A new method for expressing axonal size: rat optic nerve analysis.

Analysis of the shape of the cross sections of adult rat optic nerve axons reveals that the majority of axons do not have a true circular shape. Therefore, determination of axonal size has to utilize methods of approximation. The method presented here utilizes three calculated parameters for expression of axonal size: (i) axonal diameter, as calculated from its area, or (ii) axonal diameter, as calculated from its perimeter, both assuming axonal shape to be a perfect circle and (iii) axonal shape factor, which represents the divergence of the axon from a perfect circular shape. The use of the calculated axonal diameter, with a correction for its shape factor, provides a normalized way of expressing axonal size.