Tegmentum Vasculosum Research Articles

Ultracytochemical Localization of Na+, K+-ATPase Activity in the Tegmentum Vasculosum of the Developing Chick Cochlea

We studied the morphological changes and the precise localization of Na+, K+-ATPase activity in the developing chick tegmentum vasculosum (TV) with a cytochemical method utilizing K+-p-nitrophenylphosphatase (K+-NPPase). At stage 37, epithelial folds (lamellae) were relatively well developed, and the light and the dark cells were clearly identified. At stage 41 to 42, Na+, K+-ATPase activity appeared in the folded cytoplasmic processes of the dark cells which interdigitated with those of the light cells. The present results indicate that the TV is involved in the production of the cochlear endolymph prenatally (at least up to stage 41), and that the dark cell plays a central role in the maintenance of the ionic composition of the endolymph.

Ultracytochemical localization of Na+, K+-ATPase Activity in the tegmentum vasculosum of the developing chick cochlea

We studied the morphological changes and the precise localization of Na+, K(+)-ATPase activity in the developing chick tegmentum vasculosum (TV) with a cytochemical method utilizing K(+)-p-nitrophenylphosphatase (K(+)-NPPase). At stage 37, epithelial folds (lamellae) were relatively well developed, and the light and the dark cells were clearly identified. At stage 41 to 42, Na+, K(+)-ATPase activity appeared in the folded cytoplasmic processes of the dark cells which interdigitated with those of the light cells. The present results indicate that the TV is involved in the production of the cochlear endolymph prenatally (at least up to stage 41), and that the dark cell plays a central role in the maintenance of the ionic composition of the endolymph.

Localization of K+-NPPase Activity in the Developing Tegmentum Vasculosum of the Chick Cochle

Localization of K+-NPPase Activity in the Developing Tegmentum Vasculosum of the Chick Cochle

Immunocytochemical and quantitative studies of Na +,K +-ATPase distribution in the developing chick cochlea

Immunocytochemical methods were used to examine cryosections of the embryonic and neonatal chicken cochlea in order to study the histological distribution of the Na +,K 4-ATPase molecule during maturation. In complementary studies the Na +,K +-ATPase capacity of microdissected freeze-dried substructures of the cochlea was determined fluorometrically. The dark cell of the tegmentum vasculosum exhibited intense immunochemical staining of the convoluted basolateral infoldings. The adjacent light cells demonstrated very little staining. The plasma membrane of the hair cell was also stained as were the first order auditory neurons, including the cell soma. The homogene cells and the supporting cells were unstained. The dark cell was only lightly stained with the antibody at stage 45 but became more intense and selective by the seventh postnatal day. The other cells of the cochlear duct exhibited specific immunofluorescent staining of their plasma membranes from stage 45 onwards and the fluorescent intensity did not change. The tegmentum vasculosum exhibited very high activities of the Na +,K +-ATPase enzyme relative to the other structures of the cochlea. Furthermore, a pronounced gradient of enzymatic activity was detected longitudinally. The proximal tip (or high-frequency end) had a sixteen-fold greater capacity for Na +- and K +-dependent ATP hydrolysis relative to the distal tip (or low-frequency end). The appearance of this enzyme in the tegmentum vasculosum during the development of the cochlea paralleled the known rate of improvement in hearing thresholds.

Localization of Na+, K+-ATPase activity in the tegmentum vasculosum of the chick cochlea.

We studied the localization of Na+, K+-ATPase activity in the chick cochlea, utilizing a cytochemical method of K+-p-nitrophenylphosphatase (K+-NPPase), and found that the enzyme activity was limited to the dark cells of the tegmentum vasculosum (TV). Our present results indicate that the dark cells of the TV play an essential role in the maintenance of the ionic composition of the cochlear endolymph.

Ultrastructural and electrophysiological maturation of the chick tegmentum vasculosum

We have examined the ultrastructural and electrophysiological events associated with the embryonic development of the tegmentum vasculosum, the ion-transporting epithelium in the chick cochlear duct. The cytodifferentiation of the light and dark cells in the epithelium from embryonic day 6 through post-hatching day 7 was studied with transmission electron microscopy. The predominant ultrastructural change in the developing tegmentum vasculosum was the elaboration of the complex basolateral infoldings on the dark cells from embryonic day 11 through post-hatching day 7. The relationship between the development of the endocochlear transepithelial electrical potential difference (PD) and the cytodifferentiation of the tegmentum vasculosum was examined with in vitro studies. Microelectrode impalements of the scala media showed that the positive endocochlear PD was first detectable on embryonic day 20 but did not reach a mature value of +16 mV until post-hatching day 7. Maturation of the endocochlear PD paralleled the time during which the dark cells in the tegmentum vasculosum displayed the most extensive increase in basolateral infoldings. This correlation suggests that the development of the endocochlear PD may result from an increase in the number of Na +-K + pump sites located on the basolateral infoldings of the dark cells.

A freeze-fracture study of intercellular junctions between various kinds of epithelial cells surrounding common endolymphatic space in the hearing organ of the chick.

