TY - JOUR
T1 - Persistent abnormalities of membrane excitability in regenerated mature motor axons in cat
AU - Moldovan, Mihai
AU - Krarup, Christian
N1 - Keywords: Action Potentials; Animals; Axons; Cats; Motor Neurons; Nerve Regeneration; Tibial Nerve
PY - 2004
Y1 - 2004
N2 - The purpose of our study was to assess by threshold tracking internodal and nodal membrane excitability during the maturation process after tibial nerve crush in cat. Various excitability indices (EI) were computed non-invasively by comparing the threshold of a submaximal compound motor potential at different stimulation durations (strength-duration relationship), after a conditioning nerve impulse (recovery of excitability), or during the application of a polarizing current (threshold electrotonus). Four months after the lesion, regenerated nerves showed a higher rheobase, shorter chronaxie, shorter refractory period and higher than normal threshold variations during threshold electrotonus (TE). A partial recovery was observed during the first 2 years of maturation. The recovery to depolarizing TE seemed complete but all other EI remained abnormal even after 5 years of regeneration, the most pronounced being the 157 +/- 8% (mean +/- S.E.M.) increase in threshold during hyperpolarizing TE compared with 94 +/- 4% in controls. These EI abnormalities are consistent with increased input impedance. Nevertheless, the time course of maturation and incomplete recovery of EI could only be partially explained by changes in fibre morphology. The highly abnormal response to hyperpolarizing but not to depolarizing TE suggests that voltage-dependent membrane function also remained abnormal, possibly due to membrane hyperpolarization.
AB - The purpose of our study was to assess by threshold tracking internodal and nodal membrane excitability during the maturation process after tibial nerve crush in cat. Various excitability indices (EI) were computed non-invasively by comparing the threshold of a submaximal compound motor potential at different stimulation durations (strength-duration relationship), after a conditioning nerve impulse (recovery of excitability), or during the application of a polarizing current (threshold electrotonus). Four months after the lesion, regenerated nerves showed a higher rheobase, shorter chronaxie, shorter refractory period and higher than normal threshold variations during threshold electrotonus (TE). A partial recovery was observed during the first 2 years of maturation. The recovery to depolarizing TE seemed complete but all other EI remained abnormal even after 5 years of regeneration, the most pronounced being the 157 +/- 8% (mean +/- S.E.M.) increase in threshold during hyperpolarizing TE compared with 94 +/- 4% in controls. These EI abnormalities are consistent with increased input impedance. Nevertheless, the time course of maturation and incomplete recovery of EI could only be partially explained by changes in fibre morphology. The highly abnormal response to hyperpolarizing but not to depolarizing TE suggests that voltage-dependent membrane function also remained abnormal, possibly due to membrane hyperpolarization.
U2 - 10.1113/jphysiol.2004.069476
DO - 10.1113/jphysiol.2004.069476
M3 - Journal article
C2 - 15297575
SN - 0022-3751
VL - 560
SP - 795
EP - 806
JO - The Journal of Physiology
JF - The Journal of Physiology
IS - Pt 3
ER -