The inner ear and the in vitro system

Summary The embryologic labyrinthine development of the CBA/CBA mouse occurs parallell in vivo and in vitro. Regarding post partum inner ears, either as cultured otocysts passing a corresponding time in vitro or inner ear explants of newborn/mature animals, the extracorporal system becomes unable to maintain specialized hair cell structures for more than a few days. The sensory cells themselves, however, survive for considerably longer time. Vestibular hair cells show sensory hair fusion. Cochlear hair cells loose their surface structures but the sensory hair rootlets penetrating into the cuticle are preserved. Post partum inner ears from the guinea pig reacted in a similar way in vitro as did labyrinths from the CBA/CBA mouse.Supported by grants from Karolinska Institutet, The Swedish Medical Research Council (grant no 12X-720) and The Swedish Society of Medical Sciences     

Alcohol and ultrastructural changes in the developing inner ear. An in vitro study

Inner ear explants from the CBA/CBA mouse were used in an organ culture system. The explants were cultured from the 16th gestational day until one day post partum. They were exposed to 1.5% or 3% ethanol in organ culture medium in order to determine any possible toxic effects upon the differentiating sensory structures of the sensory epithelium of the inner ear, that could be correlated to fetal alcohol syndrome. The higher concentration of ethanol caused a general and possibly unspecific destruction of the sensory epithelium, while the lower concentration caused characteristic changes including intracellular edema or vacuolization, especially confined to hair cells. Pathologic changes seemed dose-related but not time-related.     

Experimental immune system of the inner ear

The observation that certain clinical cases of sensorineural hearing loss could favorably respond to immunosuppressive therapy in addition to experimental studies that support the presence of an inner ear immune system have led to the suggestion that a number of inner ear disorders previously considered to be idiopathic may in fact have an immunological basis. The experimental evidence that establishes the operation of a distinct inner ear immune system is presented.     

The new classification system for inner ear malformations: the INCAV system

Conclusions: The proposed INCAV system standardizes reporting of inner ear malformations; gives adequate information about the structures of inner ear; defines the ears which could not be classified before; and helps in the selection of the ear as the cochlear implant candidate. Also it is easy-to-use for radiologists, and useful to the referring otolaryngologists.

Objective: This study was conducted to explore a more specific, definitive classification system which was based on radiological criteria for inner ear malformations.

Method: This study found 43 patients who had inner ear malformations, magnetic resonance (MR), and computed tomography (CT) imaging, together with the retrospective evaluation of the medical records between August 2010 and February 2015. It analyzed inner ear structures by dividing five sub-groups and each sub-group was given a letter: internal acoustic canal (I), cochlear nerve (N), cochlea (C), vestibular aqueduct (A) and vestibule (V). Based on their malformations, these anatomical structures have been assigned grades and have been classified by using increasing numbers which were dependent to increasing order of severity of the malformation.

Results: Among these 43 patients, there were six normal (I₀N₀C₀A₀V₀) and 80 inner ear malformations. All of the ears were defined successfully by the INCAV system.     

Connection between the inner ear and the lymphatic system

OBJECTIVE: The aim of this study was to identify the lymphatic drainage of the inner ear in guinea pigs. STUDY DESIGN: Prospective study. METHODS: The prospective study was performed in guinea pigs by injection of keyhole limpet hemocyanin (KLH) into either the right-side scala tympani or the middle ear cavity. The left side was not injected and served as a control. Fifteen minutes after injection, the animals were killed by intracardiac perfusion with paraformaldehyde and tissue specimens (right and left temporal bones, cervical lymph nodes, and the spleen) were collected. The presence of KLH in each specimen was determined by immunohistochemical assay of frozen sections using polyclonal mouse anti-KLH antibodies. RESULTS: After injection into the middle ear, labeled cells were identified in the parotid, superficial ventral, mandibular, and deep cranial cervical lymph nodes. However, after inner ear injections KLH was present in only the parotid and superficial ventral cervical nodes. The spleen contained KLH-positive cells following injection into either the middle or inner ear, but not all animals contained labeled spleen cells. CONCLUSIONS: The inner ear has a connection to the lymphatic drainage system. Because fewer lymph nodes contained labeled cells after inner ear injection than after middle ear injection, it is concluded that the inner ear does not simply drain to the middle ear and subsequently to the lymph nodes but seems likely to have its own connections.     

Embryogenesis of the inner ear. II. The late differentiation of the mammalian crista ampullaris in vivo and in vitro

The embryonic development of the crista ampullaris of the CBA/CBA mouse was followed both in organ culture of explanted inner ears of the 16th gestational day and in vivo from the 16th gestational day until the 21st day, an age corresponding to birth. Cytodifferentiation of the sensory epithelium of the crista ampullaris occurs during this period. At partus, there is a rather mature crista with well developed hair cells and 1-2 layers of supporting cells. Innervation and differentiation into type I and type II hair cells have started prior to partus but occur mainly post partum. The in vitro development followed that of the in vivo but with a slight delay, especially concerning the later stages of the in vitro development. At the time corresponding to partus, differentiation of hair cells is almost identical in the two groups but innervation is delayed in the in vitro group of inner ears. Because of the very high reproducibility/stability in vitro and morphologic maturation of both hair cells and gross structure of the crista ampullaris, organ culture of the 16th gestational day inner ear explant is a suitable model in the study of the late embryonic development under normal and pathological conditions.     

