PubMed Health⌕ Search

Biomedical subjects

D B Webster

Publications and source records attributed to D B Webster.

At least 19 recordsLinked to original sources
PubMed1992

Degeneration followed by partial regeneration of the organ of Corti in deafness (dn/dn) mice.

The deafness mouse is a Mendelian recessive mutant which never hears and has no stimulus-related receptor or neural auditory responses. From birth through 12 days after birth (DAB), the organ of Corti develops normally as seen with light microscopy, except that the space of Nuel does not fully develop. The inner and outer hair cells are degenerating between 12 and 24 DAB and are gone by 45 DAB. As the hair cells degenerate, other cells of the organ of Corti become less recognizable, appear to collapse, and lose their identities as differentiated cells. By 45 DAB, from base to apex, the organ of Corti is composed of a low, roughly cuboidal epithelium with no distinguishing cell types; a hint of a tunnel of Corti remains at the apex. In the basal turn, the organ of Corti remains in this degenerated state through at least 460 DAB (senility for these mice). In the apical organ of Corti, considerable regeneration occurs between 45 and 90 DAB. By 90 DAB the apical turn of the organ of Corti has readily identifiable inner and outer pillar cells, inner and outer supporting cells, Hensen's cells, and Claudius' cells. A tunnel of Corti and space of Nuel are also present in the apex but there are no hair cells. Mechanisms are not known for either the degeneration or the regeneration.

Animals↗
PubMed1991

Neonatal conductive hearing loss does not compromise brainstem auditory function and structure in rhesus monkeys.

The effect of conductive hearing loss on the maturation of the auditory pathway was evaluated using the auditory brainstem response (ABR) in rhesus monkeys. Ten newborn rhesus monkeys were assigned to control (N = 4), unilateral hearing loss (N = 3), or bilateral hearing loss (N = 3) groups. Hearing loss was created by surgically excising a 3 mm section of the external auditory canal and suturing the canal. Auditory brainstem responses to click stimuli were recorded prior to and after the surgical procedure and bi-monthly or monthly for a 14 month follow-up period. Results showed that after surgery all ears developed an estimated 30-50 dB conductive hearing loss which was retained throughout the follow-up period. Contrary to expectations, the latencies of the ABR component waves decreased with age in all ears. When adjusted for hearing level, there were no differences between ears in maturation of the component waves of the ABR. These data suggest that, in primates, a conductive hearing loss does not affect the maturation of those aspects of the auditory pathway reflected in the ABR. Furthermore, the conductive losses were not accompanied by any discernible change in the neuronal sizes of brainstem auditory neurons or the volume of the cochlear nuclei.

Animals↗
PubMed1979

Aspects of planning and evaluation of children's dental care in Appalachia.

The dental public health literature contains almost no information on caries experience and treatment needs of Appalachian children, and little information concerning resource requirements for children's dental care programs in general. Data from three dental treatment programs in Appalachia are summarized for purposes of planning and evaluation of similar programs. Age specific caries and service experiences are presented, and evaluation criteria and planning considerations are discussed. Resource requirements, including time, cost and manpower are also presented, and special considerations for planning programs are discussed.

Adolescent↗
PubMed1979

The caries-preventive effect of amine fluorides and inorganic fluorides in a mouthrinse or dentifrice after 30 months of use.

The study groups using a dentifrice and mouthrinse both containing fluorides, a dentifrice containing stannous fluoride and a mouthrinse containing sodium fluoride, or a mouthrinse containing sodium fluoride with a placebo dentifrice had a 20.7% to 29.0% lower DMF increment than the control group after 30 months. These differences were significant. The study groups using a dentifrice containing amine fluorides and a placebo mouthrinse, a mouthrinse containing amine fluorides and a placebo dentifrice, or a dentifrice containing stannous fluoride and a placebo mouthrinse had a 13.6% to 22.4% lower DMF increment than the control group. These differences were not statistically significant. There was no significant difference in effectiveness against caries between the use of the organic or inorganic fluoride products.

