Biomedical subjects

J Prazma

Publications and source records attributed to J Prazma.

At least 37 records · Page 2Linked to original sources

PubMed1996

Effect of sodium nitroprusside on compound action potential thresholds in the gerbil cochlea.

The presence of active nitric oxide synthase (NOS) in the spiral ganglion cells of the cochlea suggests that the neuromodulator nitric oxide (NO) may play a role in hearing. This study investigated the effects of sodium nitroprusside (SNP), an NO donor, upon cochlear function mediated through its activation of guanylate cyclase. In gerbils, cochlear compound action potential (CAP) thresholds were recorded after cochlear perfusions of control and test solutions in four experimental groups. Perfusions were performed using the following: artificial perilymph solution (APS); the NO donor SNP; the guanylate cyclase inhibitor methylene blue (MB); and sodium dodecyl sulfate (SDS), which facilitates MB entrance into cells. SNP caused significant elevations of CAP thresholds from baseline (25 dB SPL +/- 1.54 dB to 64.3 dB SPL +/- 2.54 dB). SNP with MB also resulted in significant CAP threshold elevations (29.4 dB SPL +/- 4.27 dB to 38.1 dB SPL +/- 4.0 dB); however, these elevations were significantly lower than those seen in SNP perfusions without MB. Drilling perfusion holes and perfusion of APS, APS/SDS, and MB/SDS/APS solutions did not significantly affect CAP thresholds. These results suggest that the NO donor nitroprusside does affect cochlear neuromodulation and effects this mediation in part through NO activation of guanylate cyclase.

Action Potentials↗

PubMed1996

Nitric oxide: a mediator of endotoxin-induced middle ear effusions.

Using a rat model, the authors investigated the role of nitric oxide (NO) in endotoxin-induced middle ear effusion (MEE). After the eustachian tube was obstructed, the middle ear was transtympanically injected with 35 microL of either 1 mg/mL lipopolysaccharide (LPS) or LPS and 1 mmol/L N-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NO synthase. Over the next 6 hours, the fluid within the middle ear was collected every 2 hours, and the quantity of albumin in the fluid, an index of vascular leakage, was determined using enzyme-linked immunosorbent assay. L-NAME significantly reduced LPS-induced vascular extravasation into the middle ear. Inoculation of the ear with L-arginine, the substrate for NO synthase, reversed the effects of L-NAME. These results indicate that NO is a mediator of LPS-induced MEE. Therefore, inhibition of NO synthase may represent a novel approach to the treatment of otitis media with effusion.

Albumins↗

PubMed1996

Immunohistochemical localization of nitric oxide synthase activity in upper respiratory epithelium.

Nitric oxide (NO) production in the respiratory epithelium of the upper airways has recently been described. To better delineate the role of epithelial NO, the authors of this study attempted to identify the cell type responsible for the production of NO in rat tracheal epithelium and human nasal epithelium. They localized the activity of NO through immunohistochemical analysis with an antibody to L-citrulline, a marker for activity of the L-arginine-dependent nitric oxide synthase (NOS) pathway. Using anti-inducible NOS (iNOS) and anti-constitutive NOS (cNOS) antibodies, they also attempted to identify the specific NO isotypes that were present. The tracheal and nasal epithelium demonstrated strong immunoreactivity to citrulline in ciliated cells. The ciliated cells of the nasal turbinates demonstrated strong iNOS positivity, but no significant cNOS immunoreactivity. The study findings that iNOS activity is present in ciliated epithelial cells of rat and human upper respiratory epithelium suggest that NO may play a role in epithelial homeostasis and could potentially play a role in the pathogenesis of mucociliary dysfunction.

Animals↗

PubMed1995

An assessment of cochlear hair-cell loss in insulin-dependent diabetes mellitus diabetic and noise-exposed rats.

OBJECTIVE: The purpose of this study was to investigate if insulin-dependent diabetes mellitus causes degenerative changes in the inner ear and whether these changes are exacerbated by noise exposure. METHODS: Insulin-dependent diabetes mellitus was induced in male rats using streptozotocin (65 mg/kg of body weight, intravenously). Half the animals were exposed to 95 dB of random noise for 12 hours per day over a period of 6 months. The cochleae were removed, fixed, decalcified, dissected, and the hair cells counted. RESULTS: A significant loss of outer hair cells was exhibited in both noise-exposed groups; however, although there was no significant difference between these two groups, the noise-exposed diabetic animals had significant loss in more turns than did the noise-exposed control animals. The diabetic animals were not statistically different from the control animals. CONCLUSION: These results suggest that insulin-dependent diabetes mellitus may increase the hair-cell loss caused by noise overstimulation.

