Biomedical subjects

H Rask-Andersen

Publications and source records attributed to H Rask-Andersen.

At least 19 recordsLinked to original sources

PubMed2005

Smooth muscle in the annulus fibrosus of the tympanic membrane in bats, rodents, insectivores, and humans.

The annulus fibrosus and its attachment to the bony tympanic ring were studied in a series of mammals. In the pallid bat, Antrozous pallidus, there is an extensive plexus of large interconnected blood sinuses in the part of the annulus that borders the tympanic bone. The spaces between the sinuses are packed with smooth muscle cells. Most of the cells have a predominately radial orientation; they extend from the bony tympanic sulcus to a dense collagenous matrix (apical zone) where radially oriented fibers of the pars tensa are confluent with the annulus. The muscles and vessels constitute a myovascular zone. A structurally similar myovascular zone is also present in the European hedgehog. In rodents, the annulus lacks the large interconnected blood sinuses but many small vessels are present. Smooth muscle is concentrated in the broad area of attachment of the annulus to the tympanic bone. In the gerbil, smooth muscle seems to be concentrated in the central part of the width of the annulus where it is attached to bone and radiates toward the tympanic membrane. In humans collections of radially oriented smooth muscle cells were found in several locations. The smooth muscle in all species studied appears to form a rim of contractile elements for the pars tensa. This arrangement suggests a role in controlling blood flow and/or creating and maintaining tension on the tympanic membrane.

Aged↗

PubMed2001

High resolution deletion analysis of constitutional DNA from neurofibromatosis type 2 (NF2) patients using microarray-CGH.

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder whose hallmark is bilateral vestibular schwannoma. It displays a pronounced clinical heterogeneity with mild to severe forms. The NF2 tumor suppressor (merlin/schwannomin) has been cloned and extensively analyzed for mutations in patients with different clinical variants of the disease. Correlation between the type of the NF2 gene mutation and the patient phenotype has been suggested to exist. However, several independent studies have shown that a fraction of NF2 patients with various phenotypes have constitutional deletions that partly or entirely remove one copy of the NF2 gene. The purpose of this study was to examine a 7 Mb interval in the vicinity of the NF2 gene in a large series of NF2 patients in order to determine the frequency and extent of deletions. A total of 116 NF2 patients were analyzed using high-resolution array-comparative genomic hybridization (CGH) on an array covering at least 90% of this region of 22q around the NF2 locus. Deletions, which remove one copy of the entire gene or are predicted to truncate the schwannomin protein, were detected in 8 severe, 10 moderate and 6 mild patients. This result does not support the correlation between the type of mutation affecting the NF2 gene and the disease phenotype. This work also demonstrates the general usefulness of the array-CGH methodology for rapid and comprehensive detection of small (down to 40 kb) heterozygous and/or homozygous deletions occurring in constitutional or tumor-derived DNA.

Adolescent↗

PubMed2001

Selective aspects of human pathology in high-tone hearing loss of the aging inner ear.

Accompanied with aging, the thresholds for high frequency sounds may elevate and result in a progressive hearing loss described as presbycusis. Based on correlations between audiometric measures of aged patients and histologic findings garnered from postmortem examinations, four types of presbycusis have been characterized: sensory-neural, neural, strial, and conductive [Schuknecht, H.F., Gacek, M.R., 1993. Ann. Otol. Rhinol. Laryngol. 102, 1--16]. Otopathologic changes to the inner ear as a direct function of age, however, remain controversial. The focus of this investigation involves the pathological impact on remaining sensory structures in patients having sensory--neural degeneration. The current study presents seven human temporal bones extracted from patients aged 53--67 years with high-tone hearing loss and with no known history of extraordinary environmental events involving head or noise trauma, acoustic overstimulation, or ototoxicity. In previously published findings of these specimens, all but one temporal bone failed to demonstrate a meaningful correlation between audiometric measurements and loss of functional hair cell populations with secondary retrograde degeneration of nerve fibers. Using the block surface method, electron microscopic micrographs demonstrate ultrastructural changes in the cuticular plate, stereocilia, pillar cells, stria vascularis, and the spiral ligament. In all pathological specimens, the greatest incidence of degeneration was seen at the cuticular plate. Conclusively, our findings present three implications in the aging human cochlea: firstly, audiometric measures that represent a high-tone hearing loss may take various forms with respect to ultrastructural patterns of degeneration and surviving structures; secondly, the incidence of lipofuscin and lysosome granules does not correlate with the degree of hearing loss and; thirdly, as shown only in guinea pigs [Anniko, M., 1988. Scanning Microsc. 2, 1035--1041], high-tone hearing loss can be associated with deformation of the cuticular plate.

