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Biomedical subjects

C Zinn

Publications and source records attributed to C Zinn.

At least 19 recordsLinked to original sources
PubMed2005

Development of a psychometrically valid and reliable sports nutrition knowledge questionnaire.

The present range of sports nutrition knowledge questionnaires have inadequate psychometric validation, and few are up to date in a rapidly changing discipline. The purpose of this study was to design a sports nutrition questionnaire that satisfied acceptable psychometric criteria of validity (content and construct) and reliability (test-retest). The questionnaire was designed by an expert panel of six sports dietitians and distributed to five groups, selected for their expected variation in sports nutrition knowledge. Dietitians, university business staff and nutrition students received questionnaires via e-mail. The response rates obtained were 21.3% (n = 49), 34.4% (n = 33), and 72.0% (n = 18), respectively. University business and fitness students completed questionnaires during class time. Response rates were 52.3% (n = 23) and 75.4% (n = 49), respectively. The questionnaire was administered a second time to the business staff and the dietitians to assess test-retest reliability. Two methods were used: 1, Pearson's product-moment correlation; and 2, a percentage calculation of questions answered in an identical manner on both test occasions. Reliability was acceptable with Method 1 yielding acceptable values (r = 0.74-0.93), aside from the fluid sub-category (r = 0.52). Method 2 showed good test-retest concordance with 81.2% duplication of responses of all questions. Construct validity was high, as indicated by significant mean knowledge score differences between the groups (p = 0.0001). Dietitians and nutrition students achieved significantly greater mean scores than the remaining groups. The findings of this study indicate that the questionnaire is suitably valid and reliable to be used in research and practice to determine sports nutrition knowledge.

Dietetics↗
PubMed2000

Evidence for active, nonlinear, negative feedback in the vibration response of the apical region of the in-vivo guinea-pig cochlea.

The transverse vibration response of the organ of Corti near the apical end of the guinea-pig cochlea was measured in vivo. For cochleae in good physiological condition, as ascertained with threshold compound action potentials and the endocochlear potential, increasing amounts of attenuation and phase lag were found as the intensity was decreased below 80 dB SPL. These nonlinear phenomena disappeared post mortem. The data suggest that an active, nonlinear damping mechanism exists at low intensities at the apex of the cochlea. The phase nonlinearity, evident at all frequencies except at the best frequency (BF), was limited to a total phase change of 0.25 cycles, implying negative feedback of electromechanical force from the outer hair cells into a compliant organ of Corti. The amplitude nonlinearity was largest above BF, possibly due to interaction with a second vibration mode. The high-frequency flank of the amplitude response curve was shifted to lower frequencies by as much as 0.6 octave (oct) for a 50-dB reduction of sound intensity; the reduction of BF was 0.3 oct, but there was no change of relative bandwidth (Q(10 dB)). Detailed frequency responses measured at 60 dB SPL were consistent with non-dispersive, travelling-wave motion: travel time to the place of BF (400 Hz at 60 dB SPL) was 2.9 ms, Q(10 dB) was 1.0; standing-wave motion occurred above 600 Hz. Based on comparison with neural and mechanical data from the base of the cochlea, amplitudes at the apex appear to be sufficient to yield behavioural thresholds. It is concluded that active negative feedback may be a hallmark of the entire cochlea at low stimulus frequencies and that, in contrast to the base, the apex does not require active amplification.

Acoustic Stimulation↗
PubMed2000

Thyroid hormone deficiency before the onset of hearing causes irreversible damage to peripheral and central auditory systems.

