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Biomedical subjects

D J Creel

Publications and source records attributed to D J Creel.

42 records · Page 3Linked to original sources
PubMedDate not supplied

Effects of aging on normal hearing loss and noise-induced threshold shift in albino and pigmented guinea pigs.

In a previous investigation into noise-induced hearing loss by comparing 2-month-old albino with pigmented guinea pigs, albinos displayed significantly greater shifts in cochlear microphonic (CM) threshold and less recovery than the pigmented animals 7 days after noise exposure. The present study compared the responses of 14-month-old albino and pigmented guinea pigs to the same noise parameters used previously. Thresholds for the first detectable elicitation of CM for three pure tones were recorded prior to, at 90 min and at 7 days after a 45-min exposure to 126 dB broadband noise. Before exposure to noise, thresholds for pigmented guinea pigs were 24 dB higher than those in the albinos. Following noise exposure, the pigmented animals showed less than half the amount of threshold shift displayed by the albinos. This change ws attributed to the higher pre-exposure thresholds in the pigmented guinea pigs. Converging lines of evidence suggest that cochlear pigmentation may have both protective and toxic influences on the inner ear.

Aging↗
PubMedDate not supplied

Comparative anatomy of melanin pigment in the stria vascularis. Evidence for a distinction between melanocytes and intermediate cells in the cat.

Although Corti in 1851 first described the presence of cochlear pigmentation in the stria vascularis (SV) of "very old" cats, modern studies have failed to find pigment consistently in the feline stria. While the variable presence of pigment in the feline SV would appear to contrast with this structure's uniform pigmentation in other mammalian species, variability in both the distribution and abundance of inner ear pigment has rarely been studied in any species. In the present study, the SV was examined light microscopically in sectioned material or whole-mounts from pigmented and albino animals of 5 species, including the cat, guinea pig, rabbit, ferret and mouse. In these species, the SV of each pigmented animal contained varying amounts of melanin pigment and none was found in the albino inner ear. Pigmented guinea pigs contained the most uniformly dense and least variable distribution of strial melanin, followed by the rabbit, mouse, ferret and cat. Several species also displayed more strial pigment apically and less basally. In cats, pigmented cells were principally located adjacent to the strial capillaries. Ultrastructural studies of the stria in pigmented cats revealed that these perivascular cells frequently contained an abundance of pigmented organelles and other structural features which allowed them to be distinguished from intermediate cells.

Animals↗
PubMedDate not supplied

Magnetic resonance imaging of the visual pathways in human albinos.

Neuroanatomical and electrophysiological studies of albino visual pathways have demonstrated that retinogeniculate axons arising from the temporal retina decussate abnormally in the optic chiasm to synapse in the contralateral lateral geniculate nucleus (LGN). Anomalies in the LGN secondarily disrupt normal geniculo-cortical and interhemispheric cortico-cortical (callosal) visual connections. It is not known whether retinogeniculate misrouting affects the size or configuration of the afferent visual pathways in human albinos. We used T1-weighted coronal and sagittal magnetic resonance imaging (MRI) to examine the prechiasmatic intracranial optic nerves, optic chiasm, and corpus callosum in 10 human albinos. In all subjects, these structures were normal in size and configuration. Despite the complex cascade of aberrant central neuronal connections, the human albino visual pathways and their interhemispheric connections appear normal in size and configuration when viewed with MRI.

Adolescent↗
PubMedDate not supplied

Hyperopic shift induced by high altitude after radial keratotomy.

BACKGROUND: The collagen fibrils embedded in the ground substance of the stromal lamellae provide the structural support for the cornea. When the stromal lamellae are cut in a radial keratotomy surgical procedure, the remaining uncut lamellae carry the tensile forces. METHODS: We studied two expert climbers who had bilateral radial keratotomy before participating in six climbs of extreme altitude, including Mount McKinley and above 7500 m (24,606 ft) on Mount Everest. RESULTS: Whenever either climber was exposed to altitudes greater than approximately 5000 m (16,405 ft) for more than a day, their refraction would become +3.00 D or more hyperopic and remain so al long as they were at or above this altitude. Visual acuity slowly returned to normal after descent. CONCLUSION: It appears that in the presence of significantly reduced atmospheric pressure and/or oxygen there is a greater effect of radial keratotomy in some patients, making the cornea more vulnerable to changes in shape. The cornea appears to respond by further flattening, exacerbating the intended surgical effect and producing a refractive shift toward hyperopia.

Adult↗
PubMedDate not supplied

Clofazimine-induced bull's-eye retinopathy.

Bull's-eye retinopathy has multiple associations. We report a case of bull's-eye retinopathy presumed to be secondary to clofazimine (Lamprene) treatment of a 30-year-old patient with acquired immunodeficiency syndrome (AIDS). Pretreatment baseline eye exam of this patient was normal except for bilateral cotton-wool spots. However, follow-up exam 5 months later revealed bilateral anterior pigmentary corneal deposits in a whorl pattern, a presumed infectious retinitis in the left eye, and bilateral annular macular pigmentary abnormalities. The patient was taken off clofazimine treatment, but died 1 month later. The authors suggest that patients being treated with clofazimine be examined for drug-related corneal and retinal lesions.

Acquired Immunodeficiency Syndrome↗