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J A Merchan

Publications and source records attributed to J A Merchan.

13 recordsLinked to original sources
PubMed1997

Structure of glycogen particles in organ of Corti's outer hair cells in three rodent species.

Organ of Corti's outer hair cells are one of the few cell types in mammals to contain large cytoplasmic glycogen stores, and the only one in the adult auditory receptor. Previous reports on the structure and distribution of glycogen in the adult organ of Corti were mainly based on light microscopy histo- and cytochemical methods, and the scare EM studies on the topic relied on techniques which were not sensitive or specific enough. Furthermore, it has been reported that glycogen particles are not present in outer hair cells of all species. A first goal of the present study was to describe the ultrastructure of glycogen stores in organ of Corti's outer hair cells in Guinea pig, rat, and mouse, using the periodic acid-thiocarbohydrazide-silver proteinate method. In addition, differences in the subcellular and cochleotopic distribution of this substance were analyzed. In the adult organ of Corti only the outer hair cells contain glycogen stores. Present throughout their cytoplasm, these deposits appear either as single beta particles, or as aggregates of these, forming alpha particles. Though most alpha particles are round, some appear long and conspicuously straight in longitudinal sections of those cells near the apex of the cochlea, and they seem to be apposed to some filamentous structure. On the other hand, when the cells are sectioned transversely the larger aggregates of glycogen particles follow a curved course. Since outer hair cells of the apical region of the cochlea contain a bundle of contractile microfilaments, our results suggest that glycogen is associated with the contractile apparatus of these cells. This hypothesis is in good accordance with previous experimental data which suggest that glycogen is used as energy source for the contractile movements of outer hair cells.

Aging↗
PubMed1990

Lectin staining of saccharides in the normal and hypothyroid developing organ of Corti.

Lectin staining has been used to detect mono- and oligosaccharides in normal and hypothyroid developing organs of Corti in the rat. Eight developmental stages were studied (1, 5, 8, 10, 15, 20, 50 and 60 days after birth). Congenital hypothyroidism was induced by oral administration of propylthyouracil to pregnant rats. Labelling of the tectorial membrane with 3 lectins, Ulex europaeus agglutinin-I (UEA-I), Lens culinaris agglutinin (LCA) and Ricinus communis agglutinin-I (RCA-I) showed no significant differences between normal and hypothyroid animals. Staining with peanut agglutinin (PNA) showed that the hypothyroid adult tectorial membrane (but not the normal one) possesses the disaccharide galactose + N-acetyl galactosamine. Phaseolus vulgaris agglutinin-L (PHA-L) labels the whole tectorial membrane in both groups of animals, but the staining is more intense in the hypothyroid one for a narrow band of oligosaccharide located just between the tectorial membrane and the underlying organ of Kölliker. Both soybean agglutinin (SBA) and succinylated wheat germ agglutinin (WGA) stain the tectorial membrane as well as the cytoplasm of the cells constituting the inner portion of the organ of Kölliker; this latter feature disappears in the normal animals about the 8th postnatal day, but it is abnormally preserved until the 60th postnatal day in the hypothyroid ones. In the adult hypothyroid animals, 3 of the lectins (LCA, PHA-L and WGA) stain extracellular conglomerates located under the synaptic pole of the outer hair cells.

Animals↗
PubMed1990

The effect of hypothyroidism on the development of the glycogen content of organ of Corti's hair cells.

The density of glycogen particles in organ of Corti's sensory cells was measured to determine the effect of congenital hypothyroidism upon the normal development of this energy source. This density in both normal and hypothyroid inner hair cells remains in low values from birth to adulthood. On the other hand, that of normal outer hair cells undergoes a great increase between the 10th and the 20th postnatal days, coinciding with the maturation of both the efferent innervation of these cells and the tuning properties of the auditory receptor. The glycogen stores of the hypothyroid outer hair cells do not show any significant increase from birth to adulthood. This latter fact suggests that the congenital hypothyroidism restrains the development of an important energy source of outer hair cells, most surely disturbing the physiological processes relying on glycogen metabolism.

Animals↗
PubMed1990

Localization of anionic sulfate groups in the tectorial membrane.

Colloidal iron hydroxide (CIH) staining demonstrates the existence of anionic sulfate groups of glycoconjugates associated with several constituents of the tectorial membrane (TM). In the adult animal, labelling in the main body of the TM appears as long, electron-dense patches surrounding type A fibrils which show alternating stained and unstained zones. On the other hand, labelling of the fibrils of the matrix of the TM appears as single, CIH particles with no special arrangement. Some of the structurally distinct regions of the TM are also labelled (limbal zone, Hensen's stripe and inner portions of the cover net), while others are not (marginal band and outer portions of the cover net). Staining of type A fibrils in the major TM is already present in newborn animals; while, both the outermost region of the TM closest to the cells of the organ of Kölliker and the minor TM are not labelled. The implications of these distributions of sulfated glycoconjugates for the electrochemical properties of the TM are discussed.

Animals↗
PubMed1990

Two different secretion mechanisms in the inner ear's interdental cells.