Junctional complexes of the in vitro developed inner ear. A freeze fracture study

The freeze fracture technique was used to study intercellular junctions of inner ear anlages developed in vitro. The 16th gestational day inner ear from the CBA/CBA mouse was cultured for 5 days whereafter the specimens were analyzed. Inner ears developed in vivo were used as controls. A considerable variation in the maturation of the tight junctional complexes occurred in both the vestibular and cochlear parts of the labyrinth. The sequential maturation of tight junctions and gap junctions showed the same structural features in the in vivo and the in vitro developed inner ears, although it seemed that the in vivo developed inner ears showed a slightly more overall mature morphology of tight junctions.     

Immune-mediated inner ear disease.

Recent clinical studies, experimental research, and various testing techniques in otoimmunology have resulted in presentation of the synonymous terms autoimmune sensorineural hearing loss, autoimmune inner ear disease, immune-mediated sensorineural hearing loss, and immune-mediated inner ear disease or disorder. The development of this terminology and the clinical presentation of this disease as well as whether it is really a distinct clinical entity are discussed. Laboratory tests for immune-mediated inner ear disease are presented along with a discussion of progress being made in the growing field of otoimmunology.     

The inner ear fluids in man

The microchemical analysis of human inner ear fluid has not only advanced our knowledge of inner ear function in normal and pathological states, but also has added another dimension to our diagnostic armamentarium in inner ear disease. The purpose of this thesis is

• 1 To review and evaluate all pertinent literature concerning the chemistry of human inner ear fluids.
• 2 To determine what percentage of inner ear fluids can be collected without contamination by hemolyzed cells (hemoglobin) or erythrocytes.
• 3 To study the glucose concentrations in human inner ear fluid in various pathological states.
• 4 To present the data from uncontaminated endolymph samples in Ménière's disease.
• 5 To study the correlation between the clinical picture of acoustic neurinoma and the results of inner ear fluid analysis.
• 6 To evaluate the present status of diagnostic labyrinthotomy (labyrinthine tap).

     

Non-insulin-dependent diabetic microangiopathy in the inner ear.

Hearing loss has long been associated with diabetes mellitus. Microangiopathy, associated with thickening of the basement membranes of small vessels, has been implicated as a major source of multiple system organ disease. OBJECTIVE: This study was designed to evaluate changes in basement membrane thickness in the inner ear of laboratory animals suffering from non-insulin-dependent diabetes mellitus (NIDDM) with, and without, exposure to moderate intensity noise exposure in an attempt to extrapolate the same disease process in humans. DESIGN: Spontaneously hypertensive-corpulent non-insulin-dependent rats (SHR/N-cp) were selected as a genetic model for the above study. Both lean and obese rats were used in this study. A genetically similar control group of animals (LA/N-cp) were used as controls. These animals express both the lean and obese phenotypes, but they lack the NIDDM gene. Forty-eight animals in each group were sacrificed at the end of the study. The cochleas were dissected and fixed. The basement membrane of the stria vascularis was examined using transmission electron microscopy. SETTING: This study was a laboratory-based, standard animal study. MAIN OUTCOME: This study was designed to show microangiography of the inner ear as related to NIDDM with, and without, obesity and noise exposure. RESULTS/CONCLUSIONS: NIDDM alone does not cause statistically significant basement membrane thickening; however, NIDDM in combination with obesity and/or noise exposure did show significant thickening and the combination of all three showed the greatest thickening. NIDDM appeared to be the greatest contributing factor.     

The fine structure of lipofuscin in the human inner ear.

Lipofuscin inclusions in the human membranous labyrinth were studied by electron microscopy. Lipofuscin is morphologically an irregularly shaped, membrane-bound inclusion consisting of an electron-dense structure. The most common component was a fine, granular, osmiophilic substance which was always associated with a homogenous, spherical structure resembling a lipid droplet. The combination of these two components was frequently observed in the human inner ear. Distended inclusions containing lipofuscin components were also observed within the supporting cells, saccular, utricular and ampullar wall, the epithelial cells of the transitional zone and in the dark cells. Lipofuscin is closely associated with lysosome and is known to accumulate in the tissue as a result of aging. The high lysosomal activity possibly may result in lipofuscin formation in the human inner ears. Also some other unknown metabolic conditions may provide the deposits of lipofuscin.     

Normal anatomy of the inner ear.

The three parts of the inner ear have been reviewed: the membranous (endolymph containing) labyrinth surrounded by the osseous (perilymph containing) labyrinth, and the otic capsule of bone that encases the osseous labyrinth. This is a brief survey of the normal anatomy, but one must always remember that the hallmark of the temporal bone is variation.