Biomedical subjects

B A Schulte

Publications and source records attributed to B A Schulte.

At least 19 recordsLinked to original sources

PubMed1999

Immunohistochemical localization of Ca2+/Calmodulin-dependent protein kinase IV in outer hair cells.

A smooth membrane system consisting of subsurface cisternae (SSC) underlies the lateral plasmalemma of auditory outer hair cells (OHCs). The SSC contain Ca-ATPase and are regarded as an intracellular Ca2+ reservoir like the sarcoplasmic reticulum of myocytes. Recently, it has been demonstrated that Ca-ATPase activity in sarcoplasmic reticulum is regulated by Ca2+/calmodulin-dependent protein kinases (CaM kinases). Here we investigated the presence of CaM kinases in OHCs and their possible association with the SSC. Inner ears collected from adult gerbils and from neonates at 2-day intervals between 0 and 20 days after birth were immunostained with antibodies specific for different CaM kinases. A polyclonal antiserum against CaM kinase IV yielded a strong immunostaining reaction along the lateral wall of OHCs. The staining appeared after the tenth postnatal day and continued into adulthood. No other site in the inner ear, including cochlear inner hair cells and vestibular hair cells, was reactive. The kinase's apparent association with the SSC strongly supports its involvement in intracellular Ca2+ homeostasis and suggests a role in regulating the OHCs' slow motile responses.

Aging↗

PubMed1999

Exogenous 17beta-estradiol blocks alpha and mu but not pi class glutathione S-transferase immunoreactivity in epithelium of Syrian hamster vas deferens.

Members of the glutathione S-transferase (GST) family of detoxification enzymes play a role in chemotherapy resistance in certain cancers but have not been directly implicated as agents whose absence may predispose tissues to hormonally induced tumorigenesis. Here we report the development of a polyclonal antiserum to a hamster mu class GST, and immunohistochemical analysis of alpha, mu, and pi class GSTs to study the effects of hormone treatment on their expression in reproductive tract tissues of male golden Syrian hamsters. These animals develop leiomyosarcomas in the vas deferens after treatment with testosterone propionate (TP) and 17beta-estradiol (E2). High levels of all three GST classes were detected throughout the reproductive tract epithelium of control animals. In 100% of the experimental animals, 4 weeks of treatment either with E2 alone, or with E2 plus TP promoted a complete loss of immunostaining for alpha and mu class GSTs, but not for pi class GSTs, only in the epithelial lining of the vas deferens. In contrast, treatment with TP alone resulted in moderate hyperplasia of smooth muscle in the proximal vas deferens, with no cellular atypia and no changes in immunoreactivity of any of the GST classes. The consistent and site-specific nature of these results strongly suggests a functional role for GSTs in hormonally induced carcinogenic process. (J Histochem Cytochem 47:91-98, 1999)

Animals↗

PubMed1998

Glutathione S-transferase in hormonal carcinogenesis.

Treatment with testosterone propionate (TP) and diethylstilbestrol (DES) or TP and estradiol (E2) for 8-9 months causes development of leiomyosarcomas in the vas deferens or uterus of Golden Syrian hamsters at a frequency of 100%. In males, treatment with estrogens alone results in renal tumors, fatal within 6 months. No leiomyosarcomas have been detected after treatment with estrogens alone, perhaps due to this high mortality rate. In tissue culture, treatment with the glucocorticoid (GC) triamcinolone acetonide (TA) results in an increased expression of a mu-class glutathione S-transferase (GST) (hGSTYBX). We have characterized this induction as a secondary response, i.e. requiring new protein synthesis. Here we describe homologies to known transcription factor-binding sites in the hGSTYBX promoter which may be involved in the induction event. hGSTYBX is a member of a superfamily of detoxification enzymes, induced by genotoxic compounds and reactive oxygen species (ROS). We also describe the effects of several known inducers of other GST family members on hGSTYBX. While implicated in many chemotherapeutic-resistant tumors, GST enzymes have not yet been characterized as a functional agent in hormonal carcinogenesis. This latter possibility is the focus of our investigations. To study the effects of hormone treatment on GST levels in vivo, we have developed a polyclonal antibody to hGSTYBX, and conducted immunohistochemistry on tissues from control and treated animals. Treatment with TP and E2 causes a loss of hGSTYBX expression in the epithelium of the vas deferens. We hypothesize that the loss of this protective enzyme leaves the cells vulnerable to the genotoxic effects of estrogen or estrogenic metabolites.

