Passive stabilization of capillary bridges in air with acoustic radiation pressure.

Long liquid capillary bridges are normally unstable because of the growth of a mode where one end becomes slender while the other becomes rotund. This Rayleigh-Plateau instability was suppressed for weightless bridges on NASA's KC-135 aircraft by placing the bridge in an acoustic standing wave. With an appropriate acoustic wavelength and amplitude the radiation pressure automatically squeezes more on the rotund portion of the bridge so as to suppress the growth of the relevant capillary mode. Stabilization is a natural consequence of the interaction with the steady sound field.

Quantitative analysis of rat inner ear blood flow using the iodo[(14)C]antipyrine technique.

A number of different qualitative and quantitative techniques have been used to measure inner ear blood flow and all have required that the animal be anesthetized. It is well known that anesthesia can cause a variety of circulatory as well as other systemic changes. In this study, we have employed a technique commonly used for quantifying brain blood flow, the iodo[(14)C]antipyrine technique ([(14)C]IAP). Unlike other techniques, [(14)C]IAP can be used in unanesthetized animals under conditions that are nearly normal, it is non-invasive, it can be used reliably in regions of low local blood flow, and data can be acquired from both the periphery and central nervous system. Results show that blood flow to the lateral wall of the basal turn of the cochlea (387 +/- 19 microl/g/min) is significantly higher (P<0.001) than that of the utricular macula (189 +/- 23 microl/g/min), horizontal (186 +/- 22 microl/g/min), superior (185 +/- 22 microl/g/min), or posterior canal crista (185 +/- 25 microl/g/min). Surprisingly, blood flow to all of the vestibular end-organs is remarkably similar. The use of this technique should allow pharmacological experimentation on inner ear blood flow without the unknown complications of anesthesia or invasive procedures.

Nonadrenergic innervation of the rat laryngeal vasculature.

In order to gain a better understanding of the central and local control of laryngeal blood flow, the vascular innervation to the rat laryngeal muscles was examined. To visualize the vascular network, the animals were perfused with a gelatin/India ink solution. The larynges were removed and fixed. The superior laryngeal, cricothyroid, and inferior laryngeal arteries (all branch off the superior thyroid artery) were dissected in continuity into their respective muscles. Specimens were reacted in toto using immunohistochemical techniques for the presence of neuropeptide-Y (NPY), vasoactive intestinal peptide (VIP), calcitonin gene related peptide (CGRP), and neuronal nitric oxide synthase (NOS-1). Results show that all of the laryngeal vasculature is richly innervated by fibers containing these peptides. Qualitatively, the most prominent of these is NPY in association with the superior and the inferior laryngeal arteries, followed by VIP and NOS-1, and finally CGRP distributed equally on all the vessels. Immunopositive fibers are found along the entire course of the feeding arteries, beginning with the superior thyroid artery and continuing down to small arterioles into the terminal vascular beds. These peptides can act as vasodilators, vasoconstrictors, and/or neuromodulators and may work synergistically or antagonistically with other transmitters in controlling laryngeal blood flow. Their effects are dependent on the specific vascular bed in question, that is, in some areas they are vasodilators, in others vasoconstrictors, and in other neuromodulators. What effects they have on the laryngeal vasculature and how they interact within the larynx have yet to be determined.

Comparison of the vascular innervation of the rat cochlea and vestibular system.

In order to gain a better understanding of the neuronal and local control of inner ear blood flow, the vascular innervation to the rat cochlea and vestibular system was examined. Specimens were removed in toto beginning at the basilar artery extending to the anterior inferior cerebellar artery, labyrinthine artery, common cochlear artery, modiolar artery and anterior vestibular artery. When possible the vessels were dissected in continuity through the cribrose area. The vestibular endorgans were also removed. Specimens were examined using immunohistochemical techniques for the presence of vasoactive intestinal peptide, neuronal nitric oxide synthase, neuropeptide-Y, substance P and calcitonin gene related peptide. Results show that the vasculature to the cochlea and vestibular portion of the inner ear receive similar types of nonadrenergic innervation, that within the vestibular endorgans, only CGRP and SP were found in the neuroepithelium or in association with vessels, and that within the vestibular system, the majority of the vascular innervation appears to stop at or near the cribrose area. In the cochlea however, it extends to include the radiating arterioles. These findings suggest that cochlear blood flow is under finer control and that neuronally induced changes in blood flow may have a more global effect in the vestibular periphery.