Fixation with a mixture of tannic acid and glutaraldehyde reveals a darkly stained substance in the intercellular clefts between juxtapposed interdental cells, where it is included by pynocytotic vesicles. Over the interdental cells, similar-sized vesicles (35-45 nm) are present in clear spaces of the amorphous layer of the limbal portion of the tectorial membrane. Some images suggest that they may be secreted through small disruptions of the membrane of the interdental cells' microvilli. In addition, a TA-unstained, amorphous material is present inside both basal ducts and apical cavities of the interdental cells, thus suggesting another secretory route from the basal region of the interdental cells towards either the endolymph, or the tectorial membrane. These two secretion processes coexist in a single interdental complex, and the two secretion products may be involved in the turnover of the adult tectorial membrane and/or the secretion of some component of the endolymph.

Animals↗
PubMed1987

Regional specialization of the cell coat in the hair cells of the organ of Corti.

The anionic sulfated groups of the cell coat glycoconjugates were studied in sensory and supporting cells of the organ of Corti with the colloidal iron hydroxide technique of Mowry, modified by Seno et al. [(1985) Histochemistry 82, 307-312]. This technique specifically stains the apical (endolymphatic) surface of both inner and outer hair cells. As this is the area at which the influx of potassium into the sensory cells takes place, the accumulation of negative charges in this location may be a mechanism to concentrate cations (mainly potassium) close to this portion of the hair cell membrane.

Animals↗
PubMed1986

Tannic acid staining of the cell coat of the organ of Corti.

Tannic acid staining of the cell coat of the organ of Corti shows a deep asymmetry between the endo- and the perilymphatic surfaces, the former being 6 times thicker. This fact may be related to a barrier mechanism against potassium-induced cell damage. Horizontal cross-links between stereocilia were heavily stained, but vertical ones were not preserved, thus suggesting they are not glycoconjugates.

Animals↗
PubMed1986

Distribution of primary cochlear afferents in the bulbar nuclei of the rat: a horseradish peroxidase (HRP) study in parasagittal sections.

HRP was injected into the cochleae of 25 young albino rats in order to trace the primary afferents to the bulbar cochlear nuclei. Besides the classic V-shaped pattern and unconnected with it, HRP labelling revealed two plexuses stemming directly from the axons of the cochlear root. The plexuses cover the posterior area of the posteroventral cochlear nucleus (posterior plexus) and the anterolaterodorsal area of the anteroventral cochlear nucleus (anterior plexus). The fibres giving rise to these two plexuses were previously grouped in two bundles which have been called the posterior and anterior bundles, respectively. The origin of the anterior bundle is typically seen with the fibres stemming out at right angles; the origin and course of the posterior bundle, which characteristically cross over, is also a typical feature.

Afferent Pathways↗
PubMed1985

Distribution of primary afferent fibres in the cochlear nuclei. A silver and horseradish peroxidase (HRP) study.

Horseradish peroxidase, when injected intracochlearly, is transported transganglionically to the brain stem cochlear nuclei, thus providing an excellent method for tracing the central projection of the spiral ganglion neurons. Silver impregnation using the Cajal-de Castro method, which stains axons even when inside the bone, was used as a reference technique. The combination of both procedures led to the following conclusions. Primary cochlear afferents are found only in the ventral zone of the dorsal cochlear nucleus. In this area they cover the deep and fusiform cell layers. The molecular layer shows no HRP label. The higher concentration of primary cochlear afferents in the ventral cochlear nucleus appears in its central zone; wide areas in this nucleus are not labelled at all. A thin bundle of primary cochlear afferents runs parallel to, and beneath, the granular region.

Afferent Pathways↗
PubMed1980

Ultrastructure of the oviductal mucosa of the rat. III. Basal and peg cells.

In an E.M. analysis of the rat oviduct the authors report the morphology of the so-called indifferent basal cells and peg cells. The hallmark of the former are desmosomes and clear cytoplasm; these elements may detach themselves from the basal membrane, migrating towards the lumen and showing prominent ciliogenesis. Peg cells appear to be the morphological image of necrobiotic cells, either ciliatd or secretory.

Animals↗
PubMed1980

Morphology of Hensen's cells.

The cochleae of ten guinea-pigs were studied by transmission electron microscopy, scanning electron microscopy and optical microscopy, using specific techniques for staining fats. The study of Hensen's cells showed the existence of prominent lipid droplets in the apex and the third coil of the cochlea. Similar images were not found in the basal coil. Lipids appear to be expelled into the endolymphatic space. The significance of these findings is discussed with respect to the geometry of the lateral anchorage of the tectorial membrane and to the possibility that Hensen's cells represent a modulation mechanism in the transmission of mechanical energy.

Animals↗
PubMedDate not supplied

Surgical trauma to the cochlea results in reversible damage to spiral ganglion type I neurons.

Type I neurons are reversibly damaged when the cochlear bony wall is opened. The reversibility is indicated by the absence of neuronal loss, as demonstrated by quantification of the spiral ganglion neuronal population. Reversible damages included ultrastructural signs of excessive ion and water influx into the type I neuron cytoplasm, whose functional implications must be investigated in the future.

Animals↗