Helge Rask-Andersen

The endolymphatic sac in a mouse mutant with cochleo-saccular degeneration: Electrophysiological and ultrastructural correlations

The response of the endolymphatic sac to a disturbance in endolymph homeostasis was investigated by examining the sac in a mouse mutant, viable dominant spotting, which is known to exhibit primary strial dysfunction and cochleo-saccular degeneration. The function of the vascular stria was assessed by measuring the endocochlear potential and the sacs were then studied by light and transmission electron microscopy. The endolymphatic sac was found to be morphologically abnormal in these mutants, the main abnormality being the presence of granular epithelial cells, which showed clear histological signs of secretory activity. A stainable precipitate, believed to be secreted by the granular cells, was observed in the lumen of the endolymphatic sac in the mutants. The findings strengthen the view that the sac is involved in the regulation of endolymph volume and pressure.

THE FUNCTION OF THE ENDOLYMPHATIC DUCT—AN EXPERIMENTAL STUDY USING IONIC LANTHANUM AS A TRACER: A PRELIMINARY REPORT*

Guild’s original concept of endolymph flowing from the cochlea through the reunion duct into the saccule, thence out to the endolymphatic duct and sac for reabsorption, is still supported by several recent investigation^.-^ The mechanisms underlying this “longitudinal” flow of endolymph towards the sac and the transport across the epithelial membrane are still obscure. We focused our interest on the narrow epithelial pathway connecting the endolymphatic sac with the rest of the membranous labyrinth, the endolymphatic duct. It is a small tubule lined by a single-layered epithelium where individual cells appear to be sealed together by fairly shallow intercellular junctions. The epithelium is encompassed by a wide zone of loose vascular tissue incorporating a lymphatic vascular network. No details of the ultrastructural anatomy of the endolymphatic duct will be given here, as they are already on record.’ In this investigation, we used ionic lanthanum as a tracer in order to provide morphological evidence of an intercellular (or paracellular) fluid pathway between cells lining the endolymphatic duct in the guinea pig. The tracer was introduced into the scala media of the cochlea in small, controlled amounts. After various intervals, the endolymphatic duct and sac were investigated ultrastructurally in order to trace the lanthanum.

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.

How to predict cochlear length before cochlear implantation surgery.

Abstract Conclusions: The basal turn diameter of the human cochlea predicts the outer wall length of the basal and two first turns relatively well but there was less correlation for the total cochlear length. The linear regression graph defines the length of the basal turn within an error of ± 1 mm and could be used clinically to distinguish small and large cochleae. Objective: The human cochlea varies in size. The preoperative assessment of cochlear length can be crucial for non-traumatic electrode insertion and hearing preservation. In this study, we estimated the external cochlear wall length by assessing the basal turn diameter. Methods: A total of 51 non-selected, human inner ear moulds were analysed. A line was drawn from the midpoint of the round window through the cochlear mid-portion to the opposite side (A) and correlated to the cochlear turn lengths. Linear regression analyses were carried out. Results: Mean diameter A was 9.3 mm. The mean basal turn length was 22.8 mm, the two first turns were 35.1 mm and the total length was 41.2 mm. Linear regression analyses indicated a coefficient of determination (R2) of 0.74 for diameter A and the basal turn length, R2 = 0.70 for the two-turn length and R² = 0.39 for the total length.

Is the Human Round Window Really Round? An Anatomic Study With Surgical Implications

Hypothesis Human round window (RW) presents anatomic variations that may influence surgical approach. Background The true shape of the human RW has been divisive since its first description in 1772 by Antonio Scarpa. Introduction of novel surgical strategies in recent years have raised its significance. Here, the human RW size and shape variations were documented in microdissected human temporal bones. Methods An archival collection of human microdissected temporal bones was analyzed. RW rim could be delineated and photographed from the labyrinthine aspect and its topography assessed. Results Human RW is seldom round but ovoid or orthogonal, skewed, and nonplanar (saddlelike). Membrane is fan shaped or conical with an anteroinferior and a posterosuperior part. The mean longest diameter was 1.90 mm, and the smallest one is 1.54 mm. The mean diameter from the crista fenestra was 1.31 mm. The mean area of the RW was 2.08 mm2, which varied between 0.99 and 3.20 mm2. The crista fenestrae of the anterior component form a “doorstep” that may limit the entry to the scala tympani from the RW niche. Conclusion The alternate anatomic features of the human RW may influence its surgical access and designs of implants aimed at targeting this region.