Animals↗

PubMed1998

Cytologic evidence for mechanisms of K+ transport and genesis of Hensen bodies and subsurface cisternae in outer hair cells.

UNLABELLED: A system commonly termed the tubulocisternal endoplasmic reticulum (TCER), but designated here the canalicular reticulum (CR), occurs selectively in ion-transporting epithelia, in which it is interpreted as facilitating the transcellular diffusion of ions. Mechanoelectrical transduction in the cochlear outer hair cells (OHCs) depends on the apical influx and the subsequent basolateral efflux of K+. Cytologic structures that possibly mediate K+ transport in gerbil OHCs were investigated here. METHODS: Cochleas were fixed primarily with glutaraldehyde and secondarily with reagents for demonstrating TCER or were fixed with a ferrocyanide-osmium tetroxide solution to preserve intracellular membranes. The distribution of membranous structures retained with these techniques was examined by using electron microscopy. RESULTS: Secondary fixation with osmium tetroxide-ferrocyanide permitted ultrastructural demonstration in OHCs of increased numbers of Hensen bodies and newly detected membranous systems, including CR, linear cisternae, small clusters of cytosolic vesicles and complexes of canaliculi, segmented cisternae, and mitochondria. CR filling an apical stratum beside and below the cuticular plate and contacting laterally the uppermost subsurface cisternae (SSC) was situated to sequester and transport the apical K+ influx that attends the acoustically generated receptor potential and the silent current. The close association of CR with numerous, highly developed Golgi bodies exclusively in the apex of the cell suggested genesis of CR from Golgi cisternae. Nonbranching, linear cisternae occupied a lower cell stratum and spread from CR laterally to a more inferior region of the SSC. Small clusters of vesicles in the central cytosol resembled Hensen bodies in their envelopment by branching canaliculi and segmented cisternae in close association with mitochondria. Viewing the vesicles in Hensen bodies and the small clusters as functioning like most other cytoplasmic vesicles in transport of cell membrane permitted the interpretation that these vesicles move nascent membrane from the canalicular-mitochondrial complex to the SSC. Other small clusters of vesicles contacted the innermost layer of the SSC, often at cisterna-depleted foci in which the vesicles appeared to either replenish the SSC or arise in the course of its turnover. Proximity of multivesicular bodies and lysosomes to small vesicle clusters in foci of depleted SSC implicated the lysosomes in digesting vesicles released from the SCC. Populations of unique, large, lysosome-like bodies and of small, dense bodies in the upper cytosol of OHCs appeared to be involved in different catabolic pathways mediating the turnover ofSSC, CR, and other structures. CONCLUSIONS: Cochlear OHCs contain previously unrecognized membranous organelles that facilitate ion transport and presumably contribute thereby to mechanoelectrical transduction. Vesicles in small clusters and Hensen bodies arise from complexes of canaliculi, cisternae, and mitochondria and contribute membrane to the genesis of the SSC.

Animals↗

PubMed1998

Chemical signals in the reproduction of Asian (Elephas maximus) and African (Loxodonta africana) elephants.

Asian (Elephas maximus) and African (Loxodonta africana) elephants exhibit polygynous mating that involves female choice of mates and male-male competition for access to females. Chemical signals mediate intersexual and intrasexual interactions associated with reproduction. The need for reliable and honest signals is accentuated by the markedly different social structure of adult males and females. Adult female elephants live in matriarchal herds consisting of a dominant female and several generations of offspring. Adult males are solitary or travel with other males except during breeding periods. Because females have a long 16-week oestrous cycle with a brief 1-week receptive period and a 4-5 year interval between births, a sexually active female is a limited resource. Asian elephant females advertise a forthcoming ovulation by releasing (Z)-7-dodecen-1-yl acetate in their urine during the preovulatory period. African elephants probably produce a sex pheromone as well. Females regularly contact the ano-genital region of other females and show heightened chemosensory responsiveness to urine during the follicular phase. The physiological impacts of this ability to detect reproductive condition (e.g. possible synchronizing or suppressing of oestrus) are uncertain. Males experience an annual period of heightened aggressiveness and highly elevated testosterone concentrations known as musth. Males secrete fluid copiously from their temporal gland and dribble strongly odoriferous urine during musth. Females appear to prefer musth males as mates, and captive Asian females exhibit greater chemosensory responses to urine from males in musth than not. Males in musth are competitively dominant to all other males, even those larger than themselves. Nonmusth males avoid males in musth, and captive Asian bulls show greater interest in musth than nonmusth urine. In captivity subordinate Asian females back away from musth secretions, and females with calves sometimes display protective behaviour. Clearly, chemical signals play an important role in communication by elephants between and within the sexes. Further work is needed to identify more of these chemical messengers and to understand their complete function in mediating reproductive interactions in the elephant social system.

