Morphometry of cortical neurons. The best estimation of perikaryon volume from the projection area.

The aim of this investigation is to develop the best approximation procedure for calculating the volumes of the perikarya of oriented cortical neurons. About 1119 nerve cells (area 6 after Brodmann) were identified. The medial cross section (projection area) and the maximal diameter of each cell was measured. The calculation is based on stereometrical models (sphere/cone/ellipsoid). The volume of a sphere of equal projection area has to be corrected for the actual shape of the cell type concerned (conical for pyramidal cells and ellipsoidal for granule and spindle cells). The correction factors are obtained by two different types of graphs. The procedure suggested depends on the available equipment. When working with systems which store only the projection area, the factor obtained for granule cells (0.9) should be used for all cells up to a projection area of 120 microns 2. Larger cells should be corrected by the factor derived for pyramidal cells (0.85). In connection with systems which provide the maximal diameter as well, the correction factors can be worked out by estimating the axial ratio of the neurons. Advanced systems like the Videoplan are able to calculate factors for individual cells.