Localization of prostanoid receptors and cyclo-oxygenase enzymes in guinea pig and human cochlea

Endogenous production of prostaglandins has been demonstrated in the cochlea, but no information is available on the distribution of the cyclo-oxygenase (COX) enzymes, or prostanoid receptors in the cochlea. The purpose of the present study was to investigate the localization of the FP, EP(1) and EP(3) prostanoid receptors as well as the COX-1 and COX-2 enzymes in the cochlea of guinea pig and man. Cochleas were processed for immunohistochemistry using routine techniques. Appropriate controls comprised incubation with specific blocking peptides, or incubation without primary antibodies. Both in guinea pig and man the FP prostanoid receptor was abundantly distributed in the cochlea, e.g., in stria vascularis, the spiral ligament, spiral ganglion, and organ of Corti. The immunohistochemical staining of the EP(1) and EP(3) receptors in the same structures was significantly weaker and sometimes lacking altogether (e.g., EP(3) receptor in human cochlea). Weak, but mostly consistent immunostaining of the COX-1 enzyme was found in the cochlear structures. The COX-2 enzyme appeared to be lacking. The abundant distribution of the FP receptor in several important cochlear structures both in guinea pig and man suggests a physiological function for PGF(2alpha) in the cochlea. The COX-1 enzyme seems to be constitutively expressed in the cochlea in contrast to COX-2.

Membrane junctions between odontoblasts and associated cells

The relationship between odontoblasts and adjacent cell structures within the odontoblastic cell layer was analyzed by means of the freeze-fracturing technique. Two principal forms of interodontoblastic cell structures were found. The first was tubular or thread-like in appearance, having a general diameter around 0.1-1.0 micron. From morphological criteria these were believed to represent small, unmyelinated nerve fibers. The second type of cell structure found between odontoblasts was more irregular and heterogeneous in outline, and often lamellar or branched. These slender formations sometimes proved to constitute cellular projections from adjacent odontoblasts or neighboring, subodontoblastic fibroblasts. Both the nerve-like fibers and the irregular branched cells between the odontoblasts showed morphological contact areas with odontoblastic cell bodies. At these sites the intracellular distances were reduced, and characteristic gap junctional complexes occurred. Nerve ending specialization or membrane structures indicating the presence of chemical synapses on the odontoblastic cell surface were not observed.

On the anatomy of the 'hook' region of the human cochlea and how it relates to cochlear implantation.

Background: The optimal insertion route for an electrode array in hearing preservation cochlear implantation (CI) surgery is still tentative. Both cochleostomy (CO) and round window (RW) techniques are used today. In the present study we analyzed size variations and topographic anatomy of the ‘hook region of the human cochlea to better comprehend the Testo effects of various electric array insertion modes. Material and Methods: Size variations of the cochlear ‘hook region were assessed in 23 human, microdissected temporal bones by measuring the distances between the oval and round windows, also outlining the spiral ligament/spiral lamina. Influence of size variations on spiral ligament position and fundamentals for different surgical approaches were evaluated in a subset of ‘small and ‘large cochleae performing different types of CO. In addition, the relationship between the microdissected accessory canal housing the inferior cochlear vein and the RW was analyzed. Results: The lateral vestibular wall and the cochlear ‘hook displayed large anatomic variations that greatly influenced the size of the potential surgical area. Results showed that only very inferiorly located CO entered the scala tympani without causing trauma to the spiral ligament and spiral lamina. An inferior approach may challenge the inferior cochlear vein. Conclusion: Preoperative assessment of the distance between the round and oval windows may direct the surgeon before CI hearing-preservation surgery. CO techniques, especially in ‘small ears, may lead to frequent damage to the inner ear structures. In those cases with substantial residual hearing, CI surgery may be better performed through a RW approach. i 2014 S. Karger AG, Basel

Membrane junctions in the subodontoblastic region. A freeze-fracture study of the human dental pulp.

The morphology of the subodontoblastic region in the human dental pulp was analysed using the freeze-fracturing technique. Multiple areas of focal intercellular junctions were found between subodontoblastic fibroblasts (or Höhls cells). The connections were of the gap junction type. Similar junctions were observed between subodontoblastic cells and small-calibre (0.10-0.20 microns) fibres, presumably nerves. Tight junctions were not observed.

Network Organization of Interstitial Connective Tissue Cells in the Human Endolymphatic Duct

The human endolymphatic duct (ED) and sac of the inner ear have been suggested to control endolymph volume and pressure. However, the physiological mechanisms for these processes remain obscure. We investigated the organization of the periductal interstitial connective tissue cells and extracellular matrix (ECM) in four freshly fixed human EDs by transmission electron microscopy and by immunohistochemistry. The unique surgical material allowed a greatly improved structural and epitopic preservation of tissue. Periductal connective tissue cells formed frequent intercellular contacts and focally occurring electron-dense contacts to ECM structures, creating a complex tissue network. The connective tissue cells also formed contacts with the basal lamina of the ED epithelium and the bone matrix, connecting the ED with the surrounding bone of the vestibular aqueduct. The interstitial connective tissue cells were non-endothelial and non-smooth muscle fibroblastoid cells. We suggest that the ED tissue network forms a functional mechanical entity that takes part in the control of inner ear fluid pressure and endolymph resorption.