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Biomedical subjects

C G Wright

Publications and source records attributed to C G Wright.

At least 37 records · Page 2Linked to original sources
PubMed1993

Population growth of Dermatophagoides farinae Hughes (Acari: Epidermoptidae) suppressed by methoprene and hydroprene.

Insect growth regulators are synthetic chemicals that mimic the function of hormones that occur naturally in arthropods. Two such insect growth regulators, methoprene and hydroprene, were tested to determine effects on growth of laboratory populations of the American house dust mite, Dermatophagoides farinae Hughes. Adults and immature mites were treated with four concentrations of each chemical in contact and diet-incorporation bioassays. Data were collected after 30 and 90 d of exposure to the treatments. Both compounds significantly suppressed population growth when compared with acetone controls at concentrations of > or = 5%. Methoprene was more effective than hydroprene in diet-incorporation bioassays and was slightly more effective for the first 30 d of the contact assays. A second set of contact and diet-incorporation assays was done using one concentration (7.5%) of methoprene and hydroprene to determine the effect of these compounds on population dynamics of D. farinae. In this experiment, population numbers were evaluated at weekly intervals for 13 wk. The average number of mites in the untreated control population increased by more than 10 times the original inoculum during the experiment while the number of mites in the treated containers did not increase significantly. This trend was similar for both contact and diet-incorporation bioassays although the average number of mites per container was significantly higher when the treatments were incorporated in the house dust mite diet than when applied directly to the substrate.

Animals↗
PubMed1993

Ototoxicity of topical agents.

Topical otic preparations are commonly prescribed by otolaryngologists--head and neck surgeons. It is well documented in the literature that some agents in these preparations are ototoxic when applied to the middle ear in experimental animals, although the occurrence of ototoxicity in the clinical setting is controversial. This article discusses topical otic preparations currently available as well as various other agents. The clinician should prescribe these preparations with close surveillance for potential ototoxicity.

Administration, Topical↗
PubMed1993

Modified occipital approach to the endolymphatic sac and cochlear aqueduct of the guinea pig.

Obliteration of the endolymphatic sac reliably results in endolymphatic hydrops in some animal species. While this procedure is frequently utilized in the study of experimental Meniere's disease, additional information regarding inner ear fluid hydrodynamics can be obtained by obstructing the cochlear aqueduct to eliminate the influence of the cerebrospinal fluid on the perilymphatic compartment of the inner ear. This report describes a modified extradural occipital approach for surgical obliteration of the endolymphatic sac and obstruction of the cochlear aqueduct in the guinea pig. The extradural approach allows direct visualization of the cochlear aqueduct without manipulation or retraction of the dura, sigmoid sinus, or cerebellum. For experimental studies, which require obliteration of both the endolymphatic sac and cochlear aqueduct, this approach provides improved reliability with reduced morbidity and mortality.

Animals↗
PubMed1992

Alterations of inner ear morphology in experimental hypercholesterolemia.

Previous clinical and experimental studies have indicated that auditory function may be compromised by hypercholesterolemia. In this investigation, inner ear tissue from chinchillas maintained on a cholesterol-supplemented diet for 3 months was examined for morphological alterations which might underlie the physiological changes observed with this condition in earlier studies. Ultrastructural analysis of cochleas from 16 hypercholesterolemic chinchillas revealed alterations in both the stria vascularis and outer hair cells. Strial marginal cells throughout the cochlea and outer hair cells of the apical turn, contained electron-lucent patches of an amorphous material. These patches had the morphological characteristics and histochemical properties of glycogen. Mild extracellular edema and increased numbers of lysosomes were also noted in the stria vascularis of experimental animals. These alterations suggest that chronic hypercholesterolemia metabolically stresses inner ear tissue. It is hypothesized that such changes could increase susceptibility of the cochlea to ototraumatic agents.

Animals↗
PubMed1992

Hyperpigmentation of chinchilla stria vascularis following acoustic trauma.

This report describes morphological alterations of the chinchilla stria vascularis seen 30 days after exposure to impulse noise. The observed changes included a dramatic increase in strial melanin content which occurred in 7 of 36 animals exposed to electronically synthesized impluses presented in various temporal patterns at either 135 or 150 dB peak SPL. In these animals, densely pigmented areas of stria 1.5 to 3 mm in length were found in the basal cochlear turn. Light and electron microscopic study revealed that these areas contained large numbers of melanin granules situated primarily in pale-staining cells of the middle layer of the stria. Unlike the pigment granules present in normal chinchilla stria, the melanosomes found in the noise-exposed material clearly showed ultrastructural features characteristic of eumelanin. Melanin granules were also observed in marginal and basal cells of the noise-exposed stria. In some cases, pigment granules which had apparently been expelled from the marginal cells were present in the endolymphatic space beneath Reissner's membrane and on the strial surface. These findings support the view that the melanin-bearing cells of the inner ear are capable of markedly increased activity in response to stressful conditions.

Animals↗
PubMed1992

Incidence of otitis media in vitamin A-deficient guinea pigs.

After observing an association between vitamin A deficiency and otitis media among children in Micronesia, we sought to develop an animal model for vitamin A-deficiency-induced otitis media. Thirty juvenile guinea pigs were screened for absence for otitis and then divided into two groups. The experimental group was placed on a vitamin A-free diet, whereas control animals were fed a standard formula. The animals were followed by means of otologic examination and serum retinol determinations. When experimental animals demonstrated vitamin A deficiency, they were killed along with one control and temporal bones were harvested and prepared for histologic examination. None of the 15 controls demonstrated middle ear abnormalities. In the experimental group, 77% of temporal bones showed middle ear pathology consisting of either of subepithelial edema (27%) or frank otitis media (50%). These results indicate that the guinea pig is a suitable species for study of otitis media in association with vitamin A deficiency. We postulate that eustachian tube dysfunction is the primary mechanism for inducing middle ear inflammation in this animal model.