Aging rat vestibular ganglion: II. Quantitative electron microscopic evaluation.

This laboratory has shown that age-related vestibular ganglion cell loss does not occur in the Wistar rat as it does in humans. However, in that study, intracellular changes were evident. The purpose of the present study was to quantitate some of these changes. The volume densities of mitochondria, rough endoplasmic reticulum (RER), Golgi apparatus, and aging pigment, as well as the diameter of the vestibular ganglion cells, of young (3 to 5 months) and old (24 to 31 months) female Wistar rats were determined by electron microscopy and stereological techniques. The data show a significant decrease in the volume densities of mitochondria (11.4%), Golgi apparatus (8.1%), and RER (8.9%), a significant increase in aging pigment (327%), and no change in mean profile diameter. These results suggest a decreased capacity for oxidative metabolism and protein synthesis that may reflect a decrease in the number of hair cells innervated by each ganglion cell and/or in the number of central connections. In either case, these findings suggest impaired metabolic and functional capabilities.

Glucose utilization of the rat vestibular end organs: a quantitative 2-deoxyglucose study.

The local metabolic rate of glucose utilization (LMRglc) for the rat vestibular end organs was determined with a modification of the [14C]deoxyglucose method. Data are expressed as micromoles per 100 g per minute +/- SEM. Results indicate that the LMRglc is similar within the utricle (40.3 +/- 3.2) and saccule (41.2 +/- 5.5) and significantly higher than that for the superior (20.1 +/- 2.9), posterior (25.4 +/- 2.0), or lateral canal (22.0 +/- 2.6) ampullae. These differences in LMRglc may be related to differences in the ratios of sensory to nonsensory cells, dark cell distributions, response to acoustic stimulation, or activity levels during the experimental period. Given the high blood flow rates reported for the vestibular end organs by Lyon and coworkers, a much higher LMRglc was expected. Together, these data would suggest that delivery of metabolites is not a primary regulating force for vestibular blood flow. Instead, the primary reason for a high blood flow rate may be waste removal, the maintenance of pH, ion balance, and/or temperature.

Ultrastructural changes in superior vestibular commissural neurons following vestibular neurectomy in the cat.

The ultrastructural changes of the feline superior vestibular commissural neurons (CNs) were quantitatively assessed 8 weeks following ipsilateral vestibular neurectomy. Results indicated a slight degeneration of synaptic profiles (SPs; 25%) representing the primary vestibular afferent input onto CN soma. The synaptic vesicles of the remaining SPs, which likely originate from the cerebellum and the contralateral CNs, were smaller and rounder, suggesting a transition from an inhibitory to an excitatory mode of response. The SP loss had little impact on the CNs' capacity for protein synthesis and structural maintenance, since there was no change in the volume fraction of intracellular organelles. These data suggest that CNs do not degenerate and are likely functional after vestibular compensation. These findings support the role of the commissural pathway in vestibular compensation as proposed by Galiana et al, which is based on the assumption that the intervestibular commissural connections remain intact following vestibular neurectomy.

Morphologic changes in superior vestibulo-ocular neurons and vestibular nerve following labyrinthectomy in the cat.

Morphologic changes in ipsilateral superior vestibulo-ocular neurons (SVON) and the vestibular nerve were measured in 4 cats 8 weeks after labyrinthectomy and 4 cats 1 year after labyrinthectomy. There is a 20% decrease in SVON size and 30% decrease in rough endoplasmic reticulum and ribosomes with no change in the volume fractions of Golgi apparatus or mitochondria. In the central nervous system degeneration of the vestibular nerve terminals ipsilateral to the labyrinthectomy was represented by a 25% loss of synaptic profiles (SP) on SVON at 8 weeks and 57% loss of SP at 1 year after labyrinthectomy. There was no significant loss of fiber number in the vestibular nerve at 8 weeks post lesion but a 35% loss of fibers primarily of the large size at 1 year post lesion.

Rat utricular macula: blood flow and stereological assessment of capillary morphology.