Animals↗

PubMed1998

Evidence for a medial K+ recycling pathway from inner hair cells.

K+ effluxed from outer hair cells and their nerves is thought to flow laterally to strial marginal cells for recycling into scala media. Observations reported here provide evidence that K+ effluxed from inner hair cells and inner radial nerves travels medially through border cells, inner sulcus cells (ISCs), limbal fibrocytes and interdental cells (IDCs) for return to endolymph. Morphologic features of ISCs in the medial route resembled those of Hensen and Claudius cells in the lateral indicating an ion transport role for ISCs like that of Hensen and Claudius cells. Na,K-ATPase in plasmalemma of IDCs testified to their capacity to resorb and transport K+ through their known gap junctions. IDCs were differentiated into three subgroups. The most lateral IDCs formed short and long columns. Long columns contacted the medialmost ISC inferiorly and the undersurface of the tectorial membrane superiorly providing thereby a potential transcellular route for K+ transit from ISCs to endolymph. Short columns faced inner sulcus below and tectorial membrane above and accordingly possessed cells with opposite polarity at the bottom and top of the column. Short columns thus appeared situated to resorb electrolytes from limbal stroma for release into inner sulcus and beneath tectorial membrane at opposite ends of the column. The central IDCs were positioned for resorbing and transporting K+ effluxing from the Na,K-ATPase-rich stellate fibrocytes which spread toward the IDCs from near the inner sulcus. The most medial IDCs lined cuplike invaginations near the attachment of Reissner's membrane and lay apposed to light fibrocytes located between supralimbal fibrocytes and the medial IDCs. Content of Na,K-ATPase and position in the K+ transport route likened the limbal stellate fibrocytes to the spiral ligament type II fibrocytes and supralimbal fibrocytes to suprastrial fibrocytes in the lateral wall. From content of creatine kinase and position in the transport path, limbal light fibrocytes appeared analogous to spiral ligament type I fibrocytes. The additional finding that limbal fibrocytes showed unchanged or upregulated Na,K-ATPase immunoreactivity in aged gerbils with strial atrophy provided further evidence for an independent medial transport route and for the survival of inner hair cells in presbyacusis.

Aging↗

PubMed1998

Na-K-Cl cotransporter expression in the developing and senescent gerbil cochlea.

Changes in the cellular expression pattern of the Na-K-Cl cotransporter (NKCC) were investigated during postnatal development and with advancing age in the gerbil cochlea. At birth, faint immunostaining for NKCC was discernable in the developing stria vascularis (StV), Reissner's membrane, interdental cells and some relatively undifferentiated cells lining the cochlear partition. Between 2 and 4 days after birth (DAB) immunostaining persisted and increased in the future interdental, inner and outer sulcus and claudius cells but then disappeared from these sites by 8 DAB. In contrast, NKCC immunoreactivity in the StV increased progressively during development and approached adult levels by 12 DAB. Immunostaining for NKCC in subpopulations of fibrocytes in the inferior portion of the spiral ligament, the suprastrial region and the spiral limbus was first detectable between 10 and 12 DAB and staining intensity reached adult levels around 16 DAB. Changes in NKCC expression with advancing age generally mimicked those previously observed for Na,K-ATPase in focal regions of atrophic lateral wall. Diminished immunostaining was first seen in the StV, presumably associated with the involution of the marginal cell's basolateral processes. Further atrophy culminated in complete loss of immunostaining in the StV and an associated down-regulation of NKCC expression in spiral ligament transport fibrocytes. The marked similarities in the developmental and age-related expression patterns of NKCC and Na,K-ATPase point to a high level of functional cooperativity between these two ion transport mediators, which together provide an efficient mechanism for generating and maintaining high K+ levels in endolymph and the endocochlear potential.

