Staining of biological material for the scanning electron microscope

Ventricular trabeculations in the chick embryo heart and their contribution to ventricular and muscular septal development

Sixty-two chick embryo hearts were studied at incremental stages of development (Hamburger-Hamilton stages 16 to 39) by scanning electron microscopy following 3% glutaraldehyde fixation and critical point drying. Early in cardiac development, the primitive ventricle becomes homogeneously trabeculated with highly organized sheets of myocytes lined by endocardial cells, with the trabeculae generally oriented in the dorsoventral direction. Coalescence of these trabecular sheets begins at stage 26, initially at the area of the bulboventricular flange, and later proceeding caudally toward the floor of the ventricle. The fusion process is finished by stage 30, resulting in a muscular ventricular septum that has now divided the primitive ventricle into right and left ventricles. Further growth of the ventricular septum is by continued fusion of the adjoining trabecular sheets. Remnants of the apposing trabecular sheets are found in the solidified muscular septum in the form of endocardial channels. We suggest that persistent patency of these channels results in muscular ventricular septal defects.

Observation of cytochemical alkaline phosphatase activity on the plasma membrane of cultured rat hepatocytes by backscattered electron imaging

Distribution of alkaline phosphatase (ALPase) activity on the plasma membrane of rat hepatocytes in primary monolayer culture was observed using the backscattered electron image (BEI) mode. Apparent reaction product was seen in hepatocytes cultured for 48 or 72 hours in a concentration of 8 X 10(5) cells per ml, and those cultured for 72 or 96 hours in a concentration of 6 or 4 X 10(5) cells per ml. The reaction product was observed as scattered fine dots, as spots, and as bands along the cell edge, with high contrast in flattened polyhedral hepatocytes forming cell trabeculae. The deposition of the reaction product was generally more abundant at the periphery of the cell trabeculae. X-ray microanalysis revealed that the reaction product contains both lead and phosphorus as real ALPase reaction product. In transmission electron microscopy, the reaction product was exclusively localized on the external surface of the plasma membrane. However, the plasma membrane adjoining the culture substratum was devoid of the reaction product. Further, the highest biochemical ALPase activity appeared in earlier culture stages when the density of cultured cells was larger. Thus, during a few days of culture, ALPase activity increases on the plasma membrane predominantly at the periphery of the hepatocyte trabeculae. This increase in the activity might be related to the mechanism of preserving the cell shape.

The localization of histochemical and autoradiographic products in the scanning electron microscope by means of atomic number contrast

The role of atomic number contrast and backscattered imaging in the localization of histochemical products and reagents is reviewed. Particular attention is given to the localization of enzymatically released products. A backscattered imaging method is presented which permits the simultaneous demonstration of two label elements in a cryosection examined in the scanning electron microscope. An azo-dye method for the localization of acid phosphatase is combined with an autoradiographic technique for demonstrating [3H]thymidine incorporation. Atomic number contrast, produced by backscattered electrons, permits the detection of a bromine-labelled azo dye, denoting sites of acid phosphatase activity within a cryosection and the simultaneous display of the sites of the silver deposited in an overlying photographic emulsion. The former reveals acid phosphatase to be predominantly associated with thymocyte death and macrophage activity in mouse thymus. The latter pin-points the thymocytes as the main sites of [3H]thymidine incorporation. Atomic number contrast has a useful potential for differentiating between spatially separated histochemical products of differing atomic number in a structural context and also allows a flexible degree of subsurface localization.

Immunocytochemical localization of intracellular antigens with SEM

A method for the localization of intracellular antigens with a scanning electron microscope using peroxidase-labelling antibodies is described. A search for a hydrogen donor which may be deposited at the sites of antigen by enzymatic action and emit secondary electrons or generate backscatter electrons was made. It was found that when 4-chloro-1-naphthol was used, the peroxidase deposited reaction product which resulted in a strong secondary electron emission at the site of antigen. With this method, the presence of luteinizing hormone in secretion granules and other cytoplasmic structures of gonadotropic cells was demonstrated. The level of detection of intracellular antigens with this method is not as high as that detectable with light microscopical examination of the same specimens, that is, more reaction product at the site of antigen is required to be detectable with scanning electron microscopy than with light microscopy. In spite of the lack of high sensitivity, the intracellular antigens may be localized with the method described.