Animals↗

PubMed1995

Immunocytochemical localization of aspartate and glutamate in the peripheral vestibular system.

Controversy exists concerning the identity of the neurotransmitter in the mammalian peripheral vestibular system. Several candidates have been proposed, including the excitatory amino acids glutamate and aspartate and the inhibitory amino acid gamma-aminobutyric acid (GABA). Previous studies have demonstrated vestibuloneural electrophysiological activity associated with glutamate and aspartate. Paraffin sections of rat vestibular ganglia and end-organs were examined for the presence of glutamate-like and aspartate-like immunoreactivity. Our results demonstrate the presence of both aspartate-like and glutamate-like immunoreactivity in vestibular hair cells, peripheral vestibular nerve fibers, and vestibular ganglion cells. Minimal immunoreactivity was noted in the tissues surrounding these cells. These data add support to the hypothesis that the excitatory amino acids glutamate and aspartate are involved in vestibular neurotransmission.

Absorption↗

PubMed1995

Consumption of a high-galactose diet induces diabetic-like changes in the inner ear.

Diabetes mellitus is a disease that affects multiple organ systems. In our laboratory it has been shown that there is a significant loss of outer hair cells in genetically diabetic rats. Galactosemia can also produce diabetic-like changes. This study was performed to demonstrate whether these changes also occur in the cochlea. Three groups of Sprague-Dawley rats were used and fed either a control diet, a 50% galactose diet, or a 50% galactose diet with the addition of an aldose reductase inhibitor. After 6 months the animals were killed, and the cochleas were removed, fixed, and stained. Diabetes-induced damage was assessed by counting the hair cells and calculating the neuroganglion cell density. The histopathologic changes induced by galactose were manifested as outer hair cell loss and a decrease in neuroganglion cell density. Control animals had the least amount of hair cell loss and the greatest neuroganglion cell density of all three groups. Galactose-only animals demonstrated the most pronounced changes in both hair cell loss and neuroganglion cell degeneration; however, only changes of neuroganglion cell density in the basal turn were significant. The addition of an aldose reductase inhibitor provided inconclusive results in both hair cell determination and neuroganglion cell density; however, generally the inhibitor partially prevented the damage produced by galactose. These results suggest that a high-galactose diet can induce diabetic-like changes in the cochlea.

Aldehyde Reductase↗

PubMed1995

Immunohistochemical characterization of nitric oxide synthase activity in squamous cell carcinoma of the head and neck.

This study was designed to investigate the presence of nitric oxide in human squamous cell carcinoma of the head and neck. We localized the activity of nitric oxide synthase in these tumors through immunohistochemical analysis using antibodies to L-citrulline (a byproduct of nitric oxide synthase), to inducible nitric oxide synthase, and to constitutive nitric oxide synthase. We found presence of inducible enzyme in squamous cells throughout these tumors, with the highest intensity staining occurring directly around keratin pearls. Our findings suggest that inducible nitric oxide synthase activity is present in squamous cell carcinomas of the head and neck, leading us to conclude that inducible nitric oxide synthase may play a significant role in tumor growth.

Awards and Prizes↗

PubMed1995

Insulin-dependent diabetic microangiopathy in the inner ear.

Thickening of the basement membrane in capillaries is implicated in the microangiopathic complications of diabetes mellitus. This study was designed to evaluate microangiopathic changes of the inner ear associated with insulin-dependent diabetes mellitus (IDDM) and concurrent moderate-intensity noise exposure. Male Sprague-Dawley rats were injected with streptozotocin (65 mg/kg) to induce IDDM. Half of the control and diabetic animals were exposed to chronic noise of 95 dB over the 6-month study period. Photomicrographs of the capillaries in the stria vascularis were obtained by transmission electron microscopy, and basement-membrane thickness was measured with an image processing system. This study quantitatively demonstrates basement-membrane thickening consistent with diabetic microangiopathy in the inner ear of IDDM rats. Noise exposure did not significantly change basement-membrane thickness in either diabetic or control animals.

Animals↗

PubMed1994

The ototoxicity of 3,3'-iminodipropionitrile: functional and morphological evidence of cochlear damage.

