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Biomedical subjects

C G Wright

Publications and source records attributed to C G Wright.

106 records · Page 6Linked to original sources
PubMedDate not supplied

Cochlear innervation in the guinea pig. I. The inner spiral bundle region.

The organization of nerve fibers in the vicinity of the inner hair cells of the guinea pig cochlea was studied in silver-stained whole-mount specimens by light microscopy. In all turns of the organ of Corti the inner spiral bundle (ISB) was found to contain both short and long spiral fascicles coursing toward either the base or the apex. The ISB is largest and its organization is most complex in the upper basal and lower second turns. It becomes markedly reduced in size in the apical and lower basal turns. Many ISB fibers cross the tunnel of Corti to the outer hair cells. Surgical interruption of the efferent nerve supply in the brain stem resulted in degeneration of all ISB fibers. After elimination of the efferents it could be seen that the majority of afferent fibers end on the inner hair cells.

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Cochlear innervation in the guinea pig. II. The spiral tunnel bundle.

The organization of nerve fibers in the spiral tunnel bundle (STB) of the guinea pig organ of Corti has been studied by light and electron microscopy. In the basal turn STB fibers were found to run toward the base or apex in about equal numbers while in the upper turns they ran predominantly in an apical direction. Long spiral fascicles of 100 microns or more in length were abundant in the third and fourth turns, but were rarely seen in the lower turns. No synaptic contacts between tunnel bundle fibers could be found and no afferent nerve fibers were seen in the bundle. Furthermore, interruption of the efferent nerve supply resulted in complete degeneration of the STB. The tunnel bundle does not, therefore, appear to be a site of synaptic interaction between afferent and efferent neutral elements.

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Efferent nerve fibers associated with the outermost supporting cells of the organ of Corti in the guinea pig.

In whold-mount preparations of the organ of Corti nerve fibers are sometimes seen peripheral to the third-row outer hair cells where they appear to wander among the Hensen cells. These fibers were studied in the guinea pig by both light and electron microscopy. In the upper second, third and fourth cochlear turns nerve fibers were seen between and on the peripheral side of the third-row Deiters cells as well as in the floor of the outer tunnel space. They were not found in the intercellular spaces between the Hensen cells. These nerve fibers are continuous with the spiral efferent fibers beneath the outer hair cells. Also their ultrastructural and histochemical characteristics indicate that they are efferent neural elements. This identification was confirmed by the finding that they degenerate following interruption of the olivo-cochlear bundle in the brain stem.

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Neural damage in the guinea pig cochlea after noise exposure. A light microscopic study.

Neural damage produced by exposure to 8 kHz octave-band noise was studied by light microscopy in guinea pigs. Abnormal nerve endings were found beneath both inner and outer hair cells within 24 hours after exposure at either 118 or 120 dB SPL. In areas where the organ of Corti was destroyed degeneration of myelinated nerve fibers was seen immediately after 24-hour exposures. Nerve degeneration secondary to hair cell loss was observed. However, degeneration of myelinated fibers occurred in some cases without significant hair cell loss. At survival times as long as two months nerve fibers coursing near capillaries were still present in extensively damaged areas. In three animals nerve fibers which had apparently regenerated into regions where the sensory epithelium was destroyed were found distal to the habenula perforata. Evdence of regenerative activity was also noted in the osseous spiral lamina.

Acoustic Stimulation↗
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Horseradish peroxidase acute ototoxicity and the uptake and movement of the peroxidase in the auditory system of the guinea pig.

When guinea pig cochlea was perfused in vivo with a solution of 1% horseradish peroxidase (HRP) in artificial perilymph, the enzyme was found in the basilar membrane, spiral limbus, some outer and inner hair cells and some supporting cells and it was gradually cleared away with time. Acute signs of cell damage included swelling, vacuolization and diffuse labeling of some hair cells, but stereocilia remained normal in configuration. Albino melanocytes of the spiral ligament were also damaged, and vacuolization of Reissner's membrane occurred after 10% HRP. Both concentrations caused a gradual decline in CM, showing that HRP is acutely ototoxic but its mode of action is unknown. No retrograde transport of HRP to spiral ganglion cells or to brain stem neurons occurred, but some brain stem neurons took up HRP from the neuropil following diffusion from the cochlea.

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Observations of otoconial membranes from human infants.

