The effect of different fixatives on chromatin: cytochemical and ultrastructural approaches

This study explores the effects of two types of fixative on chromatin. The first type (acrolein, glutaraldehyde) engenders a high degree of ultrastructural preservation. The other type are fixatives that are widely used in cytochemistry and cytogenetics (acetic acid, 3:1 by vol. methanol-acetic acid, methanol alone, formaldehyde). Lymphocytes of adult rats so-fixed in vitro were prepared for electron microscopy or microdensitometric evaluations of smears. Assessments were made of variations in their total protein, nuclear basic protein and DNA contents. DNA was determined both as Feulgen-positive material and by its binding of intercalating dyes (Methyl Green, specific for double-stranded polynucleotides). Our results showed that some fixatives break up the chromatin organization by acting on particular components of chromatin fibres. They can thus be considered to be destructive agents in situ. In addition, a revaluation of some aldehyde fixatives is proposed for both ultrastructural and cytochemical research.