Application of automatic image analysis for morphometric studies of peroxisomes stained cytochemically for catalase. I. Electron-microscopic application.

The feasibility of the application of an electronic image analyzer, the Texture Analysis System (TAS) (Leitz Wetzlar, FRG), for fast automatic ultrastructural morphometric studies of hepatic peroxisomes has been investigated. Rat liver peroxisomes were stained selectively with the alkaline DAB procedure for localization of catalase in order to obtain sufficient contrast for automatic detection by TAS. Electron micrographs of ultrathin sections from this material were analyzed both automatically by TAS and manually by using a digitizer tablet connected with an Apple IIe microcomputer. The results showed negligible differences. As far as the speed of the operation is concerned, the image analysis was 4-5 times faster than the manual technique. In further studies, the importance of using DAB-stained sections for accurate morphometric studies of peroxisomes was demonstrated by comparing the results of such DAB-stained preparations with unstained material. This revealed that the numerical density was lower and the average profile diameter higher in unstained sections. The value for volume density was also affected, being about 30% lower in such preparations. It is likely that in unstained preparations small peroxisomes without crystalline nucleoids were frequently not identified as such and were not taken into account in morphometric calculations. These observations establish that computer-controlled electronic image analysis in conjunction with selective cytochemical staining of peroxisomes for catalase provides a fast, accurate and reliable method for ultrastructural morphometric studies of this organelle in rat liver.