Biomedical subjects

J Prazma

Publications and source records attributed to J Prazma.

At least 55 records · Page 3Linked to original sources

PubMed1992

Glyoxylic acid in the study of autonomic innervation in the gerbil cochlea.

The autonomic innervation of the inner ear has been investigated earlier, yet questions concerning the origin, function, extent, and distribution of sympathetic nerves in the cochlea still remain unanswered. This study investigates the extent and distribution of adrenergic nerves in the cochlea. Our procedure combines the glyoxylic acid method of catecholamine fluorophore identification with rapid dissection, decalcification, and whole-mount slide preparation techniques to topographically trace the adrenergic innervation of the cochlear infrastructure. We have demonstrated that perivascular adrenergic innervation extends beyond the immediate branches of the modiolar artery and reaches into radiating arterioles. These findings also suggest the possibility of segmental regulation of cochlear blood flow.

Adrenergic Fibers↗

PubMed1991

Bioelectric properties of gerbil middle ear epithelia.

Biochemical analysis of middle ear effusions provides indirect evidence of epithelial function, but no direct studies of middle ear epithelial function have been published. This study uses cell culture techniques to study the bioelectric properties of these cells and their response to pharmacologic agents. Middle ear epithelial cells were isolated by protease and DNase digestion and cultured on collagen matrices. A transepithelial potential difference (PD) measured by calomel half cells peaked by day 8 in culture (PD = -8.6 +/- 1.6 mV). Resistance and short-circuit current (ISC) were calculated to be 307 +/- 46 omega/cm2 and 28 +/- 4.1 A/cm2, respectively. At peak PD, cultures were mounted in flux chambers (Ussing), and pharmacologic agents were applied. Amiloride (10(-4) mol/L), an inhibitor of Na transport, decreased ISC by 52.3% +/- 4.9% but had no effect when added basolaterally. Carbachol (10(-4) mol/L), a cholinergic agonist, had no effect when added to the apical bath but increased ISC by 62.9% +/- 12.4% when added basolaterally. Isoproterenol (10(-4) mol/L), a beta-adrenergic agonist, increased ISC by 4.8% +/- 1.8% when added apically but had no effect when added basally. These results indicate that the epithelium lining the middle ear plays a role in regulating the quantity and composition of liquid in the middle ear by ion transport and that cell culture may be useful in studying this phenomenon.

Amiloride↗

PubMed1991

Inner ear damage secondary to diabetes mellitus. I. Changes in adolescent SHR/N-cp rats.

The association between diabetes mellitus and hearing impairment has been debated in many previous studies. The spontaneous hypertensive/NIH-corpulent (SHR/N-cp) rat has been shown to be a unique genetic model for non-insulin-dependent diabetes mellitus. Seventeen diabetic and 17 control young male rats were divided into groups according to diet and phenotype. The rats were fed either 54% of sucrose or 54% starch diets for 3.5 months and killed at 5 months. The cochleas were fixed, decalcified, dissected, and stained for hair cell counting. A significant loss of outer hair cells was noted in the diabetic obese (SHR/N-cp) animals when compared with the control obese (LA/N-cp) animals in every group. Although no significant difference was noted between the diabetic obese (SHR/N-cp) animals receiving the starch and sugar diets, the diabetic obese (SHR/N-cp) animals were more severely affected than the nondiabetic lean (SHR/N-cp) rats.

Animals↗

PubMed1990

Cochlear microcirculation. Effect of adrenergic agonists on arteriole diameter.

We used intravital fluorescent microscopy coupled with computerized video image processing to examine the cochlear microvasculature. In Mongolian gerbils the bulla was opened ventrally and a small window was made in the second turn of the cochlea. After fluorescein isothiocyanate-dextran administration, the radiating arterioles were video-recorded under X675 magnification. Computer determinations of arteriolar response to norepinephrine bitartrate (mixed alpha 1/alpha 2 agonist), phenylephrine hydrochloride (alpha 1 agonist), and UK 14,304 tartrate (alpha 2 agonist) were made at multiple dose levels over time. Findings were consistent with arteriolar constriction in response to alpha-adrenergic stimulation. The presence of alpha 1 and alpha 2 receptors was established, and a predominance of alpha 2 receptors in the cochlea was suggested.

Adrenergic alpha-Agonists↗

PubMed1990

Cochlear microcirculation in young and old gerbils.