Intercellular junctions between various epithelial cells in the hearing organ (basilar papilla) of the chick were studied with the freeze-fracture technique. The effects of hypertonic solutions on the intercellular junctions were also examined. The basilar papilla of the chick is primarily composed of hair cells and supporting cells in the neuroepithelium, specialized columnar cells (TMC) which attach to the tectorial membrane, and light cells (LC) and dark cells (DC) in the tegmentum vasculosum. All of these epithelial cells surround a common endolymphatic space. The tight junctions between hair and supporting cells, and those between adjacent supporting cells in the neuroepithelium are 0.1--0.3 micrometer in depth and display the usual network of branching and anastomosing strands of shared intramembrane proteins. The tight junctions in the tegmentum vasculosum have the same structure as in the neuroepithelium. In contrast, the tight junctions between the TMCs are extremely well developed. They are 1--2 micrometer in depth. In freeze-fracture replicas, they appear as a fingerprint pattern of unbranched parallel particulate strands, running both parallel and perpendicular to the cell surface. After exposure to hypertonic solutions, all the epithelial cells are shrunken and intercellular spaces are expanded; all tight junctions, however, are intact. Thus, tight junctions in the basilar papillae are resistant to dissociation by hypertonic solutions. The usual zonulae occuludentes in the neuroepithelium and tegmentum vasculosum are thought to prevent diffusion of endolymph through the intercellular spaces of epithelial cells. However, the tight junctions on the TMCs may function not only as a diffusion barrier, but also provide structural support to the cells anchoring the tectorial membrane which receives mechanical forces induced by the vibration of the basilar membrane. Extensive gap junctions are found between all the supporting cells (supporting cells in the neuroepithelium, TMCs, and LCs in the tegmentum vasculosum) surrounding the endolymphatic space.

Ultrastructure of the Turkey’s Basilar Papilla and the Damping Elements in the Scala Media

The ultrastructure of the turkey’s inner ear was investigated by use of scanning and transmission electron microscopes. It was shown that hair cells of the basilar papilla are separated from each other by microvilli of the supporting cells. Organized compartments in the lower surface of the tectorial membrane of the turkey are arranged in polarized fashion as are the hair bundles.Kinocilia were not idenified in the hair bundles examined in this study. Well-organized filamentous elements were observed in the cuticular plates. The continuation of these filamentous elements into the stereocilia indicates that the theory of adjustable resistor in generating cochlear potential may be closely associated with these elements. Membrane bound homogeneous material was found in the scala media between the tegmentum vasculosum and the tectorial membrane. The presence of this homogeneous damping material is believed to be essential in offsetting the sensitivity and enhancing the time resolution ability of the relatively short avian cochlea.

Cochlear potentials of the pigeon inner ear recorded with microelectrodes.

The CM-intensity function (i.e. the relation between the amplitude of the cochlear potential (CM) and the sound pressure level) of the avian ear has previously been shown to deviate from the mammalian ear with respect to the slope of the linear part of the function. The lower slope values found in the perilymphatic space of the avian ear have been interpreted to indicate a damping influence of the tegmentum vasculosum on the mechanical vibration of the basilar membrane. In this study the CM-intensity function has been examined on either side of the tegmentum vasculosum of the pigeon ear using microelectrode technique. The slope of the linear part of the CM-intensity function in scala vestibuli was found to be a function of the sound frequency approaching unity at higher frequencies. In ductus cochlearis the slope of the linear part of the CM-intensity function was close to unity at most frequencies except the best frequency for the electrode position. At this frequency (3-4 kHz) the slope value was low. These findings from the ductus cochlearis are similar to findings in scala media of the mammalian ear. Thus the influence of tegmentum vasculosum on CM in scala vestibuli may be due to passive electrical properties of the tissue and not to the mechanical vibration of the basilar membrane.

Specialized Epithelia in the Avian Labyrinth (Its Distribution and Ultrastructure)

In recently years the distribution of the non-sensory specialized epithella in the inner ear has been interested among otologists. Increased understanding of the problem dealing with the fluid transport within the endolymph has been obtained these studied. To our knowledge, however, the distribution of the avian specialized cells in the inner ear has not been described adequately. In addition, ultrastructural characteristics of the osmiophilic(dark) cells in the avian labyrinth were not clearly demonstrated. Therefore, the specialized epithlia in the avian labyrinth should be further investigated and the nature of their function defined.To demonstrat this, pigeois were investigated using phase and electron-microscopy. The specialized cells(dark and light cells) were distributed in the crlstae ampullaris, the tegmentum vasculosum of the lagena which is analogous to the stria vascularis in mammals, the saccule, the otolith lagena, the utricle and the crista negletica.

Distribution and properties of ATPase activities in the cochlea of the chicken

1. 1. The properties and distribution of an ouabain sensitive Na +-K +-ATPase system in the cochlear structures of the chicken were investigated with ultramicrochemical techniques. 2. 2. The properties of this enzyme system are in good agreement with those found in other tissues including the stria vascularis. 3. 3. The enzyme system was present in very high activity and appeared to be predominantly located in the tegmentum vasculosum. 4. 4. The agreement between the activities and properties of the Na +-K +-ATPase system in the tegmentum vasculosum of the chicken cochlea and the stria vascularis of the mammalian cochlea suggests that the tegmentum vasculosum may play the same essential role in the maintenance of the cochlear cation gradients and the cochlear potentials as the stria vascularis.

Ultrastructure of the tegmentum vasculosum and transitional zone.

Ultrastructure of the tegmentum vasculosum and transitional zone.

Cochlear function and sodium and potassium activated adenosine triphosphatase.

The maintenance of the cation gradients between endolymph and perilymph in the cochlea requires the operation of a cation pump. An adenosine triphosphatase system activated by sodium and potassium is present in high activity in the cochlear membranes (tegmentum vasculosum and stria vascularis). The cochlear microphonic potential is inhibited by perilymphatic perfusion of ouabain and erythrophleine. Since the microphonic potential depends on the high concentration of potassium ions in the endolymph, our findings strongly suggest the operation of an adenosine triphosphatase cation pump system activated by sodium and potassium, in the generation of cochlear cation gradients.