Biomedical subjects

D Prasher

Publications and source records attributed to D Prasher.

29 records · Page 2Linked to original sources

PubMed1988

The value of combining auditory brainstem responses and acoustic reflex threshold measurements in neuro-otological diagnosis.

Acoustic reflex thresholds (ART) and auditory brainstem responses (ABR) were measured in 69 patients referred to the Neuro-otological clinic on the suspicion of a retrocochlear lesion. The pure-tone selection criterion was an average hearing loss of less than 60 dB at 0.5, 1, 2, and 4 kHz, with no thresholds exceeding 70 dB and only one threshold exceeding 60 dB. Both tests proved independently to be most effective in the diagnosis of cerebello-pontine angle (CPA) tumours and to a lesser extent for brainstem lesions. The ABR was positive in 100% of CPA group and 90% in the brainstem group compared with 93% and 70% respectively for the ART. The combination of the two tests provides patterns of abnormality which are more disease specific. In the CPA cases the most common and consistent patterns of abnormality were the unilateral delay of Wave V or III and V of the ABR associated with a vertical ART pattern indicative of an abnormality of the ipsi and contralateral reflexes on stimulating the affected side. Intrinsic brainstem lesions most commonly resulted in bilateral ABR abnormalities combined with the full-house ART pattern indicative of bilateral abnormalities of both ipsi and contralateral reflexes.

Adolescent↗

PubMed1987

Intra-operative electrocochleography to monitor cochlear potentials during acoustic neuroma excision.

Intra-operative electrocochleography (ECochG) was used in an attempt to monitor the action potential of the cochlear nerve during acoustic neuroma surgery in 14 patients with useful pre-operative hearing. Five patients had ECochG potentials preserved and yet only three could hear when tested audiometrically later. Of those losing the potentials intra-operatively all were subsequently deaf and the pattern of waveform loss allowed determination of the probable cause of hearing loss. Complete excision of the tumour was achieved in each case regardless of the ultimate effect on the AP as it was not felt justified to risk subsequent recurrence. In common with other studies one of the best prognostic factors for these preservation of hearing was found to be the size of the tumour.

Adult↗

PubMed1987

Preservation of cochlear potentials in a deaf patient fifteen months after excision of an acoustic neuroma.

Intraoperative electrocochleographic monitoring has been used in an attempt to protect cochlear nerve function during acoustic neuroma excision. One patient is presented with an apparently intact cochlear nerve and waves N1 and N2 preserved at the end of surgery, but no hearing on subsequent testing. Fifteen months after operation, cochlear microphonics and the summating potential were still present, but N1 and N2 had disappeared. There had been no improvement in her hearing and there were no consistent brainstem auditory evoked potentials on the affected side. A possible explanation for these findings is given.

Adult↗

PubMed1986

Brain stem auditory evoked potentials in patients with multiple system atrophy with progressive autonomic failure (Shy-Drager syndrome).

Brain stem potentials from three groups of patients, namely those with pure progressive autonomic failure, Parkinson's disease and multisystem atrophy with progressive autonomic failure (Shy-Drager syndrome) were compared with each other and a group of normal subjects. In virtually all the patients with multisystem atrophy with progressive autonomic failure the brain stem potentials were abnormal in contrast to normal findings with Parkinson's disease. The closely associated group of patients with progressive autonomic failure alone also revealed no abnormalities of the BAEP. This separation of the two groups, Parkinson's disease and progressive autonomic failure from multisystem atrophy with progressive autonomic failure is important clinically as multiple system atrophy of the Shy-Drager type has extra-pyramidal features closely resembling Parkinsonism or a late onset cerebellar degeneration. From the abnormalities of the brain stem response in multisystem atrophy with progressive autonomic failure, it is clear that some disruption of the auditory pathway occurs in the ponto-medullary region as in nearly all patients there is a significant delay or reduction in the amplitude of components of the response generated beyond this region. The most likely area involved is the superior olivary complex.

Aged↗

PubMed1985

High-affinity calcium-binding proteins in Escherichia coli.

Crude extracts of Escherichia coli contain at least three heat stable proteins of Mr, 33,000, 47,000, and 60,000, which bind 45Ca2+ in buffers containing micromolar calcium and physiological salt concentrations. Fractions containing these proteins neither activated the calmodulin-dependent enzyme, NAD kinase, nor inhibited the activity of this enzyme in the presence of brain calmodulin. Radioimmunoassay of crude extracts for calmodulin indicated the presence of a calmodulin-like antigen. Crude extracts also contain proteins that interact with 2-trifluoromethyl-10H-(3'-aminopropyl)phenothiazine-Sepharose in a calcium-dependent manner, but proteins eluted from this resin did not bind calcium with high affinity.

Buffers↗

PubMed1985

Cloning and expression of the cDNA coding for aequorin, a bioluminescent calcium-binding protein.

