Abstract
Purpose :
Retinal ganglion cells generate a pattern of action potentials to communicate visual information. Myelin, an insulating sheath, facilitates signal propagation by wrapping around axons and, when deficient (as observed in patients with optic neuritis), can cause significant visual deficits. However, the relationship between optic nerve function and the extent of myelination is currently unknown.
Methods :
We tested if myelination patterns are correlated with changes in optic nerve function during postnatal development using extracellular nerve recordings, immunohistochemistry, western blot, and scanning electron microscopy.
Results :
Comparing compound action potentials from C57Bl6 mice across ages 4-12 wks revealed an increase in the number of functional axons and shifts toward more fast-conducting axon populations at 5 and 8 wks (p<0.05, n=8). At these ages, nerve assessments suggest increases in myelin and neurofilament protein concentrations (n=2) and lower g-ratios (n>2). Increased expression of a mature sodium ion channel (Nav 1.6) at nodes of Ranvier was observed at 6 wks (p<0.05, n=3), while axon diameter, axon density, and nodal density remained unchanged across ages.
Conclusions :
Changes in the normal optic nerve to favor faster axonal conduction correlate with additional myelin proteins, thicker myelin around axons, and node maturity, suggesting that these properties are critical in the refinement of optic nerve signaling during postnatal maturation.
This is a 2021 ARVO Annual Meeting abstract.