The vessels of the stria vascularis: quantitative comparison of three rodent species.

The stria vascularis (SV) was quantitatively compared in three species commonly used in auditory research: guinea pig, mouse and gerbil. Measurements were obtained for surface area, cross-sectional area, length, width and thickness of SV. Surface area and length were proportional to the overall size of the cochlea in each species, but there was no significant difference between species in mean cross-sectional area. In guinea pig and mouse, there was no significant difference in thickness (endolymphatic surface to spiral ligament) and a similar pattern was observed for width (Reissner's membrane to spiral prominence): the width of SV increased from the apical end to a point 80% of the distance from the apex, then decreased to the basal end of SV. The thickness of gerbil SV was significantly less (P less than 0.001) and there was less of a gradient in width as compared to guinea pig and mouse. The vessels of SV were compared in terms of vascular density (vessels per unit area), rbc density (red blood cells per unit area), R/V (rbc density/vascular density), inter-vessel spacing and vessel diameter. Highly significant (P less than 0.001) differences between species were found in vascular density, RBC density and vessel diameter, but there were no differences between species for R/V or inter-vessel spacing. The results of this study may reflect differences in the metabolic requirements of SV among different species.

In vivo capillary diameters in the stria vascularis and spiral ligament of the guinea pig cochlea.

Blood microvessels in the membraneous lateral wall of the cochlea were examined using intravital microscopic techniques. A video analysis system made serial diameter measurements at 1 micron intervals along the length of selected vessel segments during four experimental conditions. For each vessel segment, the serial measurements were statistically converted into a single diameter estimate, such that the flow resistance in a uniform vessel of this diameter would equal the resistance of the real non-uniform vessel. Nominal vessel diameters found (spiral ligament: 9-12 micron; stria vascularis: 12-16 micron) were nearly double those reported earlier in histological observations (Axelsson, 1968). During stimulation the largest diameter change seen was a 3.7% dilation (about 0.5 micron) in response to breathing 5% CO2 in oxygen. Theoretically, this change could reduce vascular fluid resistance by 16%, nearly enough to explain the observed flow increase of 20%. No diameter changes occurred for 5% CO2 in air despite a 50% flow increase, nor for air pressure pulses applied at the tympanic membrane. Round window electrical stimulation of 50 microA also produced dilation (less than 2.5%), but higher current levels were ineffective. In general, blood flow increases seen in this study could not adequately be attributed to the small lateral wall vessel diameter increases nor systemic causes, suggesting that lateral wall blood flow in these instances is dependent on control within the modiolus.

Tissue oxygen tension in the stria vascularis.

Tissue oxygen tension in the stria vascularis was successfully measured in cats using the polarographic technique. A correlation study using the differential coefficient between oxygen tension in the stria vascularis and systemic blood pressure proved that vascular autoregulation is present in the mean systemic blood pressure range between 40 and 80 mmHg. The anatomical findings and the response patterns to different gas inhalations indicated that the type of vascular regulation present is more closely related to chemical control than to auto-regulation.

Quantitative evaluation of pinocytosis of capillaries of the stria vascularis under normal and experimental conditions.

In order to examine evidence of high activity of pinocytosis in capillaries of the stria vascularis, quantitative morphometry of pinocytotic vesicles was carried out ultrastructurally by the horseradish peroxidase (HRP) tracer method. In guinea pigs, there was a significant difference between the stria vascularis and spiral ligament in the number of vesicles per micron 2 (p less than 0.05) and labelled vesicles per micron 2 (p less than 0.001). In normotensive control rats, the number of labelled vesicles per micron 2 in capillaries of the stria vascularis was significantly greater (p less than 0.001) than that of the spiral ligament. Results of acute hypertensive and acute hypotensive experiments both indicated that enhanced permeable capillaries of the stria vascularis showed no significant increase in the number of pinocytotic vesicles per micron 2, but that they showed a more significant increase in the number of labelled vesicles per micron 2 than non-enhanced permeable capillaries of the stria vascularis (p less than 0.01) and capillaries of the spiral ligament (p less than 0.001). These findings provide ultrastructural confirmation of our previous studies (4, 8, 9) that pinocytosis contributes to the high permeability of capillaries of the stria vascularis under normal and experimental acute hypertensive and acute hypotensive conditions.