Aging↗

PubMed1998

Identification of mRNA transcripts and immunohistochemical localization of Na/H exchanger isoforms in gerbil inner ear.

Recent physiological and pharmacological studies have implicated involvement of the Na/H exchanger (NHE) in regulating inner ear ion homeostasis, but the cellular distribution of this membrane transporter remains unknown. Here reverse transcription and the polymerase chain reaction (RT-PCR) were employed to screen adult gerbil inner ears for mRNA transcripts encoding the four best characterized isoforms of NHE. PCR products spanning selected segments of NHE mRNAs were cloned and sequenced. The putative housekeeping gene NHE-1 was found to be expressed and the 459 bp product shared 98.7% amino acid homology with rat sequence. NHE-2, NHE-3 and NHE-4 cDNA transcripts likewise were detected and the PCR products shared 100, 99.4 and 88.9% amino acid homology, respectively, with their rat counterparts. In addition, the cellular distribution of NHE isoforms 1 and 3 was mapped in the gerbil inner ear by immunostaining with polyclonal antisera against rat antigens. In the cochlea, the antiserum against NHE-1 reacted strongly at the basolateral membrane of strial marginal cells as well as with inner and outer hair cells and spiral ganglion neurons. Less intense staining for NHE-1 was present in subpopulations of fibrocytes in the spiral limbus and in inferior and superior areas of the spiral ligament. In the vestibular system dark and transitional cells expressed abundant NHE-1 as did hair cells and vestibular ganglia neurons. Immunostaining with the antiserum against NHE-3 was limited to the apical surface of marginal cells in the stria vascularis. Based on these data, NHE-1 likely functions primarily to maintain intracellular pH levels in cells where it is found in high abundance. NHE-3, on the other hand, possibly participates in the vectorial transcellular movement of Na+ by strial marginal cells thus helping to maintain the extremely low Na+ level in cochlear endolymph.

Animals↗

PubMed1998

Oncomodulin is expressed exclusively by outer hair cells in the organ of Corti.

Oncomodulin (OM) is a small, acidic calcium-binding protein first discovered in a rat hepatoma and later found in placental cytotrophoblasts, the pre-implantation embryo, and in a wide variety of neoplastic tissues. OM was considered to be exclusively an oncofetal protein until its recent detection in extracts of the adult guinea pig's organ of Corti. Here we report that light and electron microscopic immunostaining of gerbil, rat, and mouse inner ears with a monoclonal antibody against recombinant rat OM localizes the protein exclusively in cochlear outer hair cells (OHCs). At the ultrastructural level, high gold labeling density was seen overlying the nucleus, cytoplasm, and the cuticular plate of gerbil OHCs. Few, if any, gold particles were present over intracellular organelles and the stereocilia. Staining of a wide range of similarly processed gerbil organs failed to detect immunoreactive OM in any other adult tissues. The mammalian genome encodes one alpha- and one beta-isoform of parvalbumin (PV). The widely distributed alpha PV exhibits a very high affinity for Ca2+ and is believed to serve as a Ca2+ buffer. By contrast, OM, the mammalian beta PV, displays a highly attenuated affinity for Ca2+, consistent with a Ca2+-dependent regulatory function. The exclusive association of OM with cochlear OHCs in mature tissues is likely to have functional relevance. Teleological considerations favor its involvement in regulating some aspect of OHC electromotility. Although the fast electromotile response of OHCs does not require Ca2+, its gain and magnitude are modulated by efferent innervation. Therefore, OM may be involved in mediation of intracellular responses to cholinergic stimulation, which are known to be Ca2+ regulated. (J Histochem Cytochem 46:29-39, 1998)

Animals↗

PubMed1997

Golgi-canalicular reticulum system in ion transporting fibrocytes and outer sulcus epithelium of gerbil cochlea.