Aequorin is a bioluminescent protein which consists of a polypeptide chain (apoaequorin), coelenterate luciferin, and bound oxygen. Aequorin produces blue light upon binding Ca2+. We have isolated six recombinant pBR322 plasmids which contain apoaequorin cDNA sequences. A mixed synthetic pBR322 plasmids which contain apoaequorin cDNA sequences. A mixed synthetic oligonucleotide probe was used to identify these cDNAs. An extract of an E. coli strain possessing the largest cDNA contained apoaequorin. This apoaequorin can be converted to aequorin in the presence of coelenterate luciferin, 2-mercaptoethanol, and O2. This cDNA is therefore apparently full-length.

Aequorin↗

PubMed1984

Physical and biochemical analysis of the cloned recB and recC genes of Escherichia coli K-12.

A 19-kilobase BamHI fragment encoding the recB (exonuclease V), recC (exonuclease V), ptr (protease III), thyA, and argA genes of Escherichia coli K-12 was cloned into a multicopy plasmid (pCDK3). In E. coli maxicells, the plasmid specified the synthesis of seven polypeptides of 140,000 (recC), 128,000 (recB), 110,000 (ptr), 53,000 (argA), 50,000, 33,000 (thyA), and 22,000 Mr, as well as beta-lactamase and chloramphenicol acetyltransferase. From analysis of subclones and Tn1000 insertions, it appears that the 110,000- and 50,000-Mr proteins originated from the ptr DNA coding sequence which is located between the recB and recC genes. Although recC, ptr, and recB were physically closely linked and transcribed in the same direction, they do not appear to constitute an operon. Cells carrying pCDK3 contained a 30- to 50-fold increase in exonuclease V activity, without affecting cell viability.

Cloning, Molecular↗

PubMed1984

Neuro-otological abnormalities in Friedreich's ataxia.

Ten patients with an accepted diagnosis of Friedreich's ataxia have been examined neuro-otologically, and oculomotor, vestibular and auditory function assessed. Brainstem auditory evoked potentials (BAEPs) were also recorded. A high incidence of various eye movement disorders was noted. Some of these were indicative of cerebellar dysfunction. Reduced vestibular function and impaired hearing were common to most of the patients. BAEPs were also abnormal in the majority; reasons underlying these abnormalities are discussed. Neuro-otologically, the patients did not constitute an homogeneous group. The findings cast doubt upon the accuracy and validity of the currently accepted criteria for the diagnosis and classification of the spinocerebellar degenerations.

Adolescent↗

PubMed1983

Physical and genetic characterization of the cloned sbcB (exonuclease I) region of the Escherichia coli genome.

A 17-kilobase (kb) HindIII fragment containing the structural gene for exonuclease I (sbcB) from Escherichia coli K-12 was physically and genetically characterized. The monomeric molecular weight of exonuclease I was 53,700, based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 35S-labeled E. coli mini- and maxicells. The gene was in close proximity to two unidentified proteins with molecular weights of 15,200 and 13,100. No other polypeptides appeared to be constitutively synthesized from the 17-kb fragment. Genetically, no portion of the histidine operon or the shikimic acid transport gene (shiA) was detected on the fragment. Although the entire 17-kb fragment in the vector pMB9 was too unstable to be useful, a 7.6-kb BamHI-EcoRI fragment inserted into a variety of vectors was stable. A detailed restriction map of the fragment is presented. Several derivatives in the runaway-replication vectors pMB06 and pMOB45 yielded 20- to 52-fold increases in exonuclease I activity after a switch in growth temperature to 40 degrees C. Of six exonuclease I mutants examined by DNA-DNA hybridization, one (xonA6) appeared to have arisen from a 1.2-kb insertion into the structural gene for exonuclease I.

Cloning, Molecular↗

PubMedDate not supplied

Contralateral suppression of transiently evoked otoacoustic emissions and neuro-otology.

Transiently evoked otoacoustic emissions can be suppressed with simultaneous contralateral sound stimulation. This is considered to be effected via the efferent pathway from the superior olivary complex (SOC) to the contralateral cochlea. This study examined this effect in patients with extrinsic and intrinsic lesions of the brainstem which may affect the efferent pathway either within the vestibular nerve which carries the efferent bundle to the cochlea or within the brainstem at the level of the SOC. Suppression is reduced or absent in these patients and the site and size of the lesion determines whether the suppression is affected unilaterally or bilaterally. Lesions affecting the auditory afferent pathway without significant alteration in hearing appear to affect the efferent pathway too.

Acoustic Stimulation↗

PubMedDate not supplied

Confounding or aggravating factors in noise-induced health effects: air pollutants and other stressors.

Different scientific groups have studied and continue to study the health impacts of physical and chemical agents in the environment. In most cases, every study group has considered the health effect as being solely due to the air pollutant(s) under investigation, for example air pollution without due regard for the simultaneous presence of noise pollution whereas both have an impact on the cardiovascular system. Or in the case of noise studies the contribution of solvent, asphyxiant or metal exposures has not been considered, which can have an impact on hearing impairment. One can, therefore, question the stringency of the available evidence of epidemiological studies in both fields to warrant the consideration of air pollutants as confounding or aggravating factors in studies of specific effects due to noise (and vice versa). In this paper we weigh the existing evidence on the association of noise and air pollutant exposure and associated health impacts. In forthcoming publications, the authors will consider the influence of other factors, which can confound noise studies but are currently not included in the analysis.

Air Pollution↗