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Biomedical subjects

N Raghavan

Publications and source records attributed to N Raghavan.

17 recordsLinked to original sources
PubMed1992

Identification of a repetitive element in the snail Biomphalaria glabrata: relationship to the reverse transcriptase-encoding sequence in LINE-1 transposons.

BamHI-digested Biomphalaria glabrata DNA contains a repetitive 2.0-kb fragment which is readily discernible by ethidium bromide staining. We present evidence that this repetitive element is related at both the nucleotide and amino acid levels to long interspersed nuclear element (LINE)-like transposons. Although comparable elements have been described in several invertebrates, this is the first report of a molluscan homologue. In common with LINE transposons, an open reading frame in the B. glabrata element shows significant homology to reverse transcriptase--a feature believed to allow the dissemination of these elements in the eukaryotic genome.

Amino Acid Sequence↗
PubMed1992

Characterization of a muscle-associated antigen from Wuchereria bancrofti.

A recombinant clone, WbN1, isolated from a genomic expression library of Wuchereria bancrofti and showing restricted specificity at the DNA level (Southern and PCR analyses) for Wuchereria bancrofti and Brugia malayi has been previously described. Sequence analysis of WbN1 indicated that it had notable similarity to myosin. Further characterization using in situ hybridization has localized the mRNA in the muscle of the adult parasite and in the microfilariae. Rabbit polyclonal antiserum, raised against the recombinant WbN1 fused to the maltose-binding protein, recognized a 200-kDa polypeptide in immunoblots containing B. malayi antigen extracts. The same antibody also recognized myosin extracted from Brugia pahangi, Onchocerca volvulus, and Caenorhabditis elegans. Localization using the rabbit antiserum revealed the presence of the antigen in the adult muscle tissue and in the microfilariae; the same antibody inhibited the binding of a monoclonal antibody 28.2 (directed toward MHC B of C. elegans myosin) to the recombinant WbN1 antigen and also to purified C. elegans myosin. Based on homology data, structural location, competitive ELISA, and immunoblot we conclude that WbN1 is related to myosin or a similar myofibrillar protein.

Amino Acid Sequence↗
PubMed1991

Cloning and characterization of a species-specific repetitive DNA sequence from Loa loa.

A genomic DNA library of Loa loa was constructed in lambda gt11 using EcoRI-digested DNA from microfilariae isolated from two West African patients. Screening with labeled L. loa DNA yielded several potential repetitive DNA clones. An MboI fragment of one of these, LL3M9, was identified and characterized. Sequence analysis of LL3M9 revealed an 839-bp fragment with an unusual 356-bp region containing 37 copies of the hexamer CTTAGG, many of which are arranged in repeated motifs of 12, 27 and 63 bp. This region shares many of the characteristics of eukaryotic satellite DNA. A synthetic oligonucleotide corresponding to the 27-bp repeated motif, LL3M9REP, was found to be both sensitive and species-specific by dot hybridization. Species specificity of LL3M9REP was confirmed by amplification of the repetitive region using genomic DNA as a template in the polymerase chain reaction.

Animals↗
PubMed1991

A recombinant clone of Wuchereria bancrofti with DNA specificity for human lymphatic filarial parasites.

In order to understand the immune response to Wuchereria bancrofti and to aid in the diagnosis of W. bancrofti infections, recombinant antigens were identified from a W. bancrofti genomic expression library made in lambda gt11 using a pool of sera from infected Indian patients. One of the recombinant clones, lambda WbN1, containing a 2.5-kb insert, reacted strongly to a pool of sera from patients with lymphatic filariasis but not to normal human sera. In addition, this clone showed restricted specificity at the genomic level to the major lymphatic filarial parasites W. bancrofti and Brugia malayi but not to the closely related filarial parasite Brugia pahangi or to other filarial and non-filarial species tested. Nucleotide sequence analysis indicated the cloned DNA to have homology to myosin-like myofibrillar proteins. Polymerase chain reaction amplification initiated by specific synthetic oligomers amplified DNA in a species-specific manner from as little as 16 pg of isolated DNA or from one microfilaria.

Amino Acid Sequence↗
PubMed1989

Context-based automated detection of epileptogenic sharp transients in the EEG: elimination of false positives.

This paper describes a knowledge-based system for the elimination of false positives in the automated detection of epileptogenic sharp transients in the EEG. The system makes comprehensive use of spatial and temporal context information available on 16 channels of EEG, EKG, EMG, and EOG. A knowledge-based implementation is used because of the ease with which it allows the contextual rules to be expressed and refined. The resulting system is shown to be capable of rejecting a wide variety of artifacts commonly found in EEG recordings, artifacts that cause numerous false positive detections in systems making less comprehensive use of context.

Artificial Intelligence↗
PubMed1989

MR imaging in the tethered spinal cord syndrome.

MR examinations of the spine were reviewed in 25 patients with a clinical diagnosis of tethered spinal cord. In 21 patients (84%), the level of the tip of the conus was below the mid L2 vertebral body. The causes of the tethering were spinal lipomas (72%), tight filum terminale syndrome (12%), diastematomyelia (8%), and myelomeningocele (8%). These entities were readily identified in all instances. Bony dysraphisms were well demonstrated by MR. Interestingly, cavitary lesions/myelomalacia of the conus or the cord adjacent to the tethering lesion were seen with appropriate images in nine of 20 patients. This unexpected finding may have diagnostic and/or prognostic significance. Spinal MR was found to be extremely useful in the evaluation of the suspected tethered spinal cord. It was able to visualize the conus medullaris, assess the thickness of the filum terminale, identify traction lesions, and evaluate associated bony dysraphisms.

Adolescent↗
PubMed1987

A note on the effect of gamma-rays on cefamandole and oxacillin.