Velocity of red blood cell flow in capillaries of the guinea pig cochlea.

Velocities of red blood cells (RBCs) in the lateral wall of the cochlea were determined in the anesthetized guinea pig from direct optical microscopic observations. Mean flow velocity of the blood was measured by timing the passage of a fluorescently-labeled subpopulation of RBCs across a measured capillary length. The optical observations were achieved using an intravital microscope equipped for epifluorescence and the measurements were derived from video images acquired with an image intensified television camera. In the third turn of the cochlea the velocity of RBCs differed significantly between two major classes of capillaries. The mean velocity in spiral ligament vessels was 0.12 mm/s while stria vascularis flow was slower (0.08 mm/s). In a typical animal, the range of velocities among different vessels of the ligament was 0.09-0.18 mm/s while it was 0.03-0.10 mm/s for stria vascularis vessels. Corresponding to this velocity difference, the apparent mean vessel diameters for the two types of vessels also differed. Spiral ligament capillaries were 9.3 micron while strial capillaries were 12.2 micron in diameter. Comparison of flow velocity in different turns of the cochlea indicated that the distribution of blood velocity throughout the cochlea lateral wall is constant.

Diabetes mellitus and hearing loss: clinical and histopathologic relationships.

We compared audiometric and clinical histories with findings in temporal bones of eight diabetics and ten normal controls matched for age and sex. The group with diabetes mellitus had significantly more hearing loss than the normal control group (p less than .01). Only patients with diabetes had microangiopathy. Patients with microangiopathic involvement of the endolymphatic sac had significantly greater hearing loss than patients without such involvement (p less than .01). Microangiopathy in the stria vascularis was highly significant in the diabetics (p less than .001); however, they did not have a significant hearing loss. Diabetic patients with basilar membrane microangiopathy had significantly lower percentages of histologically normal hair cells (p less than .05) and stria vascularis cells (p less than .05) and significantly greater hearing loss (p less than .01) than diabetic patients without such pathologic changes. Results of this study suggest that diabetic sensorineural hearing loss results from microangiopathic involvement of the endolymphatic sac and/or basilar membrane vessels.

Ultrastructural characteristics of capillaries entering and leaving the stria vascularis.

Capillaries entering and leaving the stria vascularis were surrounded by layers of basal cells and fibrocytes. The entering capillaries were surrounded by one or two thin basal cells, while the leaving capillaries were surrounded by four or five thicker and interdigitated basal cell layers. Moreover, the layers surrounding the leaving capillaries persisted further into the spiral ligament. Two kinds of filaments were observed in the basal cells, one thin and the other thick. Capillaries were observed to leak horseradish peroxidase before they entered and after they left the stria vascularis. Although the reaction product of horseradish peroxidase was observed in all perivascular spaces of leaving capillaries, very little or no reaction product was observed around some entering capillaries. It is speculated that the layers of basal cells and fibrocytes around entering and leaving capillaries control the vascularis, although the layers around leaving capillaries may be more contractile than those around entering capillaries.

The early postnatal development of the cochlear vasculature in the gerbil.

The blood vessels of the cochlea were studied from birth up to adult age in the gerbil. Even at birth the principal vascular arrangement could be identified in the external wall. However, the early circulatory mainstream appeared even more predominantly radial apico-basal over radiating arterioles-arteriovenous anastomoses-collecting venules than at later stages. At birth, only small sections of capillaries could be observed in the stria vascularis. Stria vascularis achieved its adult vascular appearance rapidly between 8-10 days after birth (DAB). The rapid development of stria vascularis immediately preceded the development of cochlear function and may have been related to the development of the ionic composition of endolymph. At birth the vessel of the basilar membrane showed many large vascular connections with the collecting venules in the scala tympani of the external wall but very few supplying and draining ramifications on the medial side of the vessel. This suggests that the vessel of the basilar membrane originates from the external wall vessels, not from the spiral lamina vessels as has previously been supposed. The peripheral vascular connections degenerated rapidly after birth. The vessel, being very large at birth, degenerated completely by 15 to 20 DAB, ultimately disappearing in the basal turn. The degeneration suggests that its major importance may be during embryonic stages, with great probability for the development of the organ of Corti.