Both a genetic or acquired neonatal thyroid hormone (TH) deficiency may result in a profound mental disability that is often accompanied by deafness. The existence of various TH-sensitive periods during inner ear development and general success of delayed, corrective TH treatment was investigated by treating pregnant and lactating rats with the goitrogen methimazole (MMI). We observed that for the establishment of normal hearing ability, maternal TH, before fetal thyroid gland function on estrus days 17-18, is obviously not required. Within a crucial time between the onset of fetal thyroid gland function and the onset of hearing at postnatal day 12 (P12), any postponement in the rise of TH-plasma levels, as can be brought about by treating lactating mothers with MMI, leads to permanent hearing defects of the adult offspring. The severity of hearing defects that were measured in 3- to 9-mo-old offspring could be increased with each additional day of TH deficiency during this critical period. Unexpectedly, the active cochlear process, assayed by distortion product otoacoustic emissions (DPOAE) measurements, and speed of auditory brain stem responses, which both until now were not thought to be controlled by TH, proved to be TH-dependent processes that were damaged by a delay of TH supply within this critical time. In contrast, no significant differences in the gross morphology and innervation of the organ of Corti or myelin gene expression in the auditory system, detected as myelin basic protein (MBP) and proteolipid protein (PLP) mRNA using Northern blot approach, were observed when TH supply was delayed for few days. These classical TH-dependent processes, however, were damaged when TH supply was delayed for several weeks. These surprising results may suggest the existence of different TH-dependent processes in the auditory system: those that respond to corrective TH supply (e.g., innervation and morphogenesis of the organ of Corti) and those that do not, but require T3 activity during a very tight time window (e.g. , active cochlear process, central processes).

Animals↗
PubMed1999

Gene disruption of p27(Kip1) allows cell proliferation in the postnatal and adult organ of corti.

Hearing loss is most often the result of hair-cell degeneration due to genetic abnormalities or ototoxic and traumatic insults. In the postembryonic and adult mammalian auditory sensory epithelium, the organ of Corti, no hair-cell regeneration has ever been observed. However, nonmammalian hair-cell epithelia are capable of regenerating sensory hair cells as a consequence of nonsensory supporting-cell proliferation. The supporting cells of the organ of Corti are highly specialized, terminally differentiated cell types that apparently are incapable of proliferation. At the molecular level terminally differentiated cells have been shown to express high levels of cell-cycle inhibitors, in particular, cyclin-dependent kinase inhibitors [Parker, S. B., et al. (1995) Science 267, 1024-1027], which are thought to be responsible for preventing these cells from reentering the cell cycle. Here we report that the cyclin-dependent kinase inhibitor p27(Kip1) is selectively expressed in the supporting-cell population of the organ of Corti. Effects of p27(Kip1)-gene disruption include ongoing cell proliferation in postnatal and adult mouse organ of Corti at time points well after mitosis normally has ceased during embryonic development. This suggests that release from p27(Kip1)-induced cell-cycle arrest is sufficient to allow supporting-cell proliferation to occur. This finding may provide an important pathway for inducing hair-cell regeneration in the mammalian hearing organ.

Acoustic Stimulation↗
PubMed1997

Development of a narrow water-immersion objective for laserinterferometric and electrophysiological applications in cell biology.

Laserinterferometric studies of the micromechanical properties of the organ of Corti using isolated temporal bone preparations are well established. However, there are relatively few measurements under in vivo conditions in the apical region of the cochlea because of its inaccessibility with commonly used techniques. Recently, optical-design programs have become affordable and powerful, so that the development of an optimized optical system is within the budget of physiologists and biophysicists. We describe here the development of a long-range water-immersion objective. To circumvent anatomical constraints, it has a narrow conical tip of taper 22 degrees and diameter 2.4 mm. It is a bright-field reflected-light illumination, achromatic objective with magnification of 25x/infinity, a working distance of 2.180 mm and a numerical aperture of 0.45. Chromatic errors are corrected at 546.1 and 632.8 nm, with emphasis on the latter wavelength which is used by the laser interferometer. The field curvature is relatively flat and a diffraction limitation (Strehl ratio better than 0.8) can be obtained in a field of 0.4 mm diameter. Using this objective, sound-induced vibrations of hair cells and Hensen cells could be recorded without placing a reflector on the target area. In addition, this objective was found to be diffraction-limited in the near infra-red (750-830 nm), with a slightly different working distance (2.186 mm), making it suitable for patch-clamp experiments using infra-red, differential interference contrast.

Animals↗