The feasibility of the radiation sterilization of two beta-lactam antibiotic powders, cefamandole nafate and oxacillin sodium, has been examined by subjecting them to a range gamma-radiation doses, followed by chemical and microbiological analyses. It would appear feasible to radiation sterilize oxacillin sodium. The radiation sterilization of cefamandole nafate may be realistic at low doses or under conditions that minimize radiolysis.

Cefamandole↗
PubMed1986

A novel radiotracer method for the precise determination of water vapor transmission rate characteristics of packaging systems.

A novel analytical method is described for sensitive determination of moisture transmission characteristics of packaging systems. In this method, moisture uptake is measured by a radiotracer technique that utilizes tritium-labeled water (HTO). This technique is specific for actual water ingress, unlike weight gain methods, which require blanks to correct for water absorbed by the packaging materials. Because the amount of water transmission necessary for detection decreases with increasing activity of the water in the incubation chamber, the method can be made much more sensitive than gravimetric methods. The sensitivity of the radiotracer method permitted analysis of moisture entry modes of container systems. Also described herein is the applicability of various desiccants for use in the radiotracer method, discussed in terms of isotope effects and proton exchange.

Absorption↗
PubMed1985

Application of indirect photometric chromatography to pharmaceutical analysis.

Indirect photometric chromatography, which couples analyte separation by ion exchange with indirect photometric detection, is applied to the analysis of complex solutions encountered in the pharmaceutical industry. Applications of primary interest include simultaneous acetate, lactate, chloride, or phosphate determinations, a bisulfite/sulfate assay, and quantitation of trace levels of chloride in deionized water. Three commercially available ion chromatography columns are studied for their suitability in these applications. Due primarily to (A) the acid-base chemistry of the phosphate and bisulfite ions, (B) the need to stabilize the readily oxidized bisulfite, and (C) resin stability at high pH, the column packed with a polymer-based resin is capable of producing analytically superior separations of Cl-, HPO4-2, and matrix components and of SO3-2/SO4-2 in the samples of interest. Under rigid relative concentration conditions, the columns packed with a silica backbone resin are capable of separating acetate, lactate, Cl-, and H2PO4- with baseline resolution and are effective for determining Cl- levels at concentrations of less than one part-per-million.

Acetates↗
PubMed1980

Bacteriophage T4-related macromolecular synthesis under restriction of plasmid Rts1.

Rts1 is a plasmid which confers upon the host bacteria the capacity to restrict T4 bacteriophage growth at 32 degrees C but not at 42 degrees C. Pulse-labeling of phage-infected cells showed that Rts1 restricts the synthesis of T1 DNA. Despite efficient restriction of T4 phage growth and DNA synthesis, infected Escherichia coli 20SO harboring Rts1 synthesized both early and late T4 phage RNA. Synthesis of early T4 phage RNA under restrictive conditions (32 degrees C) was almost equal to that found under nonrestrictive conditions, and a lesser, but significant, amount of late T4 phage RNA was made in almost complete absence of T4 DNA synthesis. Moreover, very little, if any, T4 phage-coded lysozyme was detected in the infected E. coli 20SO/Rts1 at 32 degrees C, whereas normal amounts of lysozyme were present at 42 degrees C.

DNA Restriction Enzymes↗
PubMedDate not supplied

Eliminating interferences in a compendial test for oxidizable substances in water.

The United States Pharmacopoeia (USP) uses acidified potassium permanganate to test for dissolved organics in pharmaceutical-grade water. In the test, a standard permanganate concentration is added to a boiling, acidified water sample. Visually inspecting the sample for residual permanganate determines whether the sample passes (pink color remains) or fails (pink color disappears) the test. The permanganate redox chemistry is complex, however, and test samples are prone to developing suspended particulate and colors other than pink. Forming hazy or off-colored solutions interferes with the subjective end point determination according to the USP test. We report two alternative end point determinations that essentially eliminate interferences from the compendial test method. The first alternative involves recording a uv-visible spectrum of the reduced permanganate test solution. Residual permanganate shows three distinct absorbance maxima at 510, 526, and 545 nm. It is straightforward to differentiate the characteristic permanganate fingerprint from the broad, lower-wavelength extinction that results from interfering substances. The second alternative involves filtering the reduced permanganate test solution through sintered glass. This filtration step removes manganese oxides and other colloidal particles that contribute to haze and off color formation in test samples. Visually inspecting the filtrate for residual pink color remains the end point determination for the test method. A third alternative method, namely spectrophotometric determination of permanganate loss rate constants is not a suitable alternative owing to a strong dependence of permanganate reduction rate on organic substrate structure.

Filtration↗
PubMedDate not supplied

The wedge-shaped cord terminus: a radiographic sign of caudal regression.

Imaging studies from 13 patients with caudal regression were reviewed retrospectively to assess the spectrum and findings of this anomaly. Seven patients were evaluated with MR and six with myelography (supplemented with CT in three). The level of regression varied from T9 to the coccyx. Although osseous abnormalities were more readily identified and characterized by CT, MR effectively depicted the level of vertebral regression, presence of central spinal stenosis, and vertebral dysraphic anomalies. MR demonstrated a characteristic wedge-shaped (longer dorsally) cord terminus in seven of the patients. When this characteristic cord terminus is seen, imaging of the lower lumbar and sacral regions should be performed to verify the diagnosis of caudal regression. Tethered spinal cords have been described in patients with caudal regression and were seen in two of our patients. We present the first cases of individuals who have survived with absence of vertebrae above the T10 level and an unusual case of caudal regression with absent lumbar vertebrae and preserved lower sacral and coccygeal vertebrae. The syndrome of caudal regression encompasses a wide spectrum of pathology that is analyzed well by modern imaging techniques.

Adolescent↗