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Biomedical subjects

J C Saunders

Publications and source records attributed to J C Saunders.

At least 19 recordsLinked to original sources
PubMed1992

Middle-ear development: II. Morphometric changes in the conducting apparatus of the chick.

The ontogeny of various middle-ear structures was examined in 11 groups of chicks between 10 days embryonic and adult. Measurements of the tympanic membrane surface area and height, columella length, and that of the columella footplate, annular ligament, and oval window area were obtained using video micrographs and computer digitization techniques. The oval window matures first at 53 days post-hatching, whereas the columella achieves adult size at 74 days. The tympanic membrane surface area is the last middle-ear variable studied to reach adult size (79 days post-hatch). The columella increases its length from 0.63 mm (10 days embryonic) to 2.73 mm in the adult. The tympanic membrane area expands by 280% whereas the columellar footplate area increases by 11x. As a result, the pressure amplification of the middle ear due to the tympanic membrane/columellar footplate area ratio improves by over 400%. These data further contribute to our understanding of the functional development of the middle ear.

Animals↗
PubMed1992

The structural and functional aspects of hair cell regeneration in the chick as a result of exposure to intense sound.

This paper summarizes the structural and functional damage caused by intense sound exposure in neonatal chicks. Scanning electron microscopy has been used to follow the structural changes to the papilla and their subsequent repair. Pure-tone exposures produced a localized lesion consisting of tectorial membrane destruction, changes in surface organization of the papilla, and hair cell loss. The papilla underwent significant repair following the exposure and new hair cells could be identified on the sensory surface after 4 days of recovery. In addition, various evoked-potential methods provided an objective assessment of auditory function and demonstrated that the peripheral ear was severely impaired by overstimulation. Auditory function returned to near normal levels within 3 days postexposure. The inescapable conclusion from these observations was that hair cell regeneration had little to do with the functional recovery observed during the first 3 days. Tectorial membrane regeneration and the restoration of cochlear micromechanics were combined to form a hypothesis to account for the restoration of auditory function.

Acoustic Stimulation↗
PubMed1992

Middle ear development. I: Extra-stapedius response in the neonatal chick.

A laser interferometry system was used to study the ontogeny of tympanic membrane mechanical responses to sound as measured at the tip of the extra-stapedius (ES) in chicks. The ES velocity and phase responses in the frequency range between 0.2 and 10.0 kHz were measured in animals ranging from 3 days of age to adult. The slope of the low frequency response remained constant with age while the ES low frequency sensitivity increased by 11 dB. The sensitivity improvement indicated an increase in low frequency middle-ear admittance. However, there was no consistent developmental improvement in high frequency ES sensitivity. Comparisons between the growth of low frequency ES velocity, the development of admittance magnitude, and evoked potential threshold sensitivity developmental data indicated no clear relation between these measures.

Acoustic Stimulation↗
PubMed1992

Stiffness of hair bundles in the chick cochlea.

The stiffness of hair bundles from isolated chick cochlear hair cells was measured in tissue culture medium. A water jet was used to deflect fiberglass fibers, quartz fibers, and hair bundles of isolated hair cells. A voltage-displacement curve was generated for a water jet ramp stimulus applied to miniature fiberglass and quartz fibers. Fiber displacements were measured using video image subtraction techniques. A force-voltage calibration curve was then derived for the fibers by modelling them as cantilever beams subjected to point forces at the tips. A voltage-displacement curve was then generated for isolated hair cell stereociliary bundles using the same procedure as for the fibers. A corresponding force-displacement curve was derived for isolated hair cells under water jet stimulation by correlating maximum ramp voltage from the hair cell's voltage-displacement curve to a corresponding force applied to a fiber from the fiberglass fiber calibration curve. The stiffness of the hair bundle, which is the slope of the hair cell's force-displacement curve, was then calculated using Hooke's law, assuming the force was distributed along the entire length of the hair bundle. The mean stiffness value was 5.04 +/- 2.68 x 10(-4) N/m for 14 hair cells, and was in close agreement with previously reported stiffness values of several investigators utilizing different animal models and procedures.

Animals↗
PubMed1992

Middle ear development. III: Morphometric changes in the conducting apparatus of the Mongolian gerbil.

