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Biomedical subjects

M Waring

Publications and source records attributed to M Waring.

11 recordsLinked to original sources
PubMed1991

Absence of both auditory evoked potentials and auditory percepts dependent on timing cues.

An 11-yr-old girl had an absence of sensory components of auditory evoked potentials (brainstem, middle and long-latency) to click and tone burst stimuli that she could clearly hear. Psychoacoustic tests revealed a marked impairment of those auditory perceptions dependent on temporal cues, that is, lateralization of binaural clicks, change of binaural masked threshold with changes in signal phase, binaural beats, detection of paired monaural clicks, monaural detection of a silent gap in a sound, and monaural threshold elevation for short duration tones. In contrast, auditory functions reflecting intensity or frequency discriminations (difference limens) were only minimally impaired. Pure tone audiometry showed a moderate (50 dB) bilateral hearing loss with a disproportionate severe loss of word intelligibility. Those auditory evoked potentials that were preserved included (1) cochlear microphonics reflecting hair cell activity; (2) cortical sustained potentials reflecting processing of slowly changing signals; and (3) long-latency cognitive components (P300, processing negativity) reflecting endogenous auditory cognitive processes. Both the evoked potential and perceptual deficits are attributed to changes in temporal encoding of acoustic signals perhaps occurring at the synapse between hair cell and eighth nerve dendrites. The results from this patient are discussed in relation to previously published cases with absent auditory evoked potentials and preserved hearing.

Acoustic Stimulation↗
PubMed1991

Binding of antibiotics to DNA.

The DNA molecule can serve as host to numerous guest ligands, some of which are antibiotics, and almost all of which are endowed with anticancer or antimicrobial activity. Many guest ligands are quite large and complex in structure, and an array of intermolecular contacts underlie their complementarity to their macromolecular receptor. Often the process of molecular recognition involves conformational adjustments on the part of the interacting species, but the lion's share of the adjusting is demanded of the DNA helix which commonly ends up considerably distorted. Generally the lock must bend to accommodate the key. Two fundamentally different modes of binding can be identified: intercalation and minor groove-binding. The former mode is exemplified by daunomycin or actinomycin and the latter by netropsin or distamycin. Intercalation is associated with substantial extension and unwinding of the helix whereas groove binding is characterized by replacement of the spine of hydration and by lesser effects on helix geometry such as local bending. Bifunctional (or bis-) intercalation, as seen with echinomycin, causes the most far-reaching perturbations in the structure of DNA. It might even involve altered base pairing, which has been observed in complexes between echinomycin and oligonucleotides but has not yet been detected with macromolecular DNA in solution.

Anti-Bacterial Agents↗
PubMed1984

Objective detection of averaged auditory brainstem responses.

Detection of an auditory brainstem response, ABR, usually relies on visual evaluation of two or more data acquisition runs of a fixed number of sweeps to determine if there is sufficient replication of the averaged waveforms to indicate a response. Visual interpretation can be difficult when the signal-to-noise ratio is poor because of either a small response or high levels of physiological background noise. Moreover, variations in the background noise from run to run can result in poor or spurious replications of component peaks and troughs in the waveform. A previous study (Elberling & Don, 1984) described a statistical approach for objective evaluation of the quality of an ABR recording. The method uses variance analysis in calculating the ratio of the magnitude of the ABR to the estimated averaged background noise. This study further applies this method to obtain a quantitative definition of the ABR threshold, to demonstrate its application in automatic threshold detection, and to estimate the number of sweeps required to reach detection criterion. Application of this method is valuable in reducing the variability of test interpretation and in maximizing the efficiency of recording ABRs by avoiding the averaging of excessive or insufficient numbers of sweeps. These improvements enhance the cost-benefit of ABR testing to the patient.

Adult↗
PubMed1966

Nucleotide sequence repetition: a rapidly reassociating fraction of mouse DNA.

The separated complemnentary strands of a minor component in mouse DNA reassociate with each other much more rapidly than do the complementary strands of other DNA's including those of the principal part of mouse DNA. This difference in capacity of the strands to reassociate can be used to effect a preparative separation of the minor component from the principal fraction. The rate constant for reassociation of the minor component, compared with those of viral and bacterial DNA's, indicates that the minor component consists of a short nucleotide sequence present in about one million copies.

Amino Acid Sequence↗