Vascular compromise has long been proposed as a cause of inner ear disorders. However, the examination of blood flow and its control mechanisms in the vestibular system has been very limited. Combining stereological techniques with the microsphere injection technique, capillary morphology and regional blood flow were determined for the rat utricular macula. Results are as follows: total utricular blood flow 0.158 +/- 0.078 microL/min; blood flow to the neuroepithelium (excluding nerve) 0.0995 +/- 0.046 microL/min; blood flow per unit volume 7.71 +/- 4.31 microL/min per cubic millimeter, neuroepithelial volume 0.01344 +/- 0.0018 mm3; absolute capillary surface area 0.159 +/- 0.039 mm2; mean capillary diameter 5.84 +/- 0.56 microns; absolute capillary length 8.45 +/- 1.6 mm; and capillary lumen volume fraction 0.0175 +/- 0.004. Comparisons to previous data for the posterior canal ampulla indicate that the capillary diameter in the rat utricular macula is smaller; the capillary length is greater; and the end organs are similar with respect to neuroepithelial volume, capillary surface area, and blood flow. The size of the microsphere used in the present study (9.21 microns), in comparison to the mean capillary diameter (5.84 microns) of the utricular neuroepithelium, would indicate that the blood flow data likely represent a minimum value. These findings indirectly indicate that the utricular macula metabolic rate is greater than that of the posterior canal crista, and that there is variation from end organ to end organ in mean capillary diameter.

Blood flow and assessment of capillaries in the aging rat posterior canal crista.

Vascular change has been proposed as an etiological factor in inner ear aging and in several inner ear disorders. Moreover, some successful medical management of the episodic vertigo and tinnitus associated with Ménière's disease has been directed toward pharmacologically increasing blood flow, changing vascular permeability or ion homeostasis. While there are many studies of cochlear capillary morphology and blood flow, there are very few examining these variables in the vestibular system and none with respect to aging. The purpose of this study was to examine the rat posterior canal ampullary crista for age-related changes in blood flow and capillary morphology. By combining stereological techniques with microsphere injection, we have determined that in the rat posterior canal crista there is a statistically significant age-related decrease in blood flow (75%), mean capillary diameter (31%), and volume fraction of capillary lumen (31%). There is also an overall 18% decrease in the volume of the ampullary crista, a 72% decrease in blood flow/unit volume and a 36% increase in capillary length/unit volume. There were no significant changes in the capillary surface area/unit volume, the absolute capillary length, or the absolute capillary surface area. These data suggest impaired blood flow and degenerative loss of the ampullary crista may be relate to impaired end organ function.

Residual effects of tracer in sequential double label deoxyglucose studies.

The validity of sequential double label deoxyglucose (DG) determinations of local metabolic rate for glucose (IMRglc) was examined by quantifying the degree of trapping of residual first DG tracer during the second experimental period. One sciatic nerve was repetitively stimulated for 25 min, beginning either at the time of the DG injection or 25 min later. IMRglc in the ipsilateral dorsal horn of the lumbar spinal cord was found to be 105% and 56%, respectively, greater than that of the contralateral unstimulated side. Attempts to lower the body burden of radioactive DG by exchange blood transfusion failed to reduce this delayed effect. These data indicate that residual effects of the first tracer could obscure possible differences in IMRglc between two sequential experimental states.

Quantitative ultrastructural study of cat abducens interneurons.

Abducens interneurons project to the medial rectus subdivision of the contralateral oculomotor nucleus and have a role in the mediation of horizontal conjugate gaze. Two types of interneurons have been reported based on shape (fusiform and circular) and differences in organelles. In this study, 41 abducens interneurons from three young adult cats were examined in the transmission electron microscope and were classified, on the basis of eccentricity (e), as circular (e less than 0.82; N = 18) or fusiform (e greater than or equal to 0.82; N = 23). The volume fraction of nucleus, nucleolus, mitochondria, rough endoplasmic reticulum, polyribosomes, and Golgi complex and the number of synaptic profiles per 100 microns of membrane were determined. Although there is a qualitative difference in these cell types, statistical analyses indicate no significant differences in organelle content, mean area, number of synaptic profiles per 100 microns of membrane, or diameter. While the differences in shape may possibly indicate different functional groups, this notion is not supported by the variables examined or by physiological studies.

Ultrastructural changes in contralateral superior vestibulo-ocular neurons one year after vestibular neurectomy in the cat.

Twenty contralateral superior vestibulo-ocular neurons (SVON) from 3 cats were studied morphologically one year after a right vestibular neurectomy. Eighteen SVON contained a smooth or slightly crenated nuclear membrane, a 63% loss of synaptic profiles (SP) and a 22% decrease in size compared to control SVON. Two cells contained nuclear membrane invaginations, a 40% loss of SP and a 31% size decrease compared to control SVON. The volume fractions of rough endoplasmic reticulum and ribosomes were decreased in these two cell groups but no change was noted in Golgi apparatus and mitochondria. These contralateral SVON reached a size, innervation density and content of organelles similar to ipsilateral SVON at one year following vestibular neurectomy.