Adult↗

PubMed2001

A 3-D model of membrane specializations between human auditory spiral ganglion cells.

A three-dimensional model of the cell membrane contact area was made between two large spiral ganglion cells (type 1 cells) from a cell cluster in a normal human cochlea. The freshly fixed cochlea had been removed during skull base surgery, processed, and sectioned for ultrastructural analysis. 400 consecutive serial thin sections were prepared from the apical portion where the nerve cell density is high and cell clusters are numerous. A cell cluster is defined as a conglomerate of two or more nerve cell bodies, surrounded by common Schwann cells. Direct physical contact between ganglion cell membranes (ephapse) was possible, in places where adjacent cells lacked a separating Schwann cell layer (gaps). One such gap was selected, and observed in 57 of 90 consecutive sections. Membrane specializations, observed in 36 sections, were found to be of principally three different types namely: (1) symmetrical, (2) asymmetrical, and (3) asymmetrical subplasmalemmal. The functional properties of these membrane specializations are still unknown. Asymmetrical densities were seen on one or other of the two cell membranes. A graphic model based on serial thin sections was made to illustrate the gap area. Superficially membrane specializations were seen to form small disk-like areas varying in size, the largest measuring 3 x 2 microm. It is speculated whether these unique formations between human spiral ganglion cells, which have not been observed in other species, may constitute interactive electrotonic or ephaptic transmission pathways. These may be in the low-frequency region and may increase plasticity and signal acuity related to the coding of speech.

Auditory Pathways↗

PubMed2001

In vitro growth of human endolymphatic sac cells: a transmission electron microscopic and immunohistochemical study in patients with vestibular schwannoma and Ménière's disease.

HYPOTHESIS: Human endolymphatic sac cells have been notoriously difficult to maintain in culture. It was hypothesized that an in vitro environment intended for growth of keratinocytes would also be suitable for human endolymph sac cells. BACKGROUND: Studies on cell physiology of human endolymphatic sac cells have been hampered by difficulties in maintaining them in culture. METHODS: Human endolymphatic sac cells were taken from 10 patients during translabyrinthine skull base surgery for vestibular schwannoma, one of whom also had Ménière's disease. Cell lines of proliferating epithelial cells were obtained after trypsinization and growth in a 3:1 mixture of Dulbecco's modified Eagle medium and Ham's F12 medium supplemented with 10% fetal calf serum. Fibroblast overgrowth was counteracted by the use of so-called cloning rings. During various stages, cells were investigated with transmission electron microscopy and/or immunohistochemistry. RESULTS: Proliferation took place after 2 to 3 days of primary cell culture. The cells were cytokeratin-positive and pleomorphic, and they had abundant polarized microvillus-like projections, numerous coated cytoplasmic pits and vesicles, and a well-developed rough endoplasmic reticulum. CONCLUSION: Cell lines of proliferating human endolymphatic sac cells can be produced with the technique described here and may be a valid tool in studies of human endolymph sac physiology.

Cell Movement↗

PubMed2000

Synapses on human spiral ganglion cells: a transmission electron microscopy and immunohistochemical study.

