Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB280

Poster Communications

Peripheral nerve striations represent the sinuous path of axons and are indicative of axonal length

L. Alvey1, J. F. Jones1, M. Pickering1

1. School of Medicine, University College Dublin, Glasthule, Ireland.

The bands of Fontana are striations visible to the naked eye on peripheral nerves, their appearance varying depending on the nerve under observation and its illumination. Their origin and development remains a subject of some debate. A deeper understanding of the development and variability of these bands may help elucidate the mechanisms behind lengthening of axons in peripheral nerves. We provide evidence that the bands are caused exclusively by an axonal wave, and propose a model where band patterning may be used to predict the length of axons within nerves. Adult Wistar rats and C57BL/6 mice were euthanised in accordance with institute guidelines and relevant legislation (directive 2010/63/EU). Sciatic and phrenic nerves were dissected from the animals, fixed and stained with the fluorescent lipophilic dye DiO to highlight the myelinated axons of the nerve using confocal microscopy. The confocal images of nerves were then compared to images of the nerves under oblique illumination that revealed the bands of Fontana. Linear regression analysis showed the number of axonal sine waves in mouse sciatic nerves correlated precisely with the number of bands visible (r2=1; slope=1; n=4), and the bands aligned with the axons, irrespective of the direction of illumination. Band intervals closely correlated with wavelengths in rat and mouse sciatic and phrenic nerves. (1/slope=0.97; r2=0.99; p=0.0001; n=16). The nonlinear course of axons results in axon length which is longer than nerve length, the magnitude of which can be expressed as an axon/nerve length ratio (ANLR). Axon wavelength also correlated with ANLR (1/Slope=-0.002; r2 = 0.48; p=0.0007; n = 20). The ANLR for sciatic nerves (mouse: 1.07±0.01; rat: 1.09±0.02, n=5; Mean±SD) was lower than for phrenic nerves (mouse: 1.18±0.02; rat: 1.16±0.03, n=5; Mean±SD). While the physiological process that regulates ANLR is unknown, our observation that the differences between nerves are greater than the differences between species suggests ANLR is a functional property, rather than simply related to scale. ANLR correlates with axon wavelength, and wavelength correlates with band interval, suggesting that simple inspection of nerve striations may allow calculation of the true axonal lengths in peripheral nerves, relevant for study of peripheral nerve conduction velocity in particular.

Where applicable, experiments conform with Society ethical requirements