THE ACTION OF LOCAL-ANESTHETICS ON MYELIN STRUCTURE AND NERVE-CONDUCTION IN TOAD SCIATIC-NERVE

X-ray scattering and electrophysiological experiments were performed o n toad sciatic nerves in the presence of local anesthetics. In vitro e xperiments were performed on dissected nerves superfused with Ringer's solutions containing procaine, lidocaine, tetracaine, or dibucaine. I n vivo experiments were performed on nerves dissected from animals ane sthesized by targeted injections of tetracaine-containing solutions. I n all cases the anesthetics were found to have the same effects on the x-ray scattering spectra: the intensity ratio of the even-order to th e odd-order reflections increases and the lattice parameter increases. These changes are reversible upon removal of the anesthetic. The magn itude of the structural changes varies with the duration of the superf usion and with the nature and concentration of the anesthetic molecule . A striking quantitative correlation was observed between the structu ral effects and the potency of the anesthetic, Electron density profil es, which hardly showed any structural alteration of the unit membrane , clearly indicated that the anesthetics have the effect of moving the pairs of membranes apart by increasing the thickness of the cytoplasm ic space. Electrophysiological measurements performed on the very samp les used in the x-ray scattering experiments showed that the amplitude of the compound action potential is affected earlier than the structu re of myelin (as revealed by the x-ray scattering experiments), wherea s conduction velocity closely follows the structural alterations.