Middle-ear structural ontogeny was examined in 12 age groups of Mongolian gerbils between 2 and 42 days after birth. Measurements of tympanic membrane surface area; depth of the tympanic membrane cone; the lengths of the malleus and incus long processes; and stapes footplate, annular space, and oval window areas were obtained using video micrographs and computer digitization techniques. The incus long process matured first at 3.5 days after birth, while the pars flaccida surface area was the last middle-ear variable studied to reach adult size (26 days after birth). The incus long process increased its length by 30% from 0.5 mm to 0.65 mm. The malleus long process, however, demonstrated much more relative growth (47%). Pars tensa area expanded from 6.35 mm2 at two days after birth to its adult size of 16.9 mm2 and the stapes footplate expanded by 50%. The developmental changes observed in middle-ear anatomy are then discussed with regard to their contribution to the functional maturation of both the middle ear and more central auditory function.

Animals↗
PubMed1992

Threshold shift, hair cell loss, and hair bundle stiffness following exposure to 120 and 125 dB pure tones in the neonatal chick.

One-day old chicks were exposed to one of two pure tone stimuli (0.9 kHz at 120 or 125 dB SPL) for 48 h. Three major results arose from a variety of tests that assessed the structural and functional consequences of the exposure on the peripheral auditory system at either 0 days or 12 to 15 days recovery. First, brainstem response data showed that the 120 and 125 dB groups had maximum evoked potential threshold shifts of 57 and 71 dB immediately after removal from the sound. Fifteen days post-exposure, the thresholds in the 120 dB group returned to near-normal levels, while in the 125 dB group, recovery was within 19 dB of control thresholds. Second, scanning electron microscopic measurements of hair cell density within the lesion showed that at 0 days recovery, the 120 and 125 dB groups had a 30% and 59% short hair cell loss, respectively, but by 15 days no differences could be identified between the exposed and control animals, regardless of exposure level. Finally, at 0 days of recovery, micromechanical stimulation data did not reveal any significant difference in stiffness between the control and surviving hair cells in the lesion area. Although the more intense exposure induced greater structural and functional damage in the chick cochlea, the birds retained or even enhanced their ability to replace lost hair cells and had partial hearing recovery by 15 days post-exposure.

Animals↗
PubMed1991

The structural and functional consequences of acoustic injury in the cochlea and peripheral auditory system: a five year update.

This presentation considers important developments and new trends related to acoustic injury in the peripheral auditory system reported during the past 5 years. The discussion begins with the effect overstimulation has on the "active" cochlear process, and the associated loss in receptive field (tuning curve) selectivity. Exposure to intense sound also changes the structure and function of the tectorial membrane, sensory hair bundles, tip links, and intracellular organelles. All of these injuries may change the way in which energy is delivered to the transduction channels of the hair cell. Important new evidence describing the quantitative relation between hair cell loss and permanent hearing loss is reviewed, and the possibility that specific exposure conditions cause unique lesions to the inner or outer hair cells is explored. Finally, the importance of hair cell regeneration in the chick cochlea, changes in the CNS following acoustic injury, and the cochlear vascular system are considered.

Animals↗
PubMed1991

The ovine insulin-like growth factor-I gene: characterization, expression and identification of a putative promoter.

Genomic DNA encoding the ovine insulin-like growth factor-I (IGF-I) gene was cloned and sequenced. The predicted amino acid sequence of the mature form of ovine IGF-I was highly homologous to that of human, rat and mouse. Analysis of the DNA sequence between exons 1 and 2 suggested the existence of an alternative 5' exon (exon 1A) and this was confirmed by polymerase chain reaction (PCR) analysis of sheep liver mRNA. Primer extension of mRNA from exon 1A indicated a class of transcripts which initiated at a point 32 nucleotides 5' to the Met codon of exon 1A to give a mRNA comprising exons 1A, 2, 3 and 5. In liver these transcripts co-existed with the alternative exon 1, 2, 3 and 5 mRNA form. Analysis by PCR of the 3' terminus of liver RNA indicated heterogeneity arising from multiple polyadenylation sites; however, of the two possible alternatively spliced 3' exons, only exon 5 could be detected. Expression of IGF-I mRNA, as measured by a solution hybridization/RNase protection assay, predominated in the liver of the neonate and the late-gestation fetus; however, lower levels of expression were seen in multiple tissues throughout fetal and neonatal development.