Human postmortem studies as well as epidemiologic investigations have implicated the peripheral vascular system as one of the etiologic factors of presbycusis. This study uses the surface dissection microsphere method for regional cochlear blood flow analysis and morphometric techniques for quantifying capillary density in the stria vascularis. In this study 11 old and 10 young gerbils were used. Our results indicate that blood flow in the cochlea was decreased in the old gerbils. This decrease was most obvious in the lateral portion (stria vascularis). The decrease of blood flow in older animals was clearly not related to loss of strial capillaries with aging. The decreased flow to the lateral portion must arise from either decreased perfusion pressure or from increased vascular resistance. This decreased blood flow in the aged animals supports a vascular theory of presbycusis.

Aging↗

PubMed1990

Student Research Award 1990. Catecholaminergic innervation of the inner ear.

Cochlear blood flow has been shown to be controlled, in part, by the sympathetic nervous system. We have used immunocytochemical staining for tyrosine hydroxylase (TH) to further demonstrate the extent of catecholaminergic innervation of the cochlea. Deeply anesthetized Mongolian gerbils were systemically perfused with phosphate-buffered saline, followed by 4% paraformaldehyde. The cochleae were dissected out and post-fixed for 3 hours in 4% paraformaldehyde. They were then incubated in anti-TH antibody and subsequently processed using the avidin-biotin immunoperoxidase method. Microscopic examination of whole-mounted tissue revealed many immunoreactive fibers on the spiral modiolar artery. TH-positive fibers have also been found on both radiating arterioles and radial collecting venules, which has not been previously reported. With innervation of these small vessels, blood flow in the cochlea may be segmentally controlled. We also further describe the organization of TH-positive fibers in the osseous spiral lamina.

Animals↗

PubMed1990

Analysis of blood flow in the tympanic membrane: the use of intravital fluorescence microscopy.

The successful healing of the tympanic membrane (TM) following myringotomy or tympanoplasty is dependent upon the maintenance of the blood supply to the injured area of the TM. The blood supply of the TM is derived from the manubrial plexus and the peripheral plexus of vessels. This study concentrated on measuring blood flow derived from the manubrial vessels. The TM of the guinea pig was used as an in vivo model. Ten Outbred Hartley guinea pigs were anesthetized with Inactin 100 mg/kg, the common carotid artery cannulated, and FITC-dextran 150 injected intra-arterially. Blood pressures (mean 66.0 mmHg +/- 5.0 mmHg) and heart rates (330 bpm +/- 12.0 bpm) remained relatively constant throughout the experiment. Following injection of FITC-dextran 150, the TM was visualized under fluorescence microscopy and images recorded by video recorder; measurements of vessel diameter, blood velocity, and blood flow were made. Analysis of the in vivo studies revealed blood flow in the tympanic membrane to travel in two directions: down the manubrial artery towards the periphery and up the manubrial veins from vessels in the periphery. The manubrial artery divides and branches into a series of arcading vessels that extend towards the periphery of the TM. Manubrial artery diameter was measured (mean 0.0521 mm +/- 0.0004 mm) and blood flow calculated (mean 0.0439 mm3/min +/- 0.0007 mm3/min). Blood flow from the manubrial artery supplying the superior quadrants (0.18 mm3/min +/- 0.01) was statistically greater when compared to the blood flow in the inferior quadrants (0.08 mm3/min +/- 0.007) (p less than .001).

Animals↗

PubMed1989

Combined effects of aspirin and noise in causing permanent hearing loss.

Several authors have investigated the interaction of noise and aspirin in hearing loss, with conflicting results. We studied the combined effects of noise and high doses of aspirin on hearing in rats. Thirty-eight Sprague-Dawley rats were divided into the following five groups: (1) controls; (2) aspirin only; (3) noise only; (4) 8-day per 200 mg of aspirin per noise; and (5) 12-day per 200 mg of aspirin per noise. Auditory brain-stem-evoked responses were measured in each animal prior to, 24 hours after, and 3 weeks after aspirin and noise exposure. The animals were killed and hair cells were counted in 200-micron segments and expressed graphically. Results showed significant differences in permanent threshold shift and hair cell loss between all noise-exposed animals and non-noise-exposed animals. There was also a significantly greater amount of hair cell loss in group 5 when compared with groups 3 or 4. The 12-day per 200 mg of aspirin per noise regimen (group 5) also proved to be fatal for 6 of 15 of these animals, and caused significant weight loss in the survivors. No weight loss or deaths were noted in any other group.

