Excitability changes of dorsal root axons following nerve injury: implications for injury-induced changes in axonal Na(+) channels.
Electrophysiological recordings were obtained from rat dorsal roots in a sucrose gap chamber to study changes in Na(+) currents following nerve injury. Application of 4-aminopyridine unmasks a prominent and well-characterized depolarization (delayed depolarization) following the action potential. In our previous studies, this potential, which is only present in cutaneous afferent axons, has been shown to correlate with activation of a slow Na(+) current. The delayed depolarization in the dorsal root was reduced 1 week after sciatic nerve ligation, suggesting a reduction in the kinetically slow Na(+) currents on dorsal root axons [control: 44. 2+/-7.3% (n=5); injury: 7.3+/-4.7% (n=5), P<0.001]. The refractory period of the action potential was reduced following nerve injury, in agreement with biophysical studies indicating faster "repriming" of fast Na(+) currents on cutaneous afferent cell bodies. Dorsal root ligation near the spinal cord also results in a reduction in the delayed depolarization. These results indicate that changes in Na(+) channel organization occur on dorsal root axons following either central or peripheral target disconnection, suggesting trophic support can be derived from either the CNS or the PNS.
Nonaka
T
T
Department of Neurosurgery, Sapporo Medical University School of Medicine, Sapporo, Japan.
Honmou
O
O
Sakai
J
J
Hashi
K
K
Kocsis
J D
JD
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D003714:Denervation / Q000009:adverse effects*; D005727:Ganglia, Spinal / Q000166:cytology / Q000503:physiopathology; D009409:Nerve Crush / Q000009:adverse effects*; D009474:Neurons / Q000378:metabolism; D059348:Peripheral Nerve Injuries; D010525:Peripheral Nerves / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000378:metabolism*; D013126:Spinal Nerve Roots / Q000503:physiopathology*
D015222:Sodium Channels