Communicating junctions of the human sensory retina. A freeze-fracture study

Using the freeze-fracture technique communicating junctions could be identified between the cells of the adult human sensory retina. Communicating junctions with particles arranged in linear or circular rows as well as in small aggregates were found between adjacent photoreceptor endings. Communicating junctions with particles forming plaques were localized in the inner plexiform layer. They were isolated between unidentified cell processes or lay close to active sites of chemical synapses, thus suggesting the occurrence of "mixed" (chemical and electrical) synapses in this layer. Furthermore, communicating junctions were detected between portions of Müller's cells.

[Study on the effect of formaldehyde on the immunological reactivity and morphology of hepatitis B-antigen (author's transl)]

Treatment of purified HB-antigen with formaldehyde solution changes its immunological reactivity and its morphology. A decrease in antigen activity by formaldehyde treatment could be demonstrated by radial immunodiffusion and by radioimmunoassay (Fig. 1). Electron microscopic studies revealed a segmentation of tubular HBAg particles into small round forms (Fig. 3) and a shift of the ratio tubular forms: spherical forms in favour of the spherical particles (Table 1). These findings support the hypothesis that 20 nm particles originate from a division of tubular forms. Round forms became smaller after formaldehyde treatment (Fig. 4). The treatment with formaldehyde changed neither the density of HBsAg testes in CsCl gradients, nor the immunologic identity tested in immunodiffusion tests (Fig. 2). All prescribed effects were observed only in the high concentrations of formalin (10 and 1%), whereas in the concentration of 0.1%, which is usually used for inactivations in the development of vaccines, no immunological and morphological changes of the HBAg could be seen.

Electron-microscopic histochemistry of the most peripheral retinal vessels

The reaction of Thiéry (periodic acid-thiocarbohydrazide-silver proteinate) has been applied for histochemical analysis of the structures composing the halo of the most peripheral human retinal vessels. It is suggested that glycoproteins lie in the ground substance of the halo as well as well as in the basement membranes of endothelial cells, pericytes, and Müller cells. Glycogen particles were found in endothelial cells, in pericytes and especially in Müller cells.

Lysosomes in normal and degenerating neuroblasts of the chick embryo spinal ganglia. A cytochemical and quantitative study by electron microscopy

Lysosomes were studied by both cytochemical and quantitative methods in normal and degenerating neuroblasts of the chick embryo spinal ganglia. In normal neuroblasts (primitive and intermediate neuroblasts) both primary lysosomes and autophagic vacuoles were found; these organelles were usually located in the region containing the Golgi complex. In degenerating neuroblasts lysosomes appeared sharply decreased in number with respect to normal neuroblasts. Moreover, lysosomes were always evident as intact organelles surrounded by a membrane and the acid phosphatase activity appeared localized exclusively within these bodies. A diffuse distribution of acid phosphatase activity was only found in a limited number of cases during the terminal stage of the process. Possibly in these cases the enzymatic activity depended on the cells which enveloped the degenerated neuroblast remnants. The present results indicate that lysosomes do not play a primary role in the degenerative process studied.

Freeze-fracture aspects of the perineurium of spinal ganglia

The internal portion of the capsule of the spinal ganglia of rabbit is composed of continuous superimposed layers of flattended cells (perineurium). In replicas, extensive meshworks of strands, presumably forming zonulae occludentes, are found between the perineurial cells of the same layer. Adjacent layers are joint by maculae occludentes located on the lateral processes of the perineurial cells. Occasionally small gap junctions lie within the meshes of the zonulae occludentes.

Intercellular junctions in the organ of Corti as revealed by freeze fracturing

The junctions between the cells of the organ of Corti have been investigated with the freeze-fracture method in the chinchilla inner ear. Numerous gap junctions have been found among all the supporting cells, particularly at the level of their basal part. This means that the supporting cells have their cytoplasm electrotonically and metabolically coupled. Gap junctions were not observed between supporting and sensory cells nor between sensory cells and nerve endings. At this level the transmission should be chemically mediated.

[Connection complex on the cells of Reissner's membrane in freeze-fractured preparations]

The Reissner membrane of the chinchilla inner ear was studied with the freeze-fracture method. Zonulae occludentes, composed of 2 to 8 strands, seal the intercellular space close to the endolymphatic surface. They are morphologically simialr to those seen between the marginal cells of the stri vascularis, but much less developed than those between the basal strial cells.

Freeze-fracture faces of the perineurial sheath of the rabbit sciatic nerve

Replicas of the perineurium of rabbit sciatic nerve fascicles show extensive zonulae occludentes between the flattened cells of each perineuriallamella. The junctions formed by the zonulae occludentes are of the morphologically 'tight' type. Therefore, theyare likely to represent the anatomical site of the diffusion barrier previously demonstrated by other morphological and physiological methods. Neighbouring perineurial lamellae are connected to one another by numerous maculae occludentes, some of which lie on thelateral processes of the perineurial cells. Within the meshes of the maculae occludentes and close tothem, small gap junctions can be observed.

Zonulae occludentes of the myelin lamellae in the nerve fibre layer of the retina and in the optic nerve of the rabbit: a demonstration by the freeze-fracture method

Ridges and grooves composing extensive zonulae occludentes are revealed by the freeze-fracture method on split myelin lamellae in the nerve fibre layer of the retina and in the optic nerve of the rabbit. The junctions are located immediately internal to the outer loop of the myelin sheath and in corresponding areas of deeper myelin layers. They follow a straight or gently undulating course along the axis of the fibres. Only at the paranodal region of nodes of Ranvier do they deviate and assume a transverse course, The strands of these zonulae occludentes probably represent the radial thickenings of the intraperiod line described in thin sections.

The fine structural localization of acetylcholinesterase activity in the retina and optic nerve of rabbits

In the rabbit retina acetylcholinesterase activity is localized in the perinuclear cisterna, in the cisternae of the rough surfaced endoplasmic reticulum and in the Golgi apparatus of ganglion cells and amacrine cells. The histochemical reaction is positive also in the rough surfaced endoplasmic reticulum of some horizontal cells. The highest activity is seen in the internal plexiform layer; because of artifacts caused by the diffusion of the enzyme, a clear demonstration of relation of the positivity to one or the other regular components of this layer, however, is not possible. Myelinated fibers which exhibit acetylcholinesterase activity and are most probably efferent are found in the internal plexiform layer. In the retinal nerve fiber layer and in the optic nerve only a few fibers show a positive reaction.