Principles for the morphological characterization of transmitter-identified nerve cell groups

Principles for a morphometric description of transmitter identified nerve cell groups have been introduced, exemplified on the 5-HT nerve cell group of nucleus raphe dorsalis (B7 cell group), using immunocytochemical procedures to visualize 5-HT. Both cell body parameters (mean diameter, mean perimeter, mean area, shape factor) and cell group parameters (number of cells, mean free distance among cells, volume fraction, gravity centre, major axis slope with respect to the midline) have been considered. These parameters have been obtained by the use of a semiautomatic image analyzer (Kontron MOP AMO2) plugged into an Apple II computer. By the use of this system and of suitable computer programs, it is possible to give a Cartesian representation of 5-HT nerve cell bodies in a coronal section under study. The present work has mainly one aim. To detect whether subgroups exist within a transmitter-identified cell group. Two approaches have been introduced to obtain, on objective grounds, evidence whether or not a group consists of subgroups. The first of these approaches is based on differences in cell body density within the cell group, while the second approach is based on frequency distribution analysis. This second approach is mainly sensitive to shape changes of the cell group.