Amines↗
PubMed1978

Anatomical consequences of CO2 laser surgery of the guinea pig ear.

A modified American Optical (Model 100) CO2 laser was used to produce lesions in the tympanic membranes, ossicles, and cochlear capsules of guinea pigs. Even with the lowest available intensities and durations (0.4 watts, 50 msec), there was damage to the inner ear. Although laser surgery of the ear can avoid mechanical trauma and bleeding as well as increase accuracy, the use of commercial lasers in ear surgery should be avoided until a proven unit is available.

Animals↗
PubMed1977

Neonatal sound deprivation affects brain stem auditory nuclei.

CBA/J mice deprived of airborne sound stimulation during postnatal development have smaller globular cells in the ventral cochlear nucleus and smaller neurons in the medial nucleus of the trapezoid body than do normal control mice. The sound deprivation in these mice is similar to that experienced by persons with pure congenital conductive hearing losses. Even more profound central neural changes were found in auditory nuclei in the brain stem of a congenitally sensorineural deaf human.

Acoustic Stimulation↗
PubMed1977

Effects of an amine fluoride mouthrinse and dentifrice on the gingival health and the extent of plaque of school children.

A study to test the efficacy of two amine fluoride products in reducing the extent of plaque and the degree of gingivitis was conducted with 6th-grade school children in Pensacola, Florida. The treatment regimens consisted of a daily supervised mouthrinse at school and the ad libitum home use of a dentifrice. Examinations were conducted at 12-week and 20-week intervals after the treatment had begun. There was no recognizable difference between the plaque and gingival reductions achieved with the use of the amine fluoride dentifrice or mouthrinse when compared either with their inorganic counterparts or with placebo treatment vehicles

Amines↗
PubMed1976

An evaluation of single and combined self-applied fluoride programs in schools.

1. The combined use of a twice-yearly, self-applied 2.2 percent phosphate fluoride prophylactic paste and a weekly 0.2 percent sodium fluoride mouthrinse resulted in a significantly lower caries prevalence at the same school after two years. 2. The use of a weekly 0.2 percent sodium fluoride mouthrinse alone resulted in a significantly lower caries prevalence among 11 year olds at the same school after two years. 3. The use of a twice-yearly 2.2 percent phosphate fluoride self-applied prophylactic paste did not result in a significant difference in caries prevalence at the same school after two years. 4. The combination of methods appeared to be more effective than either method used alone and the programs were more effective among nonwhites in this population with this type of analysis. 5. A study design which uses cross-sectional data to estimate incidence and to make prevalence comparisons at two different points in time can be useful when an evaluation of the effect of previously tested products is desired in school-based programs.

Child↗
PubMed1975

Auditory systems of Heteromyidae: functional morphology and evolution of the middle ear.

Middle ears (515) from 26 species of the rodent family Heteromyidae - genera Dipodomys, Microdipodops, Perognathus, and Liomys - were studied both grossly and histologically, for qualitative and quantitative comparisons. Middle ear modifications characteristic of each genus are qualitatively described. Quantitative comparisons are made among the 26 species in the study. Some correlations between middle ear size and other measurements are discussed. The middle ear is an acoustical transformer that for best efficiency must match the impedance of the cochlea to the impedance of the air in the external auditory meatus. It accomplishes this by a pressure increase and a velocity decrease through the combined effects of the lever and areal ratios; however, because the important consideration is a matching of two impedances rather than an absolute pressure increase, the pressure transformer ratio is a less informative measure of the middle ear's efficiency than is the impedance transform ratio. The impedance transformer mechanism is explained (from a morphological point of view), and equations are presented. Dipodomys, Microdipodops, and Perognathus have a theoretical transmission (at the resonant frequency) of 94-100% of the incident acoustical energy; Liomys, 78-80%. The areal ratio of stapes footplate to 2/3 tympanic membrane is remarkably constant among the species, varying only from 0.04 to 0.07: in Dipodomys and Microdipodops this small ratio is due to the very large tympanic membrane; in Perognathus and Liomys it is due to the extremely small stapes footplate. The lever ratio of incus to malleus varies from 0.28 to 0.33 in Dipodpmys and Microdipodops, from 0.37 to 0.46 in Perognathus, and from 0.55 to 0.60 in Liomys. In addition, the middle ear volumes and the morphology of tympanic membrane, ossicles, ligaments, and muscles, all combine to minimize both mass and stiffness. All these data suggest middle ear mechanisms which are very efficient over a broad frequency range. The middle ear modifications found in heteromyids are adaptive in predator avoidance, especially in areas of little natural cover; nevertheless, contrary to expectations, there is no firm relationship between habitat and the extent of these modifications in the 26 species. However, environment did apparently plan an important role in the evolution of the family, and this is discussed.

