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Quarterly Journal of Microscopical Science, Vol s3-100, 499-508, Copyright © 1959 by Company of Biologists

The Use of Teased Preparations and Frozen Sections in Quantitative Studies of Mammalian Peripheral Nerve

C. P. WENDELL-SMITH 1 and P. L. WILLIAMS 1

1 Department of Anatomy, Guy's Hospital Medical School, University of London

When teased preparations of peripheral nerve are examined, the highly refractile myelin sheath acts as a convex lens and affects estimates of axon diameter and sheath thickness. The construction of ray diagrams for different axon-sheath ratios indicates that the degree of magnification varies with this ratio. Models and experiments in which teased fibres were immersed in fluids of different refractive index show that magnification also varies with the relative refractive indices of the sheath and the immersion medium. Fibres from the nervus gastrocnemius medialis (NGM) of the rabbit were teased in Ringer's solution and measurements made with a polarizing microscope. A regression line for 2 x apparent sheath thickness on external diameter was calculated.

Frozen sections (Williams, 1959) of the NGM were prepared, and from these individual fibres were tipped over on to their sides by micromanipulation. A magnification effect similar to that existing in teased fibres was thus introduced and a comparison of their apparent axon diameters was made valid. An analysis of co-variance showed no significant difference in variance, slope, or elevation. It was concluded that these frozen sections provided a satisfactory basis for an estimate of magnification, and that estimates of size relationships made on these frozen sections reflected the natural state as closely as estimates made on isolated teased fibres and corrected for magnification.

A regression line was derived for 2xmyelin sheath thickness on external diameter from intact frozen sections. This line was compared with the regression line for teased fibres and percentage magnification of the axon plotted against external diameter. The graph indicated that this percentage magnification decreased with fibre diameter from over 40% to under 20%.






© The Company of Biologists Ltd 1959