Effects of noise and quinine on the vessels of the stria vascularis: an image analysis study.

Surface preparations of the stria vascularis from guinea pigs exposed to wide-band noise or intoxicated with quinine monohydrochloride dihydrate were studied by light microscopy and computerized image analysis in order to evaluate quantitatively the effects of these agents on two characteristics of the strial vasculature: vascular density and erythrocyte distribution. An image analyzer was used to measure the area of strial vessel lumen and erythrocyte distribution as a fraction of the total area of strial tissue under observation. The results demonstrate that changes in the strial vessels do occur in guinea pigs exposed to noise or given large doses of quinine. Localized vessel narrowings caused by swollen endothelial cells and possibly by contraction of pericytes were found in both experimental groups, but there was no apparent tonotopical relationship between these effects and the reduction in cochlear potentials. A significant reduction in the number of erythrocytes was found in all turns of the cochlea in both experimental groups. Although a significant difference in vascular density was found among turns of the cochlea in both experimental and control animals, there was no widespread change in vascular density as a result of either noise exposure or quinine treatment.

Effect of high intensity impulse noise on the vascular system of the chinchilla cochlea.

Changes in the vasculature of the chinchilla cochlea were quantitatively assessed 45 days after impulse noise exposure of either 155- or 160-dB peak sound pressure level. The condition of the vessels in the lateral wall and spiral lamina of each cochlea was evaluated in terms of 20 morphological parameters. Multivariate statistical analysis identified the parameters that were significantly affected by the noise exposure. Evaluation of these significant parameters indicated a net reduction in blood flow to the cochlea. All of the noise-exposed cochleas showed vascular changes when compared to controls, and the magnitude of these changes was related to the amount of hair cell loss. The vascular changes are presumed to be permanent.

Three cases of vascular problems in the human stria vascularis.

The histopathological findings of a study of temporal bones are reported. Each patient suffered from one of the following systemic vascular diseases: leukemia, hypertension, and diabetes mellitus. In each temporal bone, a differing strial pathology was observed: leukemic infiltration, dilatated strial vessels, and microaneurismata. Microvascular changes as seen in this study could make the human inner ear more vulnerable to inner ear traumata.

A morphometric technique for analysis of cochlear vessels.

A computer based system was developed for morphometric analysis of the cochlear lateral wall vasculature. Variables measured were vascular density, RBC density, vessel width, aggregation density, lumen compression count, WBC count and pigment density. Vessels were divided into three systems based on the lateral wall structures that they supplied. The results indicated that these three vessel systems were morphologically distinct in terms of their vascular density, RBC density, and vessel width. How these differences relate to functional needs of the lateral wall is discussed.

A morphometric study of microvascular pathology following experimental rupture of Reissner's membrane.

In a previous paper (this volume) we described a method for evaluating the cochlear microvasculature. This method was applied to the analysis of lateral wall tissue from chinchillas sacrificed 1 h, 24 h, 1 week and 3 weeks after surgical rupture of Reissner's membrane. The degree, direction, and time course of pathological changes seen in the microvessels were different for the system of stria vascularis vessels, the system of spiral ligament vessels, and the system of spiral prominence vessels. These results indicate that it is important to evaluate all of the lateral wall vessels rather than just the stria vascularis, and emphasize the importance of dividing the microvasculature into three independent systems, in order to obtain a clearer perspective on microvascular changes which occur following cochlear trauma.

Microvasculature of the stria vascularis in the round window area in the rat. A scanning electron microscopy study.

This paper reports the results of a scanning electron microscopy study of corrosion cast preparation of the vessels in the cochlea of the rat. This method confirms the general findings about the cochlear vascularization, but also gives the opportunity to study the detailed pattern of the vascular supply of the stria vascularis in the round window area. The basal end of the stria vascularis has a remarkably different vascular anatomy compared with the other areas of the cochlea. The possible role of the vessels in the round area is discussed.

Determination of the regional cochlear blood flow in the rat cochlea using non-radioactive microspheres and serially sectioned cochleas.