Acoustics↗
PubMed1975

Auditory systems of Heteromyidae: postnatal development of the ear of Dipodomys merriami.

Serial histological sections of kangaroo rats of postnatal ages 0-, 3-, 7-, 10-, and 14-days were prepared and studied. At birth the middle ear is mostly filled with mesenchyme and small in size, having only a small hypotympanum and a very small epitympanic recess. During the first postnatal two weeks, much of the hypertrophy found in the adult middle ear develops. Because an entotympanic element is nev er formed, the previously called entotympanic chamber is here renamed the hypotympanum. The epitympanic recess greatly expands to form what has been called the dorsal (or anterior) mastoid sinus. Since this chamber has no relation to the mastoid, it is here renamed the epitympanum. Posteriorly, the previously called posterior mastoid sinus develops from the growth of the hypotympanum into and beyond the region of the posterior and horizontal semicircular canals. In development and adult position it is comparable to the primate antrum and so is here renamed the antrum. At birth the organ of Corti is very immature but its major cell types can be identified. During the first two weeks of development the following events occur: (1) the vas spirale disappears, (2) the inner spiral sulcus cells atrophy, (3) the hair cells and supporting cells mature, (4) the cells of Hensen differentiate with their apical processes elevating the reticular lamina, (5) the innermost cell of Claudius migrates under and supports the Hensen's cells, and (6) the hyaline mass of the zona pectinata of the basilar membrane loses its connective tissue cells and expands in size. The developmental events support the previous description and identification of Hensen's and Claudius' cells.

Age Factors↗
PubMed1975

Projections of the trapezoid body and the superior olivary complex of the Kangaroo rat (Dipodomys merriami).

