[Histochemical demonstration of sialic acid-containing compounds in the CNS of mice and goldfish by means of the mPAT ("mild" periodic acid-thionine)-method (author's transl)]

High and low molecular weight tracers for the electron microscopical detection of sialoglycoconjugates

Hydrazide-derivative tracers of different molecular weights have been synthesized for use in the electron microscopical detection of sodium periodate-oxidized sialyl residues of glycoconjugates in various tissues and cells. Haemundecapeptide hydrazide, horseradish peroxidase hydrazide, and Limulus polyphemus haemocyanin hydrazide were obtained by coupling adipic acid dihydrazide to the tracers with the aid of water-soluble carbodiimide. The enzymatic tracers thus prepared retained their peroxidatic activity. On conversion to the hydrazide derivative, the haemocyanin molecule dissociated into its hexameric subunits. In order to test by transmission electron microscopy the ability of the conjugates to bind to the sialoglycoconjugates of endothelial cell surfaces, each tracer was perfused in situ into rat pancreatic vasculature previously oxidized with 1 mM sodium periodate. The three tracers characteristically labelled the various microdomains of the luminal cell coat of the capillary endothelial cell. The electron opacity of the haemocyanin subunits allowed their easy detection when bound to the cell surface or to components of the extracellular matrix. The bound markers were not displaced by a high ionic strength buffer, and did not label desialylated cell surfaces. These results indicate that the three hydrazide-derivative tracers may be useful tools for the electron microscopical detection of cellular and extracellular sialoglycoconjugates.

Histochemical localization of neuraminidase in the CNS of mice and fish by means of 5-brom-3-indolyl-alpha-ketoside of 5-N-acetyl-D-neuraminic acid (BI-NeuAc)

The applicability of the 5-brom-3-indolyl-alpha-ketoside of N-acetyl-D-neuraminic acid (BI-NeuAc) as substrate for the histochemical indication of neuraminidase (GOSSRAU et al. 1977) was examined in frozen sections of brain, small intestine and kidney from suckling and adult mice and respectively from a cichlid fish (Sarotherodon mosambicus) with and without formaldehyde fixation. Following biochemical investigations using tritiated gangliosides as substrate a decrease in the activity of neuraminidase took place from about 50 to 80% after tissue fixation with formaldehyde. Nevertheless significant histochemical reactions were found only in fixed tissue sections. The specificity of this reaction was shown by means of inhibitions tests using 2,3-dehydro-2-desoxy-N-acetyl-neuraminic acid according to KUMAR et al. (1981). In contrast to distinct staining of neuraminidase activity in the small intestine and kidney, only faint reactions occurred in brain sections. From this it is concluded that the application of the new synthetic substrate for quantitative staining of neuraminidase seems to be not very suitable for the CNS.