BACKGROUND: Five types of highly specialized fibrocytes have been identified in the spiral ligament of the gerbil cochlea. Type I, II, and IV fibrocytes function in cycling back to the stria vascularis K+ effluxed from outer hair cells and nerves during auditory transduction. Thus, evidence exists for a transcellular path of K+ movement from outer sulcus cells through fibrocytes to the strial interstitial space, but a mechanism for facilitating such ion flow within the cells has not been elucidated. METHODS: The spiral ligament of glutaraldehyde-osmium tetroxide-fixed and Epon-embedded gerbil cochlea was examined by transmission electron microscopy. RESULTS: Ultrastructural examination disclosed an extensive membrane limited reticulum in the cytoplasm of type I, II, IV, and V fibrocytes of the lateral wall and in outer sulcus cells and their root processes. This system resembled the tubulocisternal endoplasmic reticulum present in some ion-transporting epithelia but appeared more to constitute a network of canaliculi and is referred to as the canalicular reticulum (CR). Many typical small Golgi complexes invariably accompanied the CR in the fibrocytes and sulcus cells, as we have found to be true of other epithelia known to contain CR and function in ion transport. Numerous mitochondria populated cytosol-containing CR. CONCLUSIONS: The data support the concept of transcellular K+ flux in type I, II, IV, and V fibrocytes and outer sulcus cells in the cochlea and lend credence to the view of CR as functioning in the movement of ions through cells. The constant and precise association of Golgi complexes with CR in the different cell types implies a functional relationship possibly concerned with biosynthesis of CR by Golgi elements, and the abundance of mitochondria near CR indicates an energy requirement for function of the reticulum or its biosynthesis.

Animals↗

PubMed1997

Increased laminin deposition in capillaries of the stria vascularis of quiet-aged gerbils.

The distribution of laminin (LA) and type IV collagen (IV-C) in the gerbil inner ear was investigated by light and electron microscopic immunohistochemistry. Changes in protein expression were assessed from birth to old age to determine the relation of these constituents to maturation of the cochlea and development of presbyacusis. The distribution of LA paralleled that of IV-C during postnatal development, and both were visualized in the basement membrane (BM) of endothelial, epithelial and spiral ganglion cells in neonatal and young adult gerbils. Immunopositive BM underlying the stria vascularis disappeared at 8-12 days after birth coincident with the development and maturation of the strial capillaries. Immunoreactivity for LA afforded an index to the thickness of the BM and was found to increase with age only in the BM of strial capillaries. At 6 months of age, occasional strial capillaries in the apex of the cochlea showed thickening of the LA-positive BM. Abnormal deposition of LA in strial capillary BM spread to lower turns and increased in prevalence with advancing age, affecting apical and basal more than middle cochlear turns. Thickening of the capillary BM appeared to precede capillary obstruction which eventuated in complete strial atrophy. Staining for IV-C in the walls of the strial capillaries did not increase with age. The data show that LA and IV-C play important roles in postnatal development of the cochlea and that LA deposition increases with age only in the BM of strial capillaries.

Aging↗

PubMed1997

Localization of organ of Corti protein II in the adult and developing gerbil cochlea.

The distribution of organ of Corti protein II (OCP-II) was assessed in the developing and mature gerbil cochlea by light and electron microscopic immunohistochemistry. In the adult cochlea, OCP-II was expressed only in certain epithelial cells which included all supporting cells of the organ of Corti, inner and outer sulcus cells and interdental cells. Inner and outer hair cells lacked immunoreactivity. The highest gold particle labeling density was seen overlying intracellular regions devoid of organelles. In the developing inner ear, OCP-II was first detected at 2 days after birth (DAB) with the strongest staining in immature Deiters, inner phalangeal and pillar cells. Immunostaining intensity increased gradually in cells lying laterally and medially to the more centrally located supporting cells and reached adult levels in all reactive cell types around 18 DAB. The results demonstrated conclusively that OCP-II is a cytosolic protein and fail to support its role as a transcription factor postulated on the basis of its homology with p15 or a role in the control of the cycle as suggested by its near-identity with p19Skp1, a cyclin A/CDK2-associated protein. The continued high level of expression in the mature cochlea argues against OCP-II's involvement in regulating the development and differentiation of epithelial cells. The protein's unique distribution and its gradual increase in expression prior to and during the onset and maturation of hearing, however, support its potential function in the recycling of K+ effluxed from hair cells and neurons back to endolymph.

Acoustic Stimulation↗

PubMed1997

Histopathologic observations of the aging gerbil cochlea.

