a higher frequency.


CONCLUSIONS
Biophysical properties are not identical in different human sensory axons, and therefore their responses to disease may differ.
Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
Yumi
Y
Fujimaki
Kazuaki
K
Kanai
Sonoko
S
Misawa
Kazumoto
K
Shibuya
Sagiri
S
Isose
Saiko
S
Nasu
Yukari
Y
Sekiguchi
Shigeki
S
Ohmori
Yu-ichi
Y
Noto
Yumiko
Y
Kugio
Toshio
T
Shimizu
Shiro
S
Matsubara
Cindy S Y
CS
Lin
Satoshi
S
Kuwabara
D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000368:Aged; D001369:Axons / Q000502:physiology*; D055592:Biophysical Phenomena / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007511:Ischemia / Q000503:physiopathology; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008875:Middle Aged; D011826:Radial Nerve / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000502:physiology*; D012867:Skin / Q000294:innervation*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology
D000254:Sodium-Potassium-Exchanging ATPase