Ultrastructure of cat superior vestibular commissural neurons.

The ultrastructure of the feline superior vestibular commissural neurons (CNs) was studied after labeling by contralateral injection of horseradish peroxidase. These small spindle-shaped cells are found in clusters oriented in a rostrocaudal, dorsoventral or lateromedial direction. The CNs have a cleft nucleus, with the majority of nerve terminals contacting the CN near the emergence of polar dendrites. Polarization of the afferent synaptic profiles suggests a bidirectional nature of inputs to CNs by the vestibular nerve, contralateral CNs, and/or cerebellar systems. One type of labeled cell does not conform to this pattern, instead resembling a vestibulo-ocular neuron. Hence, it may function as a commissural and a vestibulo-ocular neuron. Characterization of different types of synapses, based on the size and eccentricity of their synaptic vesicles, indicates a continuum rather than separate populations. Volume fraction of intracellular organelles showed a larger volume fraction percent of polyribosomes in larger cells. Since this organelle is involved with protein synthesis, this finding may indicate that larger CNs have a more extensive dendritic tree.

Ultrastructural changes in contralateral vestibulo-ocular neurons following vestibular neurectomy in the cat.

Twenty contralateral superior vestibular vestibulo-ocular neurons (SVON) from 4 cats were studied morphologically 8 weeks after a right vestibular neurectomy. Nine SVON demonstrated a 35% loss of somal synaptic profiles (SP), normal nuclear and cytoplasmic size, but a slight decrease in organelles responsible for protein synthesis (rough endoplasmic reticulum and polyribosomes). Eleven SVON showed an 82% loss of SP, decrease in cell and nuclear size, and significant reduction in rough endoplasmic reticulum (RER) and polyribosomes. These transneuronal SVON changes are presumed to be the result of commissural pathway degeneration caused by the vestibular neurectomy.

Quantitative histochemical studies on the cat infrahyoid muscles.

The intrinsic laryngeal muscles have been reported to be composed of muscle fibers that have unusual physiologic, morphologic, and biochemical characteristics, and it has been suggested that the relatively unique differentiation of these muscle fibers is the result of their specific activity patterns. Because the infrahyoid muscles are recruited for some of the same laryngeal functions, it was of interest to determine if they also included unusual fiber types. In order to examine this possibility, microdensitometry was carried out on type I, type IIA, and type IIB fibers in the cat sternohyoid, sternothyroid, and thyrohyoid muscles using histochemical techniques for a variety of enzymatic markers of oxidative and glycolytic capacity and for fiber size. It was found that the infrahyoid muscles were composed of muscle fibers having enzyme profiles generally similar to those of fiber types in the limb muscles.

Blood flow and capillary surface area of rat posterior canal ampulla.

Vascular disorders have often been proposed to explain disorders of the inner ear, in both the cochlear and vestibular systems. While the cochlea has been extensively studied, little work has been done on vestibular blood flow. Existing studies have reported only total vestibular blood flow, using microspheres. By combining the physiologic technique of microsphere injection with new developments in morphologic stereology studies, data on end-organ blood flow (excluding nerve; 0.074 +/- 0.027 microliters/min; 5.99 microliters/min/mm3), capillary surface area (10.87 mm2/mm3), mean capillary diameter (9.64 microns), and end-organ volume (0.013 mm3) was determined for the posterior canal ampulla of young Fischer 344 rats. Results indicate an anatomic basis for increases in blood flow with CO2 breathing, and provide an assessment of appropriate microsphere size for vestibular blood flow studies. By allowing comparison of blood flow and capillary parameters related to surface area and volume, this new method of blood flow study will allow more meaningful data to be collected on the vestibular system.

Mitochondrial volume density of Schwann cells associated with rat vestibular ganglion cells.

The purpose of this study was to quantitate the mitochondrial volume density (MVD) within Schwann cells associated with vestibular ganglion cells in the female Wistar rat. Results show that this type of Schwann cell (SC) has a significantly higher MVD (19.4% +/- 1.9) than that reported for myelinating SC of peripheral nerve (1-5%). This large difference in SC MVD may be related to the energy requirements needed to maintain the local ion homeostasis around the ganglion cells given the environmental differences created by the different barrier systems of these regions of the nervous system.