Holger Jastrow, Marc-A. von Mach and Lutz Vollrath

Anatomisches Institut, Johannes Gutenberg-Universität Mainz, Becherweg 13, D-55099 Mainz

The disector is the only objective method for quantification of particles of variable size in a given volume. Here cell organelles are identified on adjacent sections, but only those present in one section are counted. When counting very rare structures in transmission electron-microscopic sections (physical disector) the usual procedure of counting on photographs is limited by economical reasons (e.g. photographs highly outnumbering investigated structures). Hence to apply this unbiased stereological method a modification of the physical disector has been developed: (i) The necessity of screening corresponding areas was ensured by examining tissue areas along the edges of ultrathin sections. (ii) The size of the reference area was determined by measuring the lengths of the section's edges by means of a Morphomat multiplied by the width of the investigated tissue zone, corresponding to the diameter of the electron microscope screen. (iii) Disector counting was carried out simultaneously on both sections (bidirectional disector) to increase volume of reference. In the present study pineal synaptic organelles (SO's) were quantified by disector while their profile number was determined by the previously applied counting method referring to areas (standard 20,000 µm²). While investigation of animals killed at noon or midnight revealed identical profile numbers per area, the disector method revealed ~ 20% higher day values. This was explained by changes in dimensions of SO's. Thus specific proportion factors need to be determined allowing to estimate number of structures per volume based on counts in the standard area.