A transmission electron microscopy (TEM) study and synaptophysin immunoreactivity analysis of neurons in the human spiral ganglion was performed with particular emphasis on the demonstration of synapses. The study was based on surgical biopsy material obtained during transcochlear meningioma surgery. Vesiculated nerve endings of unmyelinated nerve fibers occurred frequently on the small ganglion cells at all levels. The nerve terminals exhibited abundant clear synaptic vesicles but also dense-core vesicles. Multisynaptic contact sites were also seen with fibers of the intraganglionic spiral bundle (IGSB). Complex associations of synapses could be demonstrated, including several synaptic terminals in conjunction with contact sites or an adherent type of junctions on large ganglion cells. These contact sites exhibited membrane densities which were symmetric or asymmetric, changed their polarity recurrently over their extension from one cell to the other and back and lacked clear synaptic vesicles. This suggests the existence of connections between efferents, belonging to the olivocochlear bundle, and both small and large ganglion cells. Thus, both the inner and outer hair cell system may be under the influence of efferent innervation in the human spiral ganglion. The morphology and course of synaptophysin-positive nerve fibers indicated that synaptic contacts within the spiral ganglion, as observed under the electron microscope, may be abundant. These results indicate that complex neural processing may occur at the level of the spiral ganglion in man.

Humans↗

PubMed2000

Structural/audiometric correlations in a human inner ear with noise-induced hearing loss.

A morphological analysis was performed on a human cochlea removed during skull base surgery. The patient experienced a noise-induced hearing loss following 30 years of mechanical exposure. The tissue was processed according to the block surface technique and the organ of Corti, osseous spiral lamina and spiral ganglion were analyzed at different levels. There was a circumscribed lesion approx. 10 mm from the round window extending to about 13 mm. At this site, the dominant pathological feature was the loss of outer hair cells that was comprehensive in the centermost area and partial in the peripheral region of the damage. The degradation of inner hair cells was less severe with signs of cell atrophy yet with limited loss. Outer pillar cells were often collapsed leading to deformation of the acoustic ridge. The Deiters cells were often present and physically interactive with remaining nerve fibers. In the reticular lamina, surgical manipulation and dissection resulted in tears which may be attributed to a reduction of intercellular strength between cells. In the damaged area, there was a 45% loss of myelinated nerve fibers measured at the osseous spiral lamina. Pathological changes could not be observed in the spiral ganglion with certainty although the type II cells innervating the outer hair cells were often difficult to discern.

Audiometry↗

PubMed2000

Ultrastructural analysis of 20 intraosseous endolymphatic sacs from patients with cerebello-pontine angle tumours. A surgically obtained control material for histopathological studies.

OBJECTIVE: The purpose of this work was to collect a surgically obtained, freshly fixed material of the human intraosseous endolymphatic sac. This biopsy material was used to describe the normal ultrastructure as well as to serve as a control material for histopathological studies on Ménière's disease in particular. METHOD: The specimens, obtained during surgery for cerebello-pontine angle tumours, were fixed by immersion and then prepared by routine methods for transmission electron microscopy. The ultrastructural analysis was focused on intraluminal content, epithelial cell layer, subepithelial space, and morphological signs of immunological activity. The ultrastructure was analysed in relation to inner ear sensory function, tumour diagnosis, and patient's age and sex. RESULTS: As it was possible to obtain numerous specimens with an intact bony shell, the intraluminal substance could be analysed. Two separate epithelial cell types are described: one less abundant, often lighter and mitochondria-rich cell type; the other, often darker, epithelial cell with fever mitochondrias. Some of the latter cell types showed signs of active secretion. The subepithelial space was characterized by loose connective tissue adjacent to the epithelial lining, being more dense toward the bone. Elastic fibres were seen surrounding the entire endolymphatic sac. Macrophages in the intraluminal space and lymphocytes in the epithelial and subepithelial layers are described. No distinct morphology correlating to inner ear sensory function, tumour diagnosis, or patient's age and sex was revealed. CONCLUSIONS: This study confirms previously described, extensive variations in form and structure of the human endolymphatic sac. Various factors, such as surgical trauma, previous treatment, and processing method, can affect the ultrastructure and must be taken into consideration. The specimens described in this work appear to constitute a good control material for histopathological study of the human endolymphatic sac. It is still necessary to obtain large control materials such as this, as surgical specimens from patients with Ménière's disease are uncommon.

Adult↗

PubMed2000

Embryonic and postnatal accumulation of homogeneous substance in the endolymphatic sac in the guinea pig.

