| Popis: |
Neurofilaments (NFs) constitute the most abundant cytoskeletal structure in large myelinated axons. NFs are made by the co-polymerization of three intermediate filament proteins, NF-L, NF-M, and NF-H that are expressed exclusively and in the most neurons. The ! aim of this study was to examine electrophysiological properties of myelinated axons with altered morphology expressing different intermediate filament proteins (NF-L, NF-M and NF-H knockout mice) that resulted in myelinated fibres with smaller axon diameter and altered cytoskeletal structure. Steady state membrane properties, action potentials (AP) and single axon refractory period were measured on isolated sciatic nerves in vitro using intracellular current-clamp technique or extracellular sucrose gap recording. Transgenic animals showed several deficits in physiological properties of low threshold myelinated fibres: conduction velocity (CV) was significantly decrease in NF-L and NF-M knockout animal (12.54ą3.49 m/s and 23.54ą6.6 m/s, respectively vs. 42.80ą10 m/s in controls; n=25; 22o C); recovery period of AP was increased transgenic animals. Compound action potential (CAP) area in NF-L/-was significantly (305%2! 9 decrease. In conclusion, reduction in CV is explainable by morphological changes (smaller axon diameter, relatively thicker myelin); changes in refractory period and CAP area indicate a possible dysfunction of Na+ channels. These results suggest a pissible involvement of NFs in regulation or expression of ion channels in peripheral myelinated axons. |