Glass micropipettes filled with 2 M sodium cyanide were used to physiologically locate and iontophoretically damage the nucleus of the trapezoid body (NTB), the medial superior olive (MSO), and the lateral superior olive (LSO). Mechanical lesions were made in the trapezoid body as it leaves the cochlear nuclei. After a 3- to 10-day survival time the projections and terminal degeneration were traced with the Fink-Heimer and Nauta-Gygax stains. The ventral cochlear nucleus (VCN) projects via the trapezoid body to ipsilateral LSO, ipsilateral preolivary nuclei, ipsilateral lateral and a contralateral medial dendritic fields of MSO, and contralateral NTB; there is also a small ipsilateral projection to the ventral nucleus of the lateral lemniscus (VNLL) and the central nucleus of the inferior colliculus (CNIC). Some trapezoid body fibers ascend via the contralateral lateral lemniscus to VNLL, DNLL (dorsal nucleus of the lateral lemniscus), and CNIC. There is no projection from the ventral cochlear nucleus to the ipsilateral NTB and contralateral preolivary nuclei. All portions of NTB project ipsilaterally to LSO (ventral NTB to dorsomedial LSO, dorsal NTB to ventral LSO) and to the retro-olivary nucleus. In two animals with NTB lesions there is also degeneration in the ventromedial portion of the ipsilateral facial nucleus. NTB projects contralaterally by way of the stria of Monakow to the pyramidal and molecular cell layers of the dorsal cochlear nucleus (DCN). The NTB does not project ipsilaterally to MSO, preolivary nuclei, VNLL, DNLL and CNIC. Contralaterally there are no projections to any of the nuclei of the auditory pathway except the DCN. Most MSO projections are ipsilateral. The densest goes by way of the lateral lemniscus to the lateral aspect of the ipsilateral CNIC, terminating throughout its dorsoventral axis. MSO also projects bilaterally to the pyramidal and molecular cell layers of dorsal cochlear nucleus (DCN), and ipsilaterally to the ventral portion of the motor nucleus of V and to the facial nucleus. MSO does not project ipsilaterally to the LSO, NTB, preolivary, VCN and retro-olivary nuclei. On the contralateral side, all structures except the DCN are free of projection patterns from axons originating in the MSO. LSO projects bilaterally to the central and ventral portions of CNIC and to the nuclei of the lateral lemnisci, and ipsilaterally to the large and small spherical cell areas of anterior ventral cochlear nucleus (AVCN) and to all portions of DCN. The LSO does not project ipsilaterally to the NTB, MSO, preolivary and retro-olivary nuclei. On the side opposite, this nucleus does not project to NTB, MSO, retro-olive, VCN, preolivary and LSO. For all lesions regardless of the site, there is no degeneration found rostral to the CNIC. The medial geniculate body or other structures in the diencephalon or cortex are free of any fields of terminal degeneration.

Animals↗
PubMed1975

The effects of cosmic particle radiation on pocket mice aboard Apollo XVII: X. Results of ear examination.

In the five pocket mice flown on Apollo XVII, no evidence was found that the inner ear had been damaged, though poor fixation precluded detailed study. On the other hand, the middle ear cavity was involved in all the mice, hemorrhage having occurrred in response to excursions in pressure within the canister that housed the mice during their flight. The same occurred in flight control mice which had been subjected to pressure excursions of much the same magnitude. A greater degree of exudation into air cells and greater leukotaxis were noted in the flight animals than in the control animals. There was no increase in leukocyte population along the paths of the 23 cosmic ray particles registered in the subscalp dosimeters that traversed the middle ear cavities of the flight mice. The increased exudation and the greater response by leukocytes in the flight mice may have been causally related to the lesions found in their olfactory mucosa but there were no data in support of this possibility.

Animals↗
PubMedDate not supplied

Effects of neonatal conductive hearing loss on brain stem auditory nuclei.

Both postnatal auditory deprivation and experimentally produced conductive hearing losses in mice result in incomplete maturation of most brain stem auditory neurons. The affected groups are: octopus cell, globular cell, small spherical cell, and large spherical cell groups in ventral cochlear nuclei; and the lateral superior olive and medial nucleus of the trapezoid body of the superior olivary complex. When 45 days of auditory deprivation are followed by 45 days of normal acoustic stimulation, there is incomplete maturation of neurons in: multipolar cell, globular cell, small spherical cell, and large spherical cell groups in ventral cochlear nuclei; lateral superior olive and medial nucleus of trapezoid body in superior olivary complex; and central nucleus of inferior colliculus. A critical period exists when adequate sound stimulation is needed for full development of these neurons.

Acoustic Stimulation↗
PubMedDate not supplied

Cochlear nerve projections following organ of corti destruction.

Experimental organ of Corti destruction results in (1) secondary loss of all type I spiral ganglion neurons, (2) development of type III spiral ganglion neurons, (3) degeneration of most cochlear nerve myelinated fibers, and (4) terminal degeneration in the ventral and dorsal cochlear nuclei. The first signs of degenerative changes occur by eight days after organ of Corti destruction and degeneration debris remains until 28 weeks after destruction.

Animals↗