Animals↗

PubMed1989

Measurement of cochlear blood flow: intravital fluorescence microscopy.

A technique is described for directly observing in vivo cochlear microvasculature in the gerbil for physiologic and experimentally induced changes in vessel diameter and blood flow velocity. Measurements are made from computer processed video images of surgically exposed microvessels. These images are obtained using intravital fluorescence microscopy (IFM) with epi-illumination. The Mongolian gerbil is an ideal animal model for circulatory studies of the inner ear. It has a stable heart rate and blood pressure under urethane/alpha-chloralose anesthesia and its cochlea is surgically accessible. A window is created over the feeding artery (anterior inferior cerebellar artery) and over the stria vascularis of the second turn of the cochlea, atraumatically exposing radiating arterioles and strial capillaries. Our system of IFM provides images that are videorecorded, digitally analyzed with a computer image processor, and enhanced according to the type of measurement desired. Velocity measurements are obtained by tracking plasma gaps or single fluorescent labeled red blood cells through successive frames of the videorecorded images. This experimental technique allows us to analyze circulatory responsiveness to a variety of vasoactive drugs administered regionally to the cochlea in concentrations not affecting systemic circulation.

Animals↗

PubMed1988

Cochlear blood flow. The effect of six hours of noise exposure.

The effect of six hours of high-frequency, high-intensity noise exposure on cochlear blood flow (CoBF) was investigated in adult gerbils. The CoBF was measured by microsphere-surface preparation methods. Intracardiac injection of the microspheres (diameter, 11.1 microns; Dupont/New England Nuclear Research Products, Boston) was performed in the last few minutes of the sixth hour of continuous noise exposure, and reference blood was withdrawn from the iliac artery at a rate of 0.165 mL/min. The number of microspheres in the investigated tissue was assessed by direct counting under a microscope. The number of microspheres in the reference blood was counted by a Coulter counter. These experiments have shown that CoBF at the end of six hours of continuous noise exposure does not significantly differ from the CoBF in control animals.

Acoustic Stimulation↗

PubMed1987

Cochlear blood flow. The effect of noise at 60 minutes' exposure.

The effect of 60 minutes of exposure to high-frequency (10- to 40-kHz), high-intensity (115-dB) noise on the cochlear blood flow (CoBF) was investigated in adult gerbils. The CoBF was measured with a newly improved microsphere method. The number of microspheres in cochlear tissue that had been dissected by the surface preparation technique was assessed by direct counting. Our experiments have indicated that the CoBF is elevated even after 60 minutes of noise exposure. This was true particularly in the areas where these frequencies stimulate the cochlea. The noise also increased CoBF in the opposite ear in areas not corresponding to the stimulation frequencies (second and third turn). This phenomenon is under further investigation.

Animals↗

PubMed1987

Use of steroids and a long-acting vasoconstrictor in the treatment of postintubation croup. A ferret model.

There is little in the literature to support recommendations for the use of steroids and vasoconstrictors in the treatment of postintubation croup. We developed a ferret model to study this condition. Ninety-eight ferrets were used in these experiments, which were undertaken to evaluate the efficacy of steroids and/or a long-acting vasoconstrictor, to develop dose-response curves for dexamethasone sodium phosphate if it proved efficacious, and to evaluate the possible synergistic effects of combination therapy. With this animal model, we were able to document a statistically significant early effect of dexamethasone sodium phosphate, but only when administered in large doses (greater than 0.5 mg/kg). Our data also support the tapering of these large doses within a 20-hour period. The long-acting vasoconstrictor oxymetazoline hydrochloride has a clear and statistically significant beneficial effect that is apparent by 20 hours and continues through 40 hours. We did not find any additive or synergistic effect of the combination of dexamethasone and oxymetazoline. Further studies are underway in our laboratory to elucidate other aspects of this interesting syndrome.

Animals↗

PubMed1987

Comparative morphometric analysis of cochlear vessels in Wistar-Kyoto rats, spontaneously hypertensive rats, and aged spontaneously hypertensive rats.