Animals↗
PubMed1991

Trapping efficiency of selected adsorbents for various airborne pesticides.

A study was conducted to compare the efficiency of five adsorbents used by government and private laboratories to collect airborne pesticides. Six pesticides, acephate, chlordane, chlorpyrifos, diazinon, heptachlor, and propoxur, were vaporized in a closed system and collected on each of the adsorbents, Chromosorb 102, ORBO 42, ORBO 44 (chlordane and heptachlor only), polyurethane foam (PUF) or Tenax GC, by drawing 250 L of air through the adsorbent. There were no differences in collection efficiency of the five pesticides on Chromosorb 102, ORBO's 42/44, and PUF. The efficiency with Tenax was somewhat less with several of the pesticides.

Adsorption↗
PubMed1991

Tympanic membrane microstructure in experimental cholesteatoma.

This study assessed changes in tympanic membrane microstructure associated with cholesteatoma development following middle ear application of 50% propylene glycol in chinchillas. Although the epidermal layer of the tympanic membrane (TM) was destroyed immediately after propylene glycol application, the epidermal basal lamina remained intact and appeared to serve as a substrate for regrowth of epidermis over the TM. During the initial phase of epidermal repair (4 to 7 days after propylene glycol administration), pseudopodial processes from the epidermal cells occasionally penetrated the basal lamina; however, no migration of epidermis into the lamina propria occurred at that time. The basal lamina remained largely intact until about 2 weeks, when it became fragmented in some areas, so that sizable gaps appeared. Hyperplastic epidermal cells then migrated through the gaps into the rapidly proliferating connective tissue of the lamina propria. At 2 to 4 weeks, degenerative changes were observed in portions of the fibrous layer, which underwent phagocytosis by foreign body giant cells. This process created defects in the fibrous layer which permitted invasion of epidermis to the medial portion of the lamina propria. The epidermis subsequently reached the medial side of the TM in areas where there was incomplete repair of the mucosal layer.

Animals↗
PubMed1991

Ototoxicity of an ototopic preparation--experimental results and clinical facts.

The ototoxicity of "Cortisporin Otic Suspension" containing 3.5 ml neomycin base, 10,000 units/ml polymyxin B was studied using the baboon (papio ursinus) as an experimental animal. Inner and outer hair cell loss occurred in all cochleas of the ears which received cortisporin. Most lesions were confined to the basal turn of the organ of Corti. Separate evaluation of polymyxin B and neomycin at the same concentration as in cortisporin showed that polymyxin B produced greater cochlear damage. The results of this study and clinical reports of sensorineural hearing loss due to commercially available ear drops indicate that ototopical preparations must be used with caution in clinical situations in which they may reach the middle ear.

Animals↗
PubMed1990

Effect of topical fosfomycin on polymyxin B ototoxicity.

Fosfomycin is an antibiotic that has been found to reduce the ototoxicity of aminoglycoside antibiotics and cisplatin when systemically coadministered. Polymyxin B, an antibiotic frequently used in ototopical preparations, has been shown to be ototoxic in experimental studies. To investigate the effect of fosfomycin on polymyxin B ototoxicity, topical administration of the two agents into the middle ear cavity was performed. Two groups of chinchillas were used. One group received applications of polymyxin B alone, and the second group received polymyxin B combined with fosfomycin. It was found that application of polymyxin B produces severe damage to the cochlea. However, when polymyxin B was given in combination with fosfomycin, cochlear damage was dramatically reduced. It is likely that in clinical use, a combination of polymyxin B and fosfomycin would demonstrate reduced risk of ototoxicity.

Administration, Topical↗
PubMed1990

Effects of five insect growth regulators on laboratory populations of the North American house-dust mite, Dermatophagoides farinae.

The potential of insect growth regulators (methoprene, hydroprene, fenoxycarb, diflubenzuron and triflumuron) to control populations of the North American house-dust mite Dermatophagoides farinae (Hughes) was assessed in laboratory bioassays. Methoprene was most effective at suppressing population growth, especially at concentrations of 1.0% (10,000 ppm) and 5.0% (5000 ppm) active ingredient. Hydroprene, structurally related to methoprene, also suppressed house-dust mite populations but not as consistently as methoprene. Fenoxycarb may be effective at controlling house-dust mites but at greater concentrations than were tested. Diflubenzuron and triflumuron, two chitin-synthesis inhibitors, failed to suppress mite numbers and may, in fact, stimulate reproduction in some cases. Almost all concentration of the insect growth regulators were shown to be ineffective when assayed 90 days after treatment.

Animals↗
PubMed1989

The ototoxicity of ceftazidime in the chinchilla middle ear.

Ceftazidime (Tazicef) is a broad-spectrum cephalosporin antibiotic that may be useful as a topical agent in the treatment of otorrhea. To test the potential ototoxicity of the drug, 0.5 mL of a 10% solution of ceftazidime was introduced into the bullae of 22 chinchillas. The organ of Corti was normal in 20 temporal bones examined at 1 week after administration of the ceftazidime solution. Only 2 of 24 temporal bones examined after 4 weeks showed minor outer hair cell loss of the basal turn of the organ of Corti. Focal hemorrhage and occasional serous effusions were found in the middle ears of all animals after 1 week; these findings had mostly cleared after 4 weeks. Our results indicate that ceftazidime causes reversible middle ear inflammation, and may have some minor ototoxic potential under these experimental conditions.

Administration, Topical↗