Amino Acid Sequence↗
PubMed1991

Expression of a growth hormone-responsive exon of the ovine insulin-like growth factor-I gene.

The sheep insulin-like growth factor-I (IGF-I) gene encodes mRNAs containing three different 5'-untranslated sequences as a consequence of alternate splicing of leader exons. Using a combination of RNase protection and primer extension assays, we have mapped the transcriptional start sites of one of the leader exons, exon 1A. Transcription from exon 1A appeared to initiate from multiple points within a 20 bp region situated about 60 bp upstream of the exon 1A splice site. The presence of this transcript in the liver of animals treated with GH was enhanced five- to tenfold and contributed to about 95% of the total hepatic increase in IGF-I mRNA. This exon is generally expressed in a number of tissues immediately after birth; by about 4 weeks postpartum, however, expression is confined to liver. The regulation of hepatic and non-hepatic IGF-I synthesis by GH may involve different mechanisms.

Amino Acid Sequence↗
PubMed1990

Recovery of the basilar papilla following intense sound exposure in the chick.

Newly hatched chicks were exposed to a 900-Hz tone at 120 dB SPL for 48 hours, then sacrificed, along with unexposed controls, at intervals of 0-15 days following exposure. Examination of the basilar papilla by scanning electron microscopy demonstrated a 32% loss of hair cells within the lesion area with substantial shrinkage of the apical surfaces of the survivors. Within days, the papilla returned to a nearly normal appearance, and new hair cells were seen, but the number of new cells was only a fraction--approximately 22%--of the number lost. Expansion of the apical surfaces of the surviving cells to larger than normal size was a major factor in the recovery of the papilla.

Animals↗
PubMed1990

Increased stratum corneum turnover induced by subclinical irritant dermatitis.

The chronic effects of the irritant sodium lauryl sulphate (SLS) on stratum corneum (SC) barrier function, determined by transepidermal water loss (TEWL) measurements and on epidermal cell kinetics, estimated by stratum corneum turnover time (SCTT) determination (dansyl chloride staining method), were investigated in 18 healthy female volunteers. SLS (7.5%) was applied without occlusion for 20 min once daily, over a period of 3 weeks (5 days a week) on dansyl chloride-stained skin and on untreated skin. SCTT of untreated skin (19.3 +/- 0.8 days; mean +/- SEM) was not changed by daily treatment with water (control) (19.3 +/- 2.0) but was significantly reduced by SLS (10.9 +/- 0.6; P less than or equal to 0.0001; compared to controls). However, TEWL was increased in SLS-treated sites 1.5-fold after 4 days of treatment (5.3 +/- 0.6 vs. 3.5 +/- 0.3; P less than 0.001). At the end of the second week, TEWL was increased 2.6-fold and after 3 weeks TEWL was 3.3 times higher than in controls 13.0 +/- 1.6 vs. 3.9, P less than or equal to 0.0001). The intensity of SLS-induced irritation as measured by TEWL was significantly correlated with baseline TEWL (r = 0.50; P less than or equal to 0.02) and significantly negatively correlated with SCTT of SLS treated sites (r = -50; P less than or equal to 0.02) but not with SCTT of untreated skin (r = 0.19).

Adolescent↗
PubMed1989

Recovery of auditory function following intense sound exposure in the neonatal chick.

We report the changes in auditory function that occurred at selected intervals following exposure to an intense pure-tone stimulus. One day old chicks were exposed to a 0.9 kHz tone for 48 h at 120 dB. At 0, 1, 3, 6, 9, 12 and 15 days after exposure, cochlear nucleus sound-evoked potentials were used to assess threshold sensitivity and frequency selectivity. Immediately after removal from the pure tone a threshold shift of 60 dB relative to age-matched controls was measured. The sharpness of tuning curves, as measured by Q10 dB, decreased by over 50%. By post-exposure day 15, near complete recovery of function was seen, with the greatest recovery occurring within the first three days. We relate these results to recent reports of structural recovery on the basilar papilla of the chick.