The regional blood flow to the rat cochlea has been studied using a method which combines the microsphere method with observation of serially-sectioned, plastic-embedded cochleas. Direct quantitation of the microspheres in a reference blood sample and in the different vascular areas of the cochlea allows the analysis of blood flow patterns with respect to the different capillary beds.

Computerized reconstruction of the regional blood flow in the rodent cochlea.

The regional blood flow in the cochlea has been studied by mapping the distribution of microspheres in 22 micron thick serial sections of plastic embedded rat and rabbit cochleas. Using a computer-assisted reconstruction technique, a graphic display of the microspheres in each cochlea is obtained. From this display, microspheres may be counted and their distribution may be observed both in relation to the different vascular areas and with respect to the length of the cochlea. This technique, coupled with quantitation of the microspheres in a reference blood sample, offers a method for calculating total and regional cochlear blood flow using non-radioactive microspheres. In addition, this technique allows analysis of blood flow patterns with respect to the different capillary beds along the length of the cochlea. Thus it may be possible to determine if regional blood flow displays a longitudinal gradient, as do other functional, morphologic and biochemical characteristics of the cochlea.

Increased capillary permeability of the stria vascularis to HRP, induced by experimental acute hypotension in rats.

Acute hypotension was produced in rats by using two experimental techniques: intravenous infusion of a ganglion-blocking agent (Arfonad), and venesection of a femoral vein. Horseradish peroxidase (HRP) was injected intravenously after each procedure, and subsequently observed in the inner ear by light and electron microscopy. In both experimental models, a large amount of tracer spread into the intercellular spaces, but it was halted by tight junctions bordering the stria vascularis. The endothelium exhibited a high distribution density of labelled vesicles, which suggested increased vesicular transport. There was no extravasation of HRP from capillaries in the spiral ligament in spite of the presence of some labelled pinocytotic vesicles. The present study was concerned with the discovery of enhanced capillary permeability of the stria vascularis under acute hypotension, as in the case of acute hypertension (Sakagami et al., 1984).

Measurement of cochlear blood flow--new technique.

A newly-developed procedure which combines the microsphere method with surface preparation dissection was employed in an investigation of blood flow in cochleas of anesthetized gerbils. In these experiments, 10.1 +/- 0.9 microns carbon-coated microspheres were injected into the left auricle of the heart and a reference blood sample withdrawn at 0.165 ml/min from the iliac artery. The blood flow in the lateral portion (stria vascularis, ligamentum spirale, and suprastria) was calculated to be 337.20, 184.00 and 24.75 nl/min; in the spiral portion (basilar membrane, lamina spiralis ossea, and limbus spiralis) it was found to be 85.40, 39.55 and 6.10 nl/min; and in the central portion (modiolus) it was found to be 256.55, 43.60 and 2.45 nl/min in the first, second and third turns, respectively. The total blood flow in the left and right membranous cochleas was 1062.70 and 896.60 nl/min, respectively. Averaged total blood flow in both ears was 979.60 nl/min. This is a first attempt to measure blood flow in the very small, functionally different areas of the cochlea. This work has shown that it is possible to measure and compare blood flow between the turns and between different functional parts within the turns.

Ultrastructural study of the effect of acute hyper- and hypotension on the stria vascularis and spiral ligament.

The effects of acute hyper- and hypotension on the stria vascularis and spiral ligament of the rat were studied electron microscopically with the horseradish peroxidase (HRP) tracer method. Acute hypertension was induced by i.v. infusion of methoxamine chloride (Mexan), and acute hypotension by i.v. infusion of a ganglion-blocker (Arfonad) and by venesection. In both acute hyper- and hypotensive experiments, a large amount of leaked HRP spread into the intercellular spaces until it was stopped by tight junctions bordering the stria vascularis. The stria capillary endothelium displayed a dense distribution of labelled vesicles, which suggests increased vesicular transport. There was no extravasation of HRP from capillaries in the spiral ligament, despite the presence of some labelled pinocytotic vesicles. The present paper deals with the discovery of enhanced capillary permeability of the stria vascularis under acute hyper- and hypotension, and makes comparison between acute hyper- and hypotension in order to define the function of the stria vascularis.