Previous reports have suggested that IDPN may be ototoxic (Wolff et al., 1977; Crofton and Knight, 1991). The purpose of this research was to investigate the ototoxicity of IDPN using behavioral, physiological and morphological approaches. Three groups of adult rats were exposed to IDPN (0-400 mg/kg/day) for three consecutive days. In the first group, at 9-10 weeks post-exposure, thresholds for hearing of 5.3- and 38-kHz filtered clicks were measured electrophysiologically and brainstem auditory evoked responses (BAERs) were also recorded to a suprathreshold broadband click stimulus. A second set of animals was tested at 9 weeks for behavioral hearing thresholds (0.5- to 40-kHz tones) and at 11-12 weeks post-exposure for BAER thresholds (5- to 80-kHz filtered clicks). A third group of animals was exposed (as above), and killed at 12-14 weeks post-exposure for histological assessment. Kanamycin sulfate was used as a positive control for high-frequency selective hearing loss. Surface preparations of the organ of Corti were prepared in order to assess hair cells, and mid-modiolar sections of the cochlea were used to examine Rosenthal's canal and the stria vascularis. Functional data demonstrate a broad-spectrum hearing loss ranging from 0.5 kHz (30 dB deficit) to 80 kHz (40 dB deficit), as compared to a hearing deficit in kanamycin-exposed animals that was only apparent at frequencies greater than 5 kHz. Surface preparations revealed IDPN-induced hair cell loss in all turns of the organ of Corti, with a basal-to-apical gradient (more damage in the basal turns) at the lower dosages. At higher dosages there was complete destruction of the organ of Corti. There was also a dosage-related loss of spiral ganglion cells in all turns of the cochlea, again with a basal-to-apical gradient at the lower dosages. These data demonstrate that IDPN exposure in the rat results in extensive hearing loss and loss of neural structures in the cochlea.

Acoustic Stimulation↗

PubMed1994

Nitric oxide synthase is an active enzyme in the spiral ganglion cells of the rat cochlea.

Nitric oxide (NO) mediates the effects of the excitatory amino acids in the central nervous system. Excitatory amino acids, in particular L-glutamate, are thought to be the neurotransmitter(s) present at the cochlear hair cell-afferent nerve synapse. To our knowledge, no studies to date have documented the presence of NO in the cochlea nor attempted to elucidate the role of NO in hearing. Rat cochlea frozen sections were examined for the presence of nitric oxide synthase (NOS) by NADPH diaphorase histochemistry. Vibratome sections of rat cochlea were examined by immunocytochemistry with an antibody to citrulline, an indication of NOS activity. Spiral ganglion cells in the rat cochlea were positive by NADPH diaphorase histochemistry and by anti-citrulline immunocytochemistry. These results indicate that NOS is present and that the enzyme actively produces nitric oxide in the spiral ganglion cells of the rat cochlea. Given our current understanding of neurotransmission in the cochlea, it is reasonable to postulate that the actions of NO in cochlear neuronal tissue are similar to the actions of NO in the CNS and that NO acts as a neurotransmitter/neuromodulator in the cochlea. In addition, because NO has been implicated as a mediator of excitotoxicity in the CNS, NO may play a role in neurotoxicity in the cochlea.

Amino Acid Oxidoreductases↗

PubMed1994

Tracheal vascular response to hypertonic and hypotonic solutions.

One of the major roles of the upper respiratory mucosa is to humidify inspired air. This function requires the coordinated activity of respiratory epithelium and mucosal vasculature. It has been difficult to study this relationship in vivo. In the present study, we investigated the effects of osmolarity on the vessel diameter of mucosal vessels via a specially constructed chamber that allows direct visualization of the rat trachea microvasculature. With use of an anesthetized and instrumented rat preparation, the luminal surface of the dorsal wall of the trachea was superfused with physiological solutions at 37 degrees C. The osmolarities were varied by removing or adding NaCl or mannitol (200, 290, and 500 mosM). The mucosal vessels dilated when the airway surface was superfused with hypertonic solutions and constricted when superfused with hypotonic solution. The largest changes occurred in the arterioles (51 +/- 5.6 microns diam), which constricted by 10 +/- 2.18 microns (P = 0.0001) when exposed to a 200 mosM solution and dilated by 11 +/- 1.55 microns (P = 0.0001) when exposed to a 500 mosM NaCl-enriched solution. Smaller changes of similar pattern were seen in venules. The changes in vessel diameter were readily reversible upon replacement of the hypo- or hypertonic solutions by an isotonic solution. We conclude that increase or decrease of solution osmolarity on the epithelial surface of the trachea can regulate diameter of mucosal blood vessels.

Animals↗

PubMed1994

Nitric oxide in the rat vestibular system.

