Simplified nerve cell counting in the rat brainstem with the physical disector using a drawing-microscope

A simple modification of the physical disector is presented which is used to count the number of neurons in the hypoglossal nucleus of the rat in a series of paraffin sections. One disector consists of two adjacent sections (6 microm thick) that have been Nissl-stained with cresyl fast violet. In the first step of the procedure each of the two sections in investigated separately with a drawing-microscope. The boundary of the hypoglossal nucleus and the position of neurons devoid of, or containing a part of, the cell nucleus in the plane of the section are marked on transparent paper. In the second step, these two drawings are placed one upon another, aligned and the number of cell profiles that show a cell nucleus in one but not in both drawings counted. This modification of the disector method for cell counting needs no specialized equipment, simply a light microscope with drawing apparatus, and can be combined with histochemical studies of other sections from the same tissue block.