Light microscopic catalase histochemistry in mussel digestive gland tissue

Different light microscopical procedures for the histochemical demonstration of catalase were tested in cryostat sections of mussel digestive gland tissue by using both benzidine and diaminobenzidine (DAB) as hydrogen donors. The selected procedure, which was also applied to mouse liver for comparative purposes, consisted of incubation in media containing 0.2% DAB and 0.3% H2O2 at pH 10.4 for 35 min at 42 degrees C. Addition of 0.01 M imidazole to the incubation medium increased the staining intensity of the histochemical procedure. The positive reaction product was localized in epithelial cells lining the digestive tubules and the ducts. The histochemical reaction was inhibited partially by aminotriazole or sodium azide and disappeared completely by omission of H2O2 from the incubation medium. On the other hand, heat resistant non-enzymatic reactions were observed in sites known to contain lipofuscins such as epithelial cells of the gastrointestinal tract and connective tissue brown cells.