Nitric oxide is known to function as a neurotransmitter in the central nervous system. It is also known to be involved in the central nervous system excitatory amino acid neurotransmission cascade. Activation of excitatory amino acid receptors causes an influx of calcium, which activates nitric oxide synthase. The resulting increase in intracellular nitric oxide activates soluble guanylate cyclase, leading to a rise in cyclic guanosine monophosphate. The excitatory amino acids glutamate and aspartate are found in the vestibular system and have been postulated to function as vestibular system neurotransmitters. Although nitric oxide has been investigated as a neurotransmitter in other tissues, no published studies have examined the role of nitric oxide in the vestibular system. Neuronal NADPH-diaphorase has been characterized as a nitric oxide synthase. This enzyme catalyzes the conversion of L-arginine to L-citrulline, producing nitric oxide during the reaction. We used a histochemical stain characterized by Hope et al. (Proc Natl Acad Sci 1991;88:2811) as specific for neuronal nitric oxide synthase to localize the enzyme in the rat vestibular system. An immunocytochemical stain was used to examine rat inner ear tissue for the presence of the enzyme's end product, L-citrulline, thereby demonstrating nitric oxide synthase activity. Staining of vestibular ganglion sections showed nitric oxide synthase presence and activity in ganglion cells and nerve fibers. These results indicate the presence of active nitric oxide synthase in these tissues and suggest modulation of vestibular neurotransmission by nitric oxide.

Amino Acid Oxidoreductases↗

PubMed1993

Control of the mucosal microcirculation in the upper respiratory tract.

This study was designed to investigate the regulatory mechanisms of the mucosal microvascular network in the upper respiratory tract. Tracheal mucosal circulation was observed using a specially constructed chamber that allowed direct microscopic visualization of mucosal arterioles. Solutions of increasing hypertonicity (500 and 900 mOsm) applied to the tracheal epithelium resulted in increasing dilation of the underlying mucosal arterioles (p < 0.001). N(omega)-nitro-L-arginine methyl ester (L-NAME, 1 mmol/L), a specific inhibitor of nitric oxide synthesis, added to a hypertonic solution inhibited dilation of mucosal arterioles (p < 0.001). Addition of the substrate for nitric oxide synthesis, L-arginine (0.6 mmol/L) to the hypertonic solution containing L-NAME resulted in dilation of mucosal arterioles once again. These data demonstrate that nitric oxide is a crucial mediator in the response of mucosal arterioles to the hypertonic stimulus presented to the epithelial surface of the trachea. Further elucidation of the control of the mucosal microcirculation in the upper respiratory tract could be implemented in new treatment for pathologic processes of the upper respiratory tract such as mucosal congestion and edema.

Analysis of Variance↗

PubMed1993

Use of poly-l-aspartic acid to inhibit aminoglycoside cochlear ototoxicity.

Gentamicin is an extremely effective antibiotic against a wide variety of organisms. However, its use is limited by its nephrotoxic and ototoxic effects. Recent studies in rats have shown that poly-l-aspartic acid (PAA) effectively blocks the nephrotoxic effects of the aminoglycosides and does not decrease the antibiotic effectiveness of gentamicin against those organisms tested. A controlled test was undertaken to evaluate the effect of PAA on cochlear ototoxicity. Test solutions were administered to four groups of guinea pigs for 10 days. Group 1, the controls, received distilled water, group 2 received gentamicin, group 3 received PAA, and group 4 received gentamicin plus PAA. Auditory brainstem response thresholds at 20, 16, 8, and 4 kHz were obtained before therapy, after completion of the 10-day course, and 21 days following the completion of therapy. Two-dimensional diffusion assays in human serum were performed to evaluate the effect of PAA on the antimicrobial activity. Histologic evaluation of the cochleae was performed at the conclusion of the experiment. Threshold shifts following 10 days of therapy were not statistically significant in group 4 compared to controls, while the gentamicin group (group 2) was significantly different for all frequencies tested. At 21 days following therapy, group 4 (PAA + gentamicin) maintained significance in the higher frequencies studied. Antimicrobial studies demonstrated that PAA has no effect on the antimicrobial activity of gentamicin and has no antimicrobial effect against Bacillus subtilis when used alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Innervation of the endolymphatic sac.