OBJECTIVE: The endolymphatic sac (ES) of vertebrates contains varying amounts of a homogeneous substance (HS) that stains deeply with basic aniline dyes. Histochemically, HS is characterized as a carbohydrate-protein complex, being both neutral and acidic in nature. In the present study, deposition of HS in the ES was studied in the guinea pig from the 3rd week of gestation to 104 weeks postnatally in order to find out if HS accumulates with age, at which point during embryonic development this substance appears, if its presence is correlated to the sense of hearing and if the amount of substance in the left versus right ear of one and the same animal is correlated to any degree. METHODS: Sixty-nine endolymphatic sacs were evaluated in 38 guinea pigs. The ES specimens were sectioned for light and transmission electron microscopy and the amount of HS filling was categorized in four groups: none, low, medium and a high level of substance. RESULTS: The substance was not discerned until after 7 weeks of gestation, when it filled only a minor part of the distal ES lumen. At 9 weeks gestation the nature of the substance altered, becoming homogeneous, as visualized by osmium-toluidine blue staining and approximately filling the distal half of the luminal space. In the postnatal period, 65% of ES specimens were filled with HS to the intermediate or proximal ES, whereas only 6.5% of the ES specimens were devoid of the substance. The extent of filling of the ES in the prenatal temporal bones was significantly less than postnatally (P < 0.0001, chi2-test). The extent of postnatal filling was not correlated with age. Left and right ears were closely correlated in one and the same animal. Phagocytic cells were often found at the border between clear endolymph and stainable substance. CONCLUSION: The appearance of HS seemed to coincide temporally with the onset of hearing during the prenatal period indicating that it could play a part in normal inner ear functioning in the guinea pig. The close correlation regarding the level of the HS in the left and right ear, both pre- and postnatally could reflect a general symmetry in endolymph pressure-volume conditions within the inner ear fluid systems, as well as in the environmental hydrostatic pressure in the posterior cranial fossa.

Animals↗

PubMed1999

Middle ear mucosa changes following exposure to Pseudomonas aeruginosa exotoxin A.

Pseudomonas aeruginosa exotoxin A (1 microgram/20 microliters) was instilled into the middle ear cavity in the rat. Morphological changes of the mucosa were analyzed after various intervals using light (LM) and transmission electron microscopy (TEM). An inflammatory cell reaction was seen in which there was a predominance of polymorphonuclear leukocytes (PMNs) and mononuclear cells that were mostly lymphocytes and monocytes/macrophages. Epithelial cells often showed signs of metaplasia and hyperplasia, followed by degradation through necrosis and/or apoptosis, resulting in denudation of the submucosal layer. A characteristic feature was the physical interaction between intraepithelial lymphocytes and epithelial cells. Lymphocytes adhering to the cell coat of epithelial cells showed signs of directed secretion that seemed to end in necrosis or apoptosis of the target cell. These changes occurred simultaneously with phagocytosis of cells and cell debris by PMNs and macrophages. Ultrastructural analysis suggested that intraepithelial, lymphocyte-mediated cytolysis and apoptosis may be important events in degradation of the epithelium following exposure to Pseudomonas sp. exotoxin. These findings indicate that denuding of the lamina propria may facilitate the penetration of toxin into the labyrinth, thus explaining subsequent inner ear damage.

ADP Ribose Transferases↗

PubMed1999

Morphological changes of the endolymphatic sac induced by microinjection of artificial endolymph into the cochlea.

Morphological changes of the endolymphatic sac were analyzed in guinea pigs following microinjection of artificial endolymph into the cochlea or withdrawal of a quantity of native endolymph. Injections were performed into the second turn of scala media with a micro-pump at a rate of 60-100 nl/min, lasting for a period of 4, 7. 5, 15 or 18 min. In withdrawal experiments, endolymph was aspirated from the second cochlear turn over a period of 8 min. For each procedure the contralateral (non-treated) ear served as a histological control. Following artificial endolymph injections of 7. 5 min or more there was an almost total absence of the normal intraluminal homogeneous substance (HS) on the injected side. Our observations suggest that the disappearance of the HS occurs by both enzymatic and macrophagic activity. After endolymphatic withdrawals the ES was found to contain increased amounts of HS. The results could suggest that the volume of fluid in the ES, and hence the volume of the entire membranous labyrinth, may be regulated by a dynamic relationship between active secretion and enzymatic degradation of a lumen-expanding substance that is intimately related to the intraluminal macrophages. The exact mechanism governing these regulatory systems, and their relationship to ion and water movements across the epithelium of the sac, remain to be elucidated.