Vessel density and the ratio of the tissue area to the vessel surface area were studied by morphometric analysis techniques in normal rats, spontaneously hypertensive rats (SHR), and aged spontaneously hypertensive rats (aged SHR). Horseradish peroxidase was injected intravenously and the animals were killed 10 minutes later. The temporal bones were harvested, fixed in glutaraldehyde, and decalcified in 10% ethylenediamine tetraacetic acid (EDTA). After 7 days of decalcification, the cochleas were dissected and incubated with a diaminobenzidine tetrahydrochloride solution. Sections with stained vessels were projected onto the digitizing plate with the help of the camera lucida. The computer was used to calculate tissue area, vessel length, and vessel surface area. A statistically significant increase (p less than 0.05) in both the tissue area to vessel length ratio and the tissue area to vessel surface area ratio was demonstrated in the SHR and the aged SHR groups when compared to the WKY in the stria vascularis. No statistically significant difference was found between the two SHR groups. These data show a decrease of the vessel density in the capillary beds of the stria vascularis in spontaneously hypertensive rats. No statistically significant difference was found in the diameters of the capillary among the three groups.

Animals↗

PubMed1986

Cochlear blood flow in the rat. A comparison of 10- and 15-micron spheres.

The microsphere method combined with surface preparation dissection is described for measuring cochlear blood flow in the rat. Two sphere sizes, 10 and 15 micron, were compared. No difference between the two sizes was found for measuring total cochlear blood flow. Shunting of the 10-micron spheres appeared to be similar to shunting of the 15-micron spheres and thus was minimal. However, the 15-micron spheres distributed poorly to the apical cochlea, especially the spiral portion. The 10-micron sphere was less toxic, allowing larger numbers of spheres to be infused. Consequently, more 10-micron spheres lodged in the cochlea, which is important for reducing random error. For these reasons, we recommend the 10-micron sphere, as opposed to the 15-micron sphere, for studying cochlear blood flow in the rat.

Animals↗

PubMed1984

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.

Animals↗

PubMed1983

Cochlear blood flow. Effect of noise.

Cochlear blood flow as investigated in anesthetized gerbils exposed to high-frequency (10 to 40 kHz), high-intensity (113 dB sound pressure level noise for 13 minutes. Blood flow was measured using a newly developed technique, which combines the surface preparation dissecting of the cochlea with the microsphere method. Our experiments indicate that short-lasting, high-intensity noise exposure causes a highly significant elevation of the blood flow in noise-exposed inner-ear areas. On the exposed side, blood flow increase was observed in the first turn of the stria vascularis-supralis ossea. On the opposite side, which was exposed only through bone conduction, blood flow was significantly elevated only in the basilar membrane.

Animals↗

PubMed1982

Perilymphatic and endolymphatic PO2. Variations during anoxia, hyperoxia, and hypercapnia.

Cochlear microcirculation was studied with oxygen-sensitive microelectrodes simultaneously in all three scalas during anoxia, hyperoxia, and hypercapnia. The anoxia caused a sharp decline of Po2 in the scala media (SM), scala vestibuli (SV), and scala tympani (ST). Hyperoxia and hypercapnia resulted in an elevation of Po2 in all three scalas. During anoxia, the SM showed the earliest and largest decline in Po2, with the shortest recovery and reoxygenation time. When Po2 slopes (during anoxia) were compared, the SM to ST and the SM to SV were substantially different and remained different even when the partial pressures of oxygen quantified as oxygen in nanomoles. Our experiments also showed that changes in Po2 within the SM closely correlate with changes of endocochlear potential and BP.

Animals↗

PubMed1981

Effect of ethaverine hydrochloride on cochlear microcirculation.

The effect of ethaverine hydrochloride on cochlear microcirculation was observed in short-term experiments on 11 guinea pigs. In these experiments, the endocochlear PO2, endocochlear potential (EP), cochlear microphonic (CM) potential, and blood pressure (BP) were recorded. Endocochlear PO2 was measured polarographically by gold electrodes in the scala media. Ethaverine hydrochloride was administered by intravenous infusion for ten minutes in doses of 2, 5, and 10 mg/kg. These experiments demonstrated that ethaverine hydrochloride in doses of 5 and 10 mg/kg caused significant elevation of endocochlear PO2 for 35 to 90 minutes, even when the BP temporarily declined. At the same time, it was observed that this improvement of cochlear microcirculation coincided with an increase of the CM potential. Decrease of the EP is probably the result of BP decline and a direct action of ethaverine on EP generation.

Acoustic Stimulation↗