A stereological method for estimating the total length and size of myelin fibers in human brain white matter.

A practically unbiased stereological method to obtain estimates of the volume and total length of nerve fibers in brain white matter is described. The sampling scheme is designed so that the majority of brain white matter is left intact, thus providing the possibility for resampling and further analysis. Uniform sampling of one complete hemispherical white matter is performed. The volume fraction of nerve fibers in white matter is estimated by point counting. The total length of nerve fibers was estimated from the product of the volume of white matter, obtained with the Cavalieri principle, and the fiber length density, obtained from the isotropic, uniform random sections which were ensured by the isector. The size of nerve fibers was derived by measuring the profile diameter perpendicular to its longest axis. The influence of the postmortem fixation delay on nerve fiber parameters was investigated in one dog and one pig. The criteria for identification of nerve fiber profiles at light microscopy were evaluated using electron microscopy.