Animals↗

PubMed1999

On a novel type of neuron with proposed mechanoreceptor function in the human round window membrane--an immunohistochemical study.

An immunohistochemical study was performed on surgically obtained human fresh cochlear tissue, using synaptophysin antibodies. After immediate aldehyde fixation and decalcification in Na-EDTA serial cryosections were made of the cochlea including the round window membrane (RWM). Apart from highly specific immunostaining of spiral ganglion cells and unmyelinated nerve fibers an immunoreactive neuroreceptor could be demonstrated at the postero-medial insertion of the RWM. The perikaryon showed intense synaptophysin immunoreativity with a distal process projecting into the fibrous stroma of the RWM displaying structural specializations suggestive of a mechanoreceptor function. It is speculated whether the neuroreceptor may be involved in the proprioception and/or mechanoreception of tensile forces generated within the lamina propria during displacement of the yielding RWM in the bony labyrinth. Such a function could be important for the regulation of perilymph pressure.

Basilar Membrane↗

PubMed1997

Quantitative evaluation of cochlear neurons and computer-aided three-dimensional reconstruction of spiral ganglion cells in humans with a peripheral loss of nerve fibres.

Quantitative data on human cochlear neuronal elements were collected from various regions in five patients with high-tone hearing loss due to presbycusis and in two patients with normal hearing. The number of nerve fibers was assessed in the spiral lamina and in the inner acoustic meatus together with counts of spiral ganglion cells. The results show that the number of neurons decreased peripherally, i.e., with increasing distance from the central nervous system in patients with high-tone hearing loss due to presbycusis. In two patients with normal hearing no significant difference in the number of neurons was found in the lamina spiralis as compared to the inner acoustic canal. Computer-aided 3-dimensional reconstruction of the human spiral ganglion displayed large bipolar neurons (type I cells), but also large ganglion cells with one missing axon. The results may indicate that a slow retrograde degeneration occurs from the periphery towards the spiral ganglion in presbycusis. Transmission electron microscopy analysis of freshly fixed human spiral ganglions displayed interneural connections. It is speculated whether a trophic supply from other neurons at the level of the spiral ganglion can prevent or delay further degeneration of the central axon.

Aging↗

PubMed1997

Nerve fibre interaction with large ganglion cells in the human spiral ganglion. A TEM study.

A TEM study was performed on freshly fixed human spiral ganglions (HSG) biopsied during skull base surgery. Well preserved tissue specimens were obtained for ultrastructural analysis. The investigation revealed that nerve fibres frequently form contacts with the large ganglion cells (type I cells). In the areas of contact, membrane specializations occurred, consisting of symmetric or asymmetric densities often alternating from one cell to the other with a reduced intercellular distance (approximately 10 nm). High power TEM showed the intercellular cleft to contain an extra dense line resulting in a pentalaminar structure. The dense line appeared on the side of the membrane protein concentration. Protein densities jutted into the cytoplasm along the intracellular face spreading into a diffuse cytoplasmic web physically related to accumulating mitochondria. This indicated a concentration of oxygen-dependent metabolic activity in these regions. It is believed that the nerve junctions are involved in electric transmission between type I ganglion cells. The neural junctions were morphologically different from synaptic contacts between small human ganglion cells (type II cells) and nerve fibres which have been suspected of sharing the olivocochlear bundle as their origin.

Axons↗

PubMed1997

"Endolymphatic sacitis" in a case of active Menière's disease. An ultrastructural histopathologic investigation.

An ultrastructural analysis of an entire intraosseous endolymphatic sac (ES) from a patient with active, well-documented Menière's disease was performed for the first time. The results were compared with those obtained from ES biopsy material from patients with acoustic neuromas. The ES was small in size and showed signs of focal inflammation with intraepithelial invasion by mononuclear cells. At these places the normal fine structure, including the vascular anatomy, was altered. The possible relationship between these changes and Meniere's disease is discussed.

Endolymphatic Sac↗

PubMed1997

Neural interaction in the human spiral ganglion: a TEM study.