Animals↗
PubMed1989

Structural changes in hair cells after incubation in tissue culture medium.

A great deal of work is presently being pursued with in vitro preparations of isolated single hair cells or isolated segments of the cochlear sensory surface. In this study we evaluate the appearance of hair cells along the neonatal chick basilar papilla that have been freshly dissected and placed in culture medium for between one and six hours. Quantitative measures of the apical hair cell surface revealed that the number of cytoplasmic protrusions was minimal and that surface area was well preserved in the one and three hour samples. By 6 h, the proportion of hair cells showing cytoplasmic protrusions significantly increased, as did the surface area of the hair cells. In this preparation, it appears that physiologic studies can be conducted on cells with a healthy appearance for at least 3 h after sacrifice.

Adaptation, Physiological↗
PubMed1989

The design, calibration, and use of a water microjet for stimulating hair cell sensory hair bundles.

The design, calibration, and use of a noninvasive, noncontact device for stimulating hair cell hair bundles in vitro are described. This device employed a piezoelectric crystal, driven at high frequencies, to generate sinusoidal pressure in a contained fluid volume. The pressure was propagated to the tip of a glass micropipette and the oscillating water jet stimulus produced at the tip was used to stimulate sensory hair bundles. The movements of glass microbeads, caught in the oscillating pressure field of the water jet, provided a means of calibrating this stimulus. The linearity of the jet, its waveform and frequency response, the influence of pipette shape and tip diameter, as well as models to explain the operation of the water jet, are described. The use of this stimulus for measuring hair bundle micromechanics at high frequencies is then demonstrated.

Animals↗
PubMed1988

When is a residue not a residue?

Residues of veterinary products in food animals have been the subject of much debate in recent years. This paper attempts to define and classify what is meant by the term 'residue' and to discuss the toxicological significance of various types of residues and how they may be controlled to ensure that no hazard results to consumers.

Adolescent↗
PubMed1988

Hair cell loss and regeneration after exposure to intense sound in neonatal chicks.

Neonatal chicks (between 1 and 3 days of age) were exposed to an intense pure tone for 48 hours, then killed immediately after removal from the sound, or 14 days later. Nonexposed age-matched animals served as controls. The inner ear was removed and the auditory receptor organ (the basilar papilla) was prepared for evaluation by scanning electron microscopy. The site of injury on the papilla was described in terms of hair-cell loss and location. The ears with no recovery showed a discrete lesion area, within which there was complete disruption of the hair-cell field and a 35% loss in hair cells. After 14 days' recovery, no hair cell loss could be detected, though the lesion could still be recognized by the disorganization of hair cells in the previously injured area. These data demonstrate hair-cell restoration after severe acoustic injury from intense sound exposure in the neonatal ear.

Animals↗
PubMed1988

From animal to molecule: aspects of the biology of insulin-like growth factors.

The synthesis of IGF-II mRNA in sheep foetal tissues is considerably higher than IGF-I. IGF-II probably has a paracrine role in the foetus; however it is likely that IGF-I originates mainly from the foetal liver and has an endocrine function. Although in the adult system IGF-I is tightly bound to serum carrier proteins it is potentially biologically active. Galactopoiesis in the goat mammary gland provides a useful model for demonstrating the importance of circulating IGF-I as a mediator of GH action. Ligand-receptor interactions involved in the stimulation of Swiss 3T3 fibroblasts by IGF-I, II and insulin were examined. It was found that the potency of binding to type I receptors was IGF-I greater than IGF-II much greater than insulin by competitive binding assays and chemical cross-linking studies, and that some cell lines secrete an IGF binding protein which is specific for IGF-I and II and which acts as an inhibitor in cellular binding assays. Maximal stimulation of DNA synthesis induced by IGF-I, II and insulin in the presence of synergising mitogens were similar. While the actions of the IGFs were consistent with type I receptor binding insulin appeared to act through its own receptor. The reduction of EGF receptor affinity following the addition of IGF-I and insulin to 3T3 cells may involve a protein kinase that is not sensitive to phorbol esters. 3T3 cell nuclei contain endogenous inositol phospholipids and their corresponding kinases and monoesterases.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