S. Iurato

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.

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.

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.

Verbindungskomplexe An Zellen Der Reissner-Membran In Gefriergebrochenen Präparaten

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.

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.

Zellverbindungskomplexe im Limbus spirale

SummaryThe spiral limbus of the chinchilla inner ear was investigated using the freeze-fracture method.In the replica we observed that a) the intercellular space between the epithelial cells of the spiral limbus (interdental cells and inner sulcus cells) is completely sealed from the endolymphatic space by extense tight junctions, b) the epithelial cells are joined to each other by gap junctions, as well as the cells of the perilymphatic space.Tight junctions seal the intercellular space of an epithelium towards an adjoining lumen, gap junctions represent an area of electrotonical and metabolical communication of cells without participation of the intercellular space.From these findings in accordance with previous investigations of the vascular stria, the Reissner-membrane, and the organ of Corti we conclude, that in the inner ear the tight junctions occur independently on location and function of the single epithelium and that they play a role in the maintenance of the endocochlear potential and the high potassium concentration gradient between endolymph and perilymph.The presence of numerous and extense gap junctions between the cells of the perilymphatic space is similar in the vascularised areas of the cochlear duct. A continuous supply of cells of the individual tissue seems to be maintained as well as its participation at the homoeostasis of the surrounding liquid.

Gap junctions zwischen den Stützzellen des Corti-Organs

SummaryInvestigation carried out on the inner ears of ten chinchillas by use of the freeze-fracture-method.The replicas demonstrate gap junctions in the area of contact of apposed supporting cells. They are located in the upper portion of the cells near to the reticular membrane and—mainly —at the cells body. Furthermore they are visible between processes of the cells of Deiters, surrounding the axons partly.