Study of myelin structure changes during the nerve fibers demyelination

Abstract

Raman, NMR and EPR spectroscopy and electrophysiology methods were used to investigate the excitability and the packaging of myelin lipid layers and its viscosity during nerve exposure to pronase E. It was established that during exposure of nerve to pronase E the action potential (AP) conduction velocity and the Schwann cell (SC) (or myelin) water ordering increases, but the nerve myelin refractive index and internode incisions numbers decrease. This effect included two periods-short- and long-time period, probably, because the first one depends on SC protein changes and the second one-on the nerve fiber internode demyelination. It was concluded that high electrical resistance of myelin, which is important for a series of AP conduction velocity, not only depends on nerve fiber diameter and the myelin lipid composition, but also on the regularity of myelin lipid fatty acids and myelin lipid layer packing during the axoglial interaction.

Fig 1

The amplitude (A) and the velocity of AP propagation (B) changes during nerve exposure to pronase E (0,2%). Significant difference (p <0.05).

Fig 2. The phase image parameters of myelin nerve fiber (1–12).

(1–2)—the paranodal areas with Ranvier’s node length; (3–4)—Ranvier’s node diameter; (5–6)–diameter of nerve fiber internodal region (in incisures area); (7–8)—diameter of axon in incisures area; (9–10)—diameter of nerve fiber in internodal region; (1–12)—diameter of axon in internodal region; I—the OPD in Ranvier’s node; II—the OPD in the nerve fiber center; III- OPD in the nerve fiber boundary.

Fig 3. The dynamics of OPD profile changes along the scan-line (μM) through NR.

(A); in internode region of the myelin fiber (B); the perpendicular to the normal nerve fiber and along the nerve fiber (C), during exposure of the nerve to pronase E.

Fig 4

The temperature dependence of nerve fibers: on water T₂ (1) and on the intensity ratio I₁₅₂₄/I₁₁₅₁ of carotenoids Raman spectra (2) changes. (Insert) The spin-spin relaxation time of protons (T₂) during 40 min nerve exposure to pronase E. (control (nerve exposure to D₂O)—white column; nerve exposure—shaded column). The mean value of T₂ in the control corresponding to 849 ms is taken as 100%. Significant difference (p <0.05).

Fig 5. Raman spectra of myelin sheath of sciatic nerve fiber.

Raman scattering was excited by 532-nm (A) and 780 nm (B) laser with 0.8 mW power, integration time was 50 s.

Fig 6

Changes in the ratio of I₁₅₂₄/I₁₁₅₁ RS bands of carotenoids during nerve exposure to pronase E (A), and the rotational correlation times (τ) of DS-16 changes during nerve exposure to pronase E and methyl-β-cyclodextrin (10⁻² M) (B). Significant difference (p <0.05).

Fig 7. The dynamics of the nerve fatty acids RS peak ratio changes during nerve exposure to pronase E.

Raman scattering was excited by 780 nm laser with power of 0.8 mW, registration time was 50 s. Significant difference (p <0.05).