Biomedical subjects

K H Huynh

Publications and source records attributed to K H Huynh.

5 recordsLinked to original sources

PubMed2005

Cochlear function in mice with only one copy of the prestin gene.

Targeted deletion of the prestin gene reduces cochlear sensitivity and eliminates both frequency selectivity and outer hair cell (OHC) somatic electromotility. In addition, it has been reported by Liberman and colleagues that F2 generation heterozygotes exhibit a 6 dB reduction in sensitivity, as well as a decrease in protein and electromotility. Considering that the active process is non-linear, a halving of somatic electromotility would be expected to produce a much larger change in sensitivity. We therefore re-evaluated comparisons between heterozygotes and wildtype mice using both in vivo and in vitro electrophysiology, as well as molecular biology. Data reported here for F3-F5 generation mice indicate that compound action potential thresholds and tuning curves, as well as the cochlear microphonic, are similar in heterozygotes and wildtype controls. Measurements of non-linear capacitance in isolated OHCs demonstrate that charge density, as well as the voltage dependence and sensitivity of motor function, is indistinguishable in the two genotypes, as is somatic electromotility. In addition, both immunocytochemistry and western blot analysis in young adult mice suggest that prestin protein in heterozygotes is near normal. In contrast, prestin mRNA is always less than in wildtype mice at all ages tested. Results from F3-F5 generation mice suggest that one copy of the prestin gene is capable of compensating for the deleted copy and that heterozygous mice do not suffer peripheral hearing impairment.

Animals↗

PubMed2004

Cochlear function in Prestin knockout mice.

Gross-potential recordings in mice lacking the Prestin gene indicate that compound action potential (CAP) thresholds are shifted by approximately 45 dB at 5 kHz and by approximately 60 dB at 33 kHz. However, in order to conclude that outer hair cell (OHC) electromotility is associated with the cochlear amplifier, frequency selectivity must be evaluated and the integrity of the OHC's forward transducer ascertained. The present report demonstrates no frequency selectivity in CAP tuning curves recorded in homozygotes. In addition, CAP input-output functions indicate that responses in knockout mice approach those in controls at high levels where the amplifier has little influence. Although the cochlear microphonic in knockout mice remains approximately 12 dB below that in wild-type mice even at the highest levels, this deficit is thought to reflect hair cell losses in mice lacking prestin. A change in OHC forward transduction is not implied because knockout mice display non-linear responses similar to those in controls. For example, homozygotes exhibit a bipolar summating potential (SP) with positive responses at high frequencies; negative responses at low frequencies. Measurement of intermodulation distortion also shows that the cubic difference tone, 2f(1)-f(2), is approximately 20 dB down from the primaries in both homozygotes and their controls. Because OHCs are the sole generators of the negative SP and because 2f(1)-f(2) is also thought to originate in OHC transduction, these data support the idea that forward transduction is not degraded in OHCs lacking prestin. Finally, application of AM1-43, which initially enters hair cells through their transducer channels, produces fluorescence in wild-type and knockout mice indicating transducer channel activity in both inner and outer hair cells.

Acoustic Stimulation↗

PubMed1990

Lack of specificity of DA/DAPI fluorescence.

Cytogenetic studies showed 47,XY, + mar in a developmentally retarded child with some features of Prader-Willi syndrome, and 46,XX in his mother. The marker chromosome showed a single subterminal primary constriction, bisatellites, and two C-bands. DA/DAPI staining showed two intense bands in the marker chromosome, which most likely was derived from chromosome 15. Intense DA/DAPI fluorescence was also found in one chromosome 13 in the child, and one 13 and one 10 in his mother. The present results confirm the reports of DA/DAPI heteromorphism in acrocentric chromosomes other than the 15, and demonstrate a pericentric DA/DAPI heteromorphism in chromosome 10.

Adult↗

PubMed1980

[Blood pressure during pediatric anesthesia. Four methods of peroperative indirect measurement. Comparison (author's transl)].

During general anesthesia blood pressure levels have been recorded for 35 children (10 aged 1-12 months, 15 aged 12-24 months, 10 more than 24 months). Four different methods of indirect measurement were used: pulse palpation, flush technique, ausculatory determination by mean of a conventional sphygmomanometer, Doppler ultrasonic technique by mean of arteriosonde. The pulse palpation is the easiest method at any age, during pediatric anesthesia but does not give values of diastolic blood pressure. The flush technique quite convenient for infants less than 24 months gives values lying midway between systolic and diastolic blood pressure. Ausculatory determination in operating room is difficult especially with small infants less than 12 months. During anesthesia longer than thirty minutes, monitoring blood pressure by Doppler ultrasound sphygmomanometer can be fairly available. Even in case of difficulties to detect clear signals of systolic and diastolic blood pressure the sphygmomanometer can be used to obtain blod pressure determination by flush technique or pulse palpation.

Age Factors↗

PubMed1976

[Electronic surveillance during delivery. A method of reading the tracings].

A method for reading the foetal heart rate tracings and a guide of management advise in each case have been established from a review of the literature and the study of 500 records. The tracings are schematically divided into three categories according to the presumed risk of foetal distress: normal or "tolerable" tracings, alarm symptoms and danger symptoms. For each categorie, and according to the duration of the variations, a type of management is proposed. Other diagnostic means, such as capillary blood pH measurement are desirable to improve the foetal state diagnostic and make the treatment more precise.

Adult↗