The microdissection technique was used to study otoconial membrane from 30 human infants ranging from newborn to 2 years of age. Both saccular and utricular membranes were quite variable in overall shape. During the neonatal period, the gelatinous layer of the otoconial membrane appears to thicken and become less adherent to the macular surface than in the fetal period. In many infants older than 6 weeks, otoconial membranes were found at autopsy to be completely dislodged from the maculae, with abnormally large saccular otoconia present in four specimens. Fourteen of the infants studied died of sudden infant death syndrome and 16 died of other causes. The incidence of detached otoconial membranes was approximately the same in both groups. Although the majority of these membranes were apparently dislodged post mortem, the present findings suggest that otoconial membranes are susceptible to pathological alteration due to disease or head trauma.

Acoustic Maculae↗
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Defects of the otoconial membranes in normal guinea pigs.

Otoconial membranes from a large number of normal albino and pigmented guinea pigs were examined by light microscopy. In more than 20% of the animals, microdissection revealed that the crystalline layer of the otoconial membrane was incomplete, leaving large areas of the underlying gelatinous layer uncovered by crystals. These defects were bilateral, more or less symmetrical, and invariably more extensive in the saccule than in the utricle. In two animals, huge single conglomerates of crystals were found on both the saccular and utricular maculae. None of the animals displayed abnormal behavior or posture and no obvious cause for the otoconial defects was found. The presence of a hereditary congenital condition is postulated. The high incidence of otoconial defects in guinea pigs makes them poorly suited for most investigations of experimentally induced pathology. Therefore, previous reports of otoconial pathology in guinea pigs should be viewed in the light of these findings.

Acoustic Maculae↗
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Streptomycin-induced defects of the otoconial membrane.

Damage to the neuro-epithelium caused by the vestibulotoxic drugs has been well described in previous reports; however, little is known about the effect of such drugs on the otoconia. In this investigation, streptomycin sulfate was found to create a circumscribed defect in the crystalline layer of the otoconial membrane in the utricle of the guinea pig. The defect was secondary to a sharply outlined lesion of the neuroepithelium which corresponded in size and location to the otoconial defect. Many of the otoconia along the margin of the defect showed signs of degeneration and appeared similar to those observed in the saccule of man during aging. In advanced stages of decay, the otoconia were reduced to hollow shells consisting of longitudinal interconnecting strands. All the epithelial lesions occurred with remarkable consistency in the same region of the macula utriculi at the posterior end of the striola.

Acoustic Maculae↗
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SEM observations on development of human otoconia during the first trimester of gestation.

The early development of human otoconial membranes was studied by scanning electron microscopy and X-ray microanalysis; 87 specimens, ranging from 7 to 12 weeks gestational age were examined. A few otoconia, which contained calcium, were present in the utricle by the end of the seventh week. By 8 weeks, both the saccule and utricle contained otoconia and differentiation of the macular neuroepithelia was well underway. At all stages, the utricular otoconia appeared more mature and were more varied in size and shape than saccular otoconia. In 12-week specimens, the maculae were covered by otoconial membranes with clearly defined crystalline and gelatinous layers. Near the end of the first trimester, newly-formed otoconia were present on the inferior utricular wall. X-ray analysis showed that a marked increase in otoconial calcium content occurs during the period from 7 to 12 weeks gestational age.

Acoustic Maculae↗
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Abnormal otoconia and calcification in the labyrinths of deaf Dalmatian dogs.

Abnormal mineral deposits from the membranous labyrinths of deaf Dalmatian puppies were examined microscopically. Most such deposits were located on the saccular otoconial membrane and were associated with collapse of the saccule and of Reissner's membrane. In both ears of one pup, crystals resembling otoconia were found on the surface of the stria vascularis. In two others, grossly abnormal crystals were seen on the utricular otoconial membrane, and in one of these crystals were also attached to the cupula of the left horizontal canal. In four animals the tectorial membrane was calcified. Most deposits consisted of apatite spherulites, but large multiple crystals (probably of calcite) were occasionally present. Some of the abnormal mineral deposits in the Dalmatian closely resemble those found in man, and they may originate in the same way.

Animals↗
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Pigmented epithelial cells of the membranous saccular wall of the chinchilla.

The posterior-superior portion of the membranous wall of the chinchilla saccule is lined by pigmented epithelial cells which contain golden brown granules having three components (lipid droplets, granular matrix, and dense globules). Histochemical and electronmicroscopic studies indicate that the dense component is a form of melanin. The pigmented cells show morphological features suggestive of fluid transport function; they are also involved in decalcification and phagocytosis of otoconial crystals. These findings provide evidence that the saccular wall epithelium plays an active role in regulating endolymph composition and in clearance of debris from the endolymphatic space.