Age-related histopathologic changes were examined in cochleas from 17 gerbils born and kept in a quiet environment until near the end of their life expectancy. Hearing loss varied greatly as did the loss of outer hair cells (OHC). Inner hair cells (IHC) were seldom missing even in cochleas with severe hearing losses. Flask- and spherical-shaped OHCs were frequently seen in the apical turn. Stereocilia were usually present and orderly on OHCs, but the tallest row of stereocilia on IHCs was often disarrayed and sometimes missing. Alterations in supporting cells were sometimes present in regions of extensive OHC loss. Although pillar cells were seldom missing, the nuclei of outer pillar cells were commonly displaced from their normal basal position. The density of radial fibers appeared similar to that in young gerbils except in the apical turn of one old ear where a marked loss of radial fibers occurred without an attendant loss of IHCs. All of the quiet-aged cochleas showed a characteristic clustering of epithelial cells lining the scala media surface of Reissner's membrane. This structural rearrangement was not accompanied by a significant decrease in the total number of cells forming Reissner's membrane and did not appear to be associated with hearing loss. The findings confirm and extend earlier work showing that several different types of cells are susceptible to histopathologic changes in old ears. The extent of histopathologic changes varied widely as did the degree of hearing loss in animals with a restricted genetic background and maintained under carefully controlled environmental conditions. It was not possible, based on these initial findings, to relate specific structural to specific functional changes in the aging cochlea. Further light and electron microscopic analysis of other regions from these aged cochleas may provide more conclusive data.

Aging↗

PubMed1997

Quantification of the stria vascularis and strial capillary areas in quiet-reared young and aged gerbils.

The area of the stria vascularis (StV) and of StV capillaries was measured in radial sections from regions corresponding to 0.5, 2, 4, 10, 20 and 40 kHz. In young gerbils, StV area ranged from 3700 to 8500 microm2 and that of individual StV capillaries from 70 to 110 microm2. The maximal StV area as well as the largest number of capillaries occurred at the 20 kHz region. In quiet-aged gerbils, the StV area also varied with frequency and was 28-67% smaller than corresponding measures in young gerbils. The decrease in StV area was statistically significant at all but the 2 and 4 kHz regions. The area of individual StV capillaries declined also (8-29%) with age even when the StV area remained near normal. Reductions in capillary area were statistically significant at the 2, 20 and 40 kHz regions. The large variance in StV radial area among aged gerbils reflects the patchy nature of strial degeneration previously observed in this species. The data agree with those of our previous studies and indicate alterations in StV capillaries are a primary cause of presbyacusis in the gerbil.

Aging↗

PubMed1997

Immunoglobulin deposition in thickened basement membranes of aging strial capillaries.

The presence of immunoglobulins in the thickened basement membrane (BM) of aging strial capillaries was investigated as a possible indicator of autoimmunity in the genesis of atypical BM. Cochleas from young and old Mongolian gerbils raised in quiet were examined by immunostaining at the light microscopic level for IgG and IgM and for the BM components laminin (La) and type IV collagen (IV-C). Another age-graded series of cochleas was stained for IgG at the ultrastructural level. No immunoreactive IgG was detected in specimens from animals less than 6 months old. In contrast, 2 of 12 cochleas from 20- to 28-month-old gerbils and 11 of 20 cochleas from gerbils 30 months or older showed positive staining for IgG in strial capillary BM. IgM was not detected at any age. At the electron microscope level, no immunoreactive IgG was detected in the stria of cochleas younger than 30 months. However, labeling demonstrative of IgG was observed in the thickened BM of some strial capillaries in all six cochleas from gerbils older than 33 months. Lysosome-like granules in endothelial cells and the superiormost marginal cells also stained for content of IgG as did fibrillar material in edematous regions in the intrastrial space. In addition to showing accumulation of IgG, the findings confirm our prior demonstration of increased La deposition in the thickened strial capillary BM of all cochleas from old gerbils. The BM alterations appear confined to strial capillaries in old gerbils, since morphological observations and immunostaining for La and IgG failed to detect changes in BMs at any other site in a wide survey of aged gerbil organs including vessels in other regions of the affected cochleas. The results point more towards the development of an age-dependent permeability to IgG selectively in strial capillaries than to autoimmunity as an explanation of the IgG in BM.

Aging↗

PubMed1997

Age-related thickening of basement membrane in stria vascularis capillaries.