A TEM study was performed on freshly fixed human spiral ganglions (HSG) collected during skull base surgery. This technique gives well preserved tissue for ultrastructural analysis. Unlike spiral ganglion cells in mature animals so far studied, most HSG cells lack a myelin coat, but are surrounded by a thin rim of Schwann cell (SC) cytoplasm. In the region of maximal innervation density (upper basal and middle turn), HSG cells were frequently ensheathed by the same Schwann cell, forming a "unit-like" structure. In this region the cells often showed signs of physical interaction where the SCs were frequently incompletely developed ("gaps") so that the cell membranes of adjacent ganglion cells (sometimes as many as four in one section plane) were in direct apposition. In one thin section as many as 20 of 100 ganglion cells were found to face the cell membrane, at any point, of an adjacent cell. At these "gaps" in the SC, complexes of cell membrane specializations occurred between individual HSG cells. The same nerve junctions were also found between unmyelinated nerve fibres and the body of large ganglion cells. Our findings may challenge the view that afferent information in the acoustic nerve is conveyed uninterrupted to the CNS at the level of the spiral ganglion.

Cell Membrane↗

PubMed1997

Cochlear changes following destruction of semicircular canal in healthy and previously toxin-exposed rats. An electrophysiological and morphological investigation.

One group of Sprague-Dawley rats (group A, n = 6) was treated by instilling Pseudomonas aeruginosa exotoxin A (PaExoA), and another (group B, n = 6) treated similarly with Haemophilus influenzae type b endotoxin (HiBEndo). In group A a 20 dB hearing loss was observed, predominantly in the high-frequency region, which was reversible within 1 month. In group B no significant hearing impairment was noted. Between 1 and 6 months later, the lateral and posterior semicircular canals (SCCs) were ablated unilaterally. Control rats (group C, n = 8) were subjected to ablation only. All rats were cochleotomized contralaterally prior to labyrinthine surgery. Frequency-specific evoked potential testing at 2-31.5 kHz tone bursts was performed before and directly after surgery, 6, 24 and 48 hours and 1, 4 and 16 weeks postoperatively. After surgery in 18 rats, thresholds rose immediately, predominantly at 2, 4 and 6 kHz, followed by varying degrees of recovery. Greatest immediate postoperative hearing loss was observed in group A; no rat recovered completely and two rats showed severe permanent threshold elevation. All group B rats recovered completely, except one showing moderate threshold impairment. No permanent hearing loss was observed in group C. This study shows that destruction of SCCs in rats does not necessarily cause permanent hearing loss, even if the fluid spaces are not sealed off. However, previous exposure of the middle ear to PaExoA (but not HiBEndo) renders the cochlea more vulnerable and can result in persistent hearing loss.

Animals↗

PubMed1997

Auditory epidermal cell migration. VII. Antigen expression of proliferating cell nuclear antigens, PCNA and Ki-67 in human tympanic membrane and external auditory canal.

A location of proliferating cells was investigated in eight human normal tympanic membranes (TMs) and external auditory canals (EACs) by an immunohistochemical method using two different types of antibodies for nuclear antigens in proliferating cells: anti-PCNA monoclonal antibody, and anti-Ki-67 polyclonal antibody. Four specimens prepared for cryostat sections were immunostained by both antibodies. Another four were fixed in 4% formaldehyde solution, embedded in paraffin wax and were reacted only with anti-PCNA antibodies. The expression pattern of Ki-67 was basically the same as of PCNA. In the pars tensa (PT), immunoreactivities were expressed in the nuclei of basal layer cells and cells just overlying the basal layer of epidermis both in the handle of the malleus (HM) and annular regions. In the intermediate region of the PT, no immunoreactivity was found basically, apart from a few labelled cells observed in the upper-third of the superior quadrant. In the pars flaccida (PF) and in both the osseous and cartilaginous regions of the EAC, positive cells were also situated in the basal layer and the deeper aspect of the suprabasal layers without any specific distributing pattern. It was certified that the generation centre of epidermal cells (keratinocytes) in the PT was located in both the HM and annular regions, and that stem cells in the PF and the EAC were uniformly scattered in the basal layer and the deeper aspect of the spinous layer. According to these findings, the migratory patterns of auditory epidermal cells in the human TM and EAC were discussed.

Antibodies, Monoclonal↗