Previous studies suggest that the endolymphatic sac plays an important role in the homeostasis of endolymph. Factors that influence blood flow in the sac may affect its function. This blood flow may be influenced by autonomic innervation; however, no such innervation has been demonstrated. The purpose of this study was to demonstrate catecholaminergic and cholinergic fibers on the endolymphatic sac. Endolymphatic sacs from Hartley guinea pigs were stained either immunocytochemically for tyrosine hydroxylase to reveal catecholaminergic fibers or histochemically for acetylcholinesterase to reveal cholinergic fibers. For tyrosine hydroxylase immunostaining, the endolymphatic sacs were treated with dilute hydrogen peroxide and then incubated in the primary antiserum. The tissue was further processed by the avidin-biotin immunoperoxidase method and reacted with diaminobenzidine. For acetylcholinesterase histochemistry, the tissue was processed by a modification of the direct thiocholine method. Light microscopy of the whole-mounted endolymphatic sacs revealed tyrosine hydroxylase-positive and acetylcholinesterase-positive fibers. Some of the acetylcholinesterase-positive fibers were clearly associated with vessels. This innervation, which has not been described previously, may significantly influence blood flow and function of the endolymphatic sac.

Acetylcholinesterase↗

PubMed1992

Cholinergic innervation of the guinea pig tympanic membrane.

While cholinergic nerve fibers of the parasympathetic system have been demonstrated in the middle ear mucosa, such innervation of the tympanic membrane has never been shown. Such fibers may prove important since the tympanic membrane may be one of the initial sites of effusion production, and since parasympathetic innervation is thought to be involved with middle ear effusion. To demonstrate cholinergic innervation, we have used modified direct thiocholine histochemical staining. Anesthetized Hartley guinea pigs were killed, and the tympanic bullae were removed intact, fixed in 4% paraformaldehyde, and then stained whole. Following staining, the tympanic membrane was dissected from each bulla and whole-mounted for light microscopy. Numerous acetylcholinesterase-positive fibers were observed on the tympanic membrane. Some fibers appeared to be vessel associated, although the majority did not. This suggests that these fibers may act on the mucosa or vasculature of the tympanic membrane and contribute to the pathogenesis of middle ear effusion.

Acetylcholinesterase↗

PubMed1992

Ciprofloxacin. Use as a topical otic preparation.

Most common topical otic preparations have been shown to cause sensorineural hearing loss and hair-cell damage in experimental animals. Ciprofloxacin is a relatively new fluoroquinolone with excellent activity against Pseudomonas and methicillin-resistant Staphylococcus aureus. Recent studies have shown oral ciprofloxacin to be effective in the treatment of chronic serous otitis media and malignant external otitis. However, this drug has never been used as a topical otic preparation. Thirty-five albino female guinea pigs were used to investigate the ototoxicity of topical ciprofloxacin hydrochloride. Bilateral transbullae drug delivery tubes were placed and auditory brain-stem response thresholds were recorded at 20, 16, 8, and 4 kHz before treatment and 21 days after the completion of treatment. Two groups of guinea pigs were used. In group 1 (positive controls), five guinea pigs had 0.1 mL of neomycin sulfate administered in one ear while the opposite (control) ear received 0.1 mL of 0.9% sodium chloride solution; in group 2, 30 guinea pigs received 0.75% ciprofloxacin ophthalmic solution and 0.9% sodium chloride solution in the control ear. All drugs were given twice a day for 7 consecutive days. All results were evaluated with paired, two-tailed t test and Hotelling's T2 test, and calculation of power was performed on all nonsignificant results. No significant ototoxic reaction was observed; small increases in hearing thresholds occurred at 4 (5.65 +/- 8.25 dB [mean +/- SD]) and 8 kHz (3.70 +/- 6.63 dB [mean +/- SD]) in the ciprofloxacin-treated ears; however, no significant hair-cell loss was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Topical↗

PubMed1992

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

The congenic spontaneous hypertensive/National Institutes of Health (Bethesda, Md)-corpulent rat (SHR/N-cp) is a model for non-insulin-dependent diabetes mellitus. A previous study in our laboratory found significant loss of outer hair cells (OHC) in diabetic rats at 5.0 months of age. Our present study was designed to further evaluate the effects of the diabetic state on the inner ear in 10.5-month-old rats. The following comparisons were made: diabetic vs euglycemic control animals; obese vs lean phenotypes; and sucrose vs starch as the source of dietary carbohydrate. Cochleas were removed, fixed, stained, mounted on slides, and analyzed for OHC loss. We found a significant OHC loss in the cochleas of all diabetic animals. No statistical difference was found when comparing obese and lean phenotypes. Increased OHC loss was observed in all sucrose-fed vs starch-fed diabetic animals, although this increase was not statistically significant. Compared with an earlier study, an increase in OHC loss was also noted in the 10.5-month-old lean SHR/N-cp animals. Our results indicate that there is a relationship between non-insulin-dependent diabetes mellitus and inner ear damage and suggest that OHC loss is related to hyperglycemia and a genetic predisposition for glucose intolerance.

Aging↗