Biomedical subjects

Q T Nguyen

Publications and source records attributed to Q T Nguyen.

4 recordsLinked to original sources

PubMed1992

Neurokinin A (NK2) receptor revisited with SR 48968, a potent non-peptide antagonist.

SR 48968, a new non-peptide antagonist of NK2 receptors, has been tested in a variety of isolated smooth muscle preparations from rats, guinea pigs, rabbits, hamsters and men, in order to assess its selectivity for NK2 receptors as well as its competitivity and specificity. The compound has been found to be inactive as a stimulant or relaxant in all preparations but to exert a potent, competitive antagonism, particularly in tissues obtained from rabbits (pA2 9.8-10.3), guinea pigs (10.5), rats (9.4-9.6), men (9.36-9.6) and hamsters (7.45-8.6). SR 48968 is therefore more active on the NK2A than on the NK2B receptor subtype and the human receptor is close to the NK2A subtype. SR 48968 exerts an antagonism of the competitive type and is therefore suitable for receptor classification despite its slow reversibility in vitro. The sensitivity of NK2A receptors to SR 48968 is at least 1000 times higher than those of NK1 and NK3 receptors. The compound does not affect the effects of bradykinin, angiotensin or bombesin. Because of its activity in human tissues, its potency and long duration of action, SR 48968 is a new promising pharmacologic and possibly therapeutic agent.

Animals↗

PubMed1992

Discrimination of narrow-band spectra. I: Spectral weights and pitch cues.

The ability to detect changes in the spectral shape of narrow-band tonal complexes (spectral profiles) is examined. The standard consists of three tones of equal intensity; thresholds for detecting an increment in the level of the central, 1000-Hz tone are estimated. A roving-level procedure is used in order to impose a statistical limit on thresholds that can be obtained by basing discriminations on absolute intensity. Estimated thresholds are consistently below this limit, thus indicating the use of other cues. Generally, thresholds are constant for bandwidths ranging from less than a critical band to greater than several octaves. Spectral weight estimates, however, are highly dependent on bandwidth, providing evidence that the discrimination of narrow-band spectra involves different auditory processes than those used to discriminate wideband spectra. Additional data show that pitch cues are important within a restricted range of intermediate bandwidth, but not for wideband or very narrow-band spectra. A version of the EWAIF model involving off-frequency listening is proposed to account for the results.

Adolescent↗

PubMed1991

Demonstration of a divergent transcript from the bidirectional heavy chain immunoglobulin promoter VH441 in B-cells.

The mouse heavy chain immunoglobulin promoter VH441 can lead in vitro to bidirectional transcription, due to a symmetrical organization of immunoglobulin heavy chain promoters with two TATA-like sequences bracketing the upstream promoter element ATGCAAAT (the so called octamer). We demonstrate here that divergent transcription also occurs in vivo in mature B cells from a myeloma which expresses the VH441 gene and even from the spleen of BALB/c mice. The level of VH441 divergent transcript increases in the spleen of BALB/c mice after immunisation by beta-(1,6)-galactan, showing that it is expressed in B cells which actively transcribe the VH441 gene. The divergent transcript has been characterized: its major transcription start site was mapped within 33 base pairs from the divergent TATA-like region, it is unspliced and not polyadenylated. In the light of these results, the functions of the divergent transcript and the bidirectional promoter are discussed.

Animals↗

PubMedDate not supplied

Profile analysis: detecting dynamic spectral changes.

This paper explores how amplitude modulation influences the detection of changes in spectral shape. We generally used a complex of 21 equal-amplitude components, the lowest frequency was 200 Hz, the highest 5000 Hz, with equal logarithmic spacing between components. The signal was an increase in level of one or more components of the complex. The overall level of the sound varied randomly over a 20-dB range. Three experiments are reported. In the first, we determined how the modulation of a single-frequency component influenced the detection of amplitude change at that region. In the second experiment, the signal was an alteration of the entire spectrum and that alteration was subjected to various forms of amplitude modulation. In neither experiment did modulation generally increase the detectability of the signal. Finally, in the third experiment, we determined the effects of modulating the 'signal' and 'nonsignal' parts of the spectrum in different relative phases. The results of this experiment showed that the relative phase is important only for modulation rates slower than about 40 Hz. For faster rates, the temporal structure of the spectrum is unimportant. Thus, for modulation rates above 40 Hz, only the power spectrum of the stimulus is critical.

Acoustic Stimulation↗