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Experimental cholesteatoma. Epidermal ingrowth through tympanic membrane following middle ear application of propylene glycol.

This study was designed to investigate morphological changes in the tympanic membrane (TM) associated with cholesteatoma formation in experimental animals following application of propylene glycol to the middle ear. A 50% solution of propylene glycol was applied bilaterally to the middle ear cavities of 30 young-adult chinchillas. The animals were sacrificed for light and electron microscopic study at intervals of 2 days to 6 weeks after a single application of 0.2 ml of the propylene glycol solution. At 2 days there was complete destruction of the epidermal and mucosal layers of the TM. The denuded lateral surface rapidly became re-epithelialized by hyperplastic epidermal cells and by 2-3 weeks, keratinizing epidermis penetrated damaged areas of the fibrous layer of the lamina propria to reach the medial surface of the TM. These epidermal cells proliferated in the middle ear cavity, forming cholesteatomas. Our observations indicate that invasion of the intact, but structurally altered, tympanic membrane by hyperplastic epidermis is a primary mechanism of cholesteatoma formation in the animal model.

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Pigmented cells of the stria vascularis and spiral ligament of the chinchilla.

This study was designed to investigate the cellular distribution and ultrastructure of melanin pigment in the stria vascularis and spiral ligament of the chinchilla cochlea. Typical dendritic melanocytes containing homogeneously distributed eumelanin granules were observed in the spiral ligament. In the stria vascularis melanin was found to occur in three types of cells (heavily pigmented cells that appear to be melanocytes, intermediate cells and basal cells). The melanocyte-like cells contain pigment globules composed of melanin granules, granular matrix and occasional lipid droplets in a configuration similar to that of neuromelanin. These cells are morphologically distinct from intermediate cells which contain sparsely distributed, small, dense granules apparently composed of melanin. The intermediate cells show a positive DOPA reaction and portions of the intermediate cell GERL system display intense acid phosphatase reactivity. The basal cells of the chinchilla stria were also found to contain occasional clusters of melanin granules. It is hypothesized that the basal cells may acquire melanin by donation from the other pigmented cells of the lateral cochlear wall.

Animals↗
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Effects of middle ear ventilation on cholesteatoma development in experimental animals.

This study was designed to evaluate the effect of middle ear ventilation on cholesteatoma formation following propylene glycol application in experimental animals. Fifteen chinchillas had stainless steel ventilation tubes chronically implanted in their bullae and 60% propylene glycol was subsequently instilled into the middle ear cavities. The animals were kept alive for 4 weeks, during which time the middle ear pressure was monitored tympanometrically and the tubes were frequently inspected to verify patency. Of the 30 ears in the study, 20 (66.6%) developed middle ear cholesteatoma--a rate of occurrence comparable to that found in earlier studies in which middle ear ventilation was not provided. These results indicate that negative middle ear pressure is not a necessary factor for cholesteatoma development following application of chemical irritants in experimental animals.

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A direct current plasma emission spectrometric procedure for the assay of silicon in urine.

A method for the assay of silicon in urine has been developed using direct current plasma emission spectroscopy. Urine is directly aspirated into the argon plasma, and the silicon emission is measured at 251.6 nm. There is a moderate matrix effect which is not compensated by the addition of lithium chloride as an ionization suppressor. The use of calibration standards in an urine-like matrix gives the best analytical results as documented by serial dilution and standard addition studies. The method is linear over the entire range of urine concentrations normally encountered (0 to 50 mg per L). The lower detection limit is 0.05 mg per L and the coefficients of variation at the 2.7 mg per L and 5.9 mg per L levels are 5.8 percent and 11.5 percent, respectively. Urine from ten randomly chosen volunteers shows a considerable between subject variation in silicon concentration (mean 12.5 +/- 8.3 mg per L, range 1.8 to 51.6 mg per L) which is positively associated with vegetable intake. Urine from 39 hospital patients on a standardized diet shows much less variation in concentration (mean 4.1 +/- 3.2 mg per L, range 0.1 to 18.6 mg per L), indicating that the urine silicon assay is likely to be useful in metabolic studies only if diet is controlled.

Diet↗