E. Reale

Intercellular junctions in the vascular stria and spiral ligament

The junctional complexes in the vascular stria and spiral ligament of the chinchilla inner ear have been studied using the electron microscope with freeze-fracture technique. The intercellular spaces of the vascular stria are sealed towards the endolymph by the zonulae occludentes “intermediate to tight” of the marginal cells and towards the perilymph by the zonulae occludentes “very tight” of the basal cells. All the cells of the vascular stria and spiral ligament have their cytoplasms in direct communication, which is mediated by numerous gap junctions. The significance of the junctional complexes of the vascular stria probably is connected with the unique ionic composition of the cochlear endolymph and with the maintenance of steep solute gradients by active transport in the stria.

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.

Intercellular junctions and other membrane specializations in developing spinal ganglia: a freeze-fracture study.

Intercellular junctions and other membrane specializations of neuroblasts and satellite cells were studied in spinal ganglia of chick embryos at the 4th, 10th, and 16th incubation days using the freeze-fracture technique. At the 4th day neuroblasts are closely arranged and connected by gap junctions. At the 10th day, instead, satellite cells appear interposed between neuroblasts so the gap junctions previously joining the latter are no longer evident. These temporary junctions probably play a role in cell differentiation and intercellular adhesion. Together with adhering junctions, gap junctions might maintain the cell organization of the ganglionic rudiment, which at the 4th day still lacks connective tissue. At the 10th day adjacent satellite cells display on their split plasma membrane small gap junctions, short, usually isolated strands recalling those composing zonulae occludentes, and orthogonal particle assemblies. These two latter specializations are still evident at the 16th day. The possible significance of these specializations is briefly discussed.

Cholinesterase activity in spinal ganglia neuroblasts: a histochemical study at the electron microscope.

Cholinesterase activity was localized in spinal ganglia of chick embryos with Karnovskys method at the electron microscope. Controls with eserine, BW 284 C 51, and iso-OMPA were carried out. Acetylcholinesterase activity was present at 3 days of incubation. This enzymatic activity was evident in the following sites: perinuclear cisterna of some of the probably undifferentiated cells; perinuclear cisterna and granular endoplasmic reticulum of some of the mitotic cells; perinuclear cisterna and granular endoplasmic reticulum of transitional cells, primitive and intermediate neuroblasts, pseudo-unipolar nerve cells; along the perikaryal plasma membrane and axolemma. In spinal ganglion neuroblasts acetylcholinesterase activity appeared long before synaptic function onset and, therefore, seems to be independent from it. Nonspecific cholinesterase activity was localized within the perinuclear cisterna and granular endoplasmic reticulum of the satellite cells. In neuroblast Golgi complex vesicles and dense bodies a positive reaction was evident, which perhaps is partly due to a nonspecific esterasic activity.

Fracture faces of the junctional complexes in the reticular membrane of the organ of corti

The junctional complexes in the reticular membrane of the organ of Corti have been investigated in chinchilla inner ear by the freeze-fracture method. Extremely developed zonulae occludentes were observed where the supporting cells contact each other and the sensory cells. These junctions can be considered “very tight” and completely seal off the tunnel of Corti, Nuels space and the outer tunnel from the endolymph, as observed by investigations carried out by using tracers. The zonulae occludentes between Hensens cells are always uninterrupted but considerably lower than among supporting and sensory cells.

Acetylcholinesterase Activity in the Vestibular Sensory Areas

The localization of AChE activity was investigated in the cristae ampullares, utricle and sac-cule of chinchilla inner ear with the electron microscope by Karnovskys method. The reaction was positive on the plasma membrane of the efferent nerve fibres and endings. The reaction product filled the synaptic gap between these endings and the afferent dendrites and nerve chalices. The reaction product was absent at the junction between the hair cells and the afferent nerve endings and chalices. The controls indicated that the reaction was due to AChE activity.

The localization of acetylcholinesterase activity in the spinal ganglia of the adult fowl studied by electron microscope histochemistry

SummaryAChE activity was localized in spinal ganglia of adult fowls at the electron microscope level using Karnovsky’s method. Controls with BW 284 C 51 were carried out. In the neuronal bodies, AChE activity was evident within the rough-surfaced cisternae of the endoplasmic reticulum, including the perinuclear cisterna and the subsurface cisternae, and sometimes in the innermost cisternae of the Golgi complex. AChE activity was also demonstrated along the axolemma and associated with smooth-surfaced vesicles and tubules in the initial segment of the axon, in all the ganglionic myelinated fibers examined by serial section analysis and in more than half of the ganglionic unmyelinated fibers examined by this method. In the myelinated fibers the reaction product appeared more abundant at the level of the nodes of Ranvier than in the internodal segments. Both in the myelinated and unmyelinated fibers a considerable quantitative variability of reaction product was observed among the various sections of the same fiber. These results were compared with those previously obtained in the spinal ganglia of the chick embryo using the same histochemical method.

Lysosomes in normal and degenerating neuroblasts of the chick embryo spinal ganglia

SummaryLysosomes 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.

Histochemical Localization of Acetylcholinesterase Activity in the Cochlear and Vestibular Ganglion Cells

The localization of AChE activity was investigated in the cochlear and vestibular ganglion cells of the chinchilla inner ear with the electron microscope by Karnovskys method. The reaction product was localized within the rough-surfaced cisterns of the E. R., including the perinuclear cistern, and in some cisterns of the Golgi complex. In a few myelinated nerve fibres and in most of the unmyelinated ones the reaction product was present along the axolemma. The reaction product was absent in the satellite and Schwann cells. The controls indicated that the reaction was due to AChE activity.

Freeze-fracture study of the cell junctions in the utricle and saccule.

The maculae sacculi and utriculi of the chinchilla vestibular labyrinth have been studied by freeze-fracture method. In the replicas extensive zonulae occludentes have been found between sensory and supporting cells at the endolymphatic surface. Gap junctions are located between the supporting cells. Some intramembranous specializations of the synaptic regions are described in both types of the sensory cells.