Ultrastructural examination was undertaken to investigate the pathogenesis of age-related atrophy of the stria vascularis (StV). Basement membrane (BM) thickness was increased in 65-85% of strial capillaries in gerbils aged 33 months or older and often exceeded by several-fold that observed in young controls. In an early stage of thickening the BM expanded slightly around the full capillary profile, after which nodular expansions of BM encircling slender cell processes were often observed at or near one or both poles of the elliptical vessel profile. As widening progressed, the BM consisted of 2-3 layers separated by cell processes in the nodules but fewer strata elsewhere. Association of slender processes of both endothelial cells and pericytes with focal thickening outside the process suggested their participation in genesis of the capillary lesion. In later stages of atrophy, pericytes degenerated and disappeared, while endothelial cells remained intact. Eventually, thick multilayered BM devoid of endothelial cells surrounded a narrow lumen occluded by debris. The age-related change in BM in the inner ear was confined to StV capillaries. Degenerative changes in StV epithelial cells occurred apparently as a secondary consequence of the capillary lesion. The pathologic alterations in marginal cells included extrusion of blebs from the luminal surface, separation and loss of basolateral interfoldings, alteration and depletion of mitochondria and nuclear pyknosis. At the end-stage of degeneration, the StV consisted of a simple or multiple layer of squamous cells lining the scala media.

Aging↗

PubMed1997

Expression patterns of ion transport enzymes in spiral ligament fibrocytes change in relation to strial atrophy in the aged gerbil cochlea.

Fibrocytes of the lateral wall function in conjunction with the stria vascularis (StV) to mediate cochlear ion homeostasis. Age-related changes in the expression patterns of ion transport enzymes in spiral ligament fibrocytes were investigated to ascertain their relation to metabolic presbyacusis in the gerbil. Immunoreactivity of fibrocytes for Na,K-ATPase (Na,K), carbonic anhydrase isozyme II (CA) and creatine kinase isozyme BB (CK) varied among and within cochleas from aged but not from young gerbils. The variable immunostaining was related to the extent and location of StV atrophy. Age-dependent degeneration and loss of Na,K in the StV occurred predominantly in the apex and lower base and hook of the cochlea, largely sparing more central regions. Immunostaining intensity for Na,K, CK, and CA in fibrocytes changed in relation to declines in strial marginal cell Na,K initially showing upregulation followed by downregulation. Spiral ligament fibrocytes in cochleas with more than two remaining normal turns often disclosed overexpression of CK in regions of strial atrophy. Conversely, CA in such cochleas was often increased in regions of normal StV adjacent to foci of atrophic StV. Senescent cochleas with two or fewer functional turns generally contained fibrocytes with diminished CK or CA immunoreactivity in regions of atrophic StV but in isolated instances exhibited fibrocytes with enhanced staining. Heightened staining for CK in type Ia fibrocytes underlying regions of complete or partial strial atrophy indicated an increased metabolic demand in fibrocytes in response to strial insufficiency. The findings provide further support for the role of spiral ligament fibrocytes in cochlear fluid and ion homeostasis.

Aging↗

PubMed1997

Immunohistochemical localization of the Na-K-Cl co-transporter (NKCC1) in the gerbil inner ear.

We mapped the cellular and subcellular distribution of the Na-K-Cl co-transporter (NKCC) in the adult gerbil inner ear by immunostaining with a monoclonal antibody (MAb T4) generated against human colon NKCC. Heavy immunolabeling was seen in the basolateral plasma membrane of marginal cells in the stria vascularis and dark cells in the vestibular system. Subpopulations of fibrocytes in the cochlear spiral ligament and limbus and underlying the vestibular neurosensory epithelium also stained with moderate to strong intensity, apparently along their entire plasmalemma. Because MAb T4 recognizes both the basolateral secretory (NKCC1) and the apical absorptive (NKCC2) isoforms of the co-transporter, we employed reverse transcription and the polymerase chain reaction (RT-PCR) to explore isoform diversity in inner ear tissues. Using NKCC1 and NKCC2 isoform-specific PCR primers based on mouse and human sequences, only transcripts for NKCC1 were detected in the gerbil inner ear. The presence of abundant NKCC1 in the basolateral plasmalemma of strial marginal and vestibular dark cells confirms conclusions drawn from pharmacological and physiological data. The co-expression of NKCC1 and Na,K-ATPase in highly specialized subpopulations of cochlear and vestibular fibrocytes provides further evidence for their role in recycling K+ leaked or effluxed through hair cells into perilymph back to endolymph, as postulated in current models of inner ear ion homeostasis.

Animals↗