Biomedical subjects

C A McCormick

Publications and source records attributed to C A McCormick.

9 recordsLinked to original sources

PubMed1992

A low cost microprocessor-controlled electrofusion and electroporation system.

An important recent development in the field of biotechnology has been the use of high electric fields to render cell membranes temporarily permeable (electroporation). Cells in this state are receptive to gene transfer or can be induced to fuse with each other (electrofusion) to form hybrid cells containing the combined characteristics of the parent cells. A major reason for fusing cells is to form hybridoma cells which secrete monoclonal antibodies. A problem for research workers has been the high price of some of the electrofusion equipment. This problem has been addressed by designing a device that is inexpensive (less than $800 Canadian) and can be assembled by an electronics technician. The system uses a Radio Shack CoCo III microcomputer which is programmed in BASIC and controls the electroporation voltage pulse amplitude (25-500 V) and duration (2-275 microseconds) to an electrofusion chamber; this yields electric field strengths of 0.25-5 kV cm-1 for a 0.1 cm electrode spacing. The system is capable of delivering pulse currents up to 3 A. This paper provides technical details on how to construct an instrument that has greater flexibility at less cost than comparable commercially available instruments.

Biotechnology↗

PubMed1989

A neuron-specific enhancer of the Drosophila dopa decarboxylase gene.

At least two cis-regulatory elements are necessary for correct neuron-specific expression of the Drosophila melanogaster dopa decarboxylase gene, Ddc. In addition to a previously described proximal element located approximately 60 bp upstream of the mRNA start site, we have now characterized a distal approximately 600-bp DNA fragment, extending from -1019 to -1623 bp, which possesses enhancer-like properties and is essential for normal neuron-specific expression. Immunofluorescent labeling of neurons expressing deleted Ddc genes indicates that this region contains both general neuronal regulatory elements and cell-specific elements that selectively affect Ddc expression in either dopaminergic or serotonergic neurons. These selective effects can be correlated with the removal of sequence elements that are protected from DNase digestion by factors present in embryonic nuclear extracts. Several of these elements are also homologous to sequences located upstream of the evolutionarily diverged Ddc gene of Drosophila virilis. These results suggest that the neuron-specific expression of Ddc results from the combined action of several factors binding within this distal enhancer region.

Animals↗

PubMed1988

The three-dimensional localization of internal mammary lymph nodes by radionuclide lymphoscintigraphy.

In breast cancer patients, radiation therapy planning must account for individual anatomy to ensure optimal coverage of tumor and internal mammary nodes. To achieve this, three-dimensional radionuclide lymphoscintigraphy (RNLS) was performed in 167 patients by obtaining two images of the nodes using a 30-degree slant hole collimator rotated 180 degrees between images. Analysis of 768 nodes (mean 4.6/patient) visualized from the level of rib 1 through interspace 5 was performed. The number of nodes seen was not a function of patient age. Cross-communication to the contralateral node chain occurred in 13.8% of cases. Eighty-two percent of nodes were located near the first three ribs and interspaces; 23% were located beyond 3.0 cm from the mid-sternal line. At the level of the radiation beam match line (second rib or interspace), 4.5% of nodes were deeper than 3.0 cm. From rib 3 through interspace 5, 3.9% were deeper than 3.0 cm. Using an idealized tangential field, at least one node would have been missed in 16.2% of patients. Three-dimensional RNLS allows definition and localization of normal sized nodes and ensures that radiation therapy portals can be tailored for each individual under treatment.

Adult↗

PubMed1986

CNS and hypoderm regulatory elements of the Drosophila melanogaster dopa decarboxylase gene.

Expression of the dopa decarboxylase gene (Ddc) is regulated in a tissue- and developmental stage-specific manner throughout the life cycle of the fruit fly, Drosophila melanogaster. Essential Ddc regulatory elements lie within 208 base pairs upstream from the RNA start point. Functional elements within this 5' flanking region were mapped by deletion analysis, which assayed expression in vivo after germline integration via P element vectors. One of the elements is essential for expression in both the larval and adult central nervous system, and at least two other elements are necessary for quantitatively normal expression in the hypoderm. Within each of the intervals that have regulatory effects are found sequence elements conserved between the Ddc genes of two distantly related species of flies. On the basis of this correlation, regulatory functions for these sequence elements can be postulated.

Animals↗

PubMed1985

Detection of teratogenic substances in acidic mine water samples using the frog embryo teratogenesis assay--Xenopus (FETAX).

The FETAX (Frog Embryo Teratogenesis Assay--Xenopus) whole embryo bioassay has been developed to screen for environmental substances that cause birth defects. We have used this assay to test its effectiveness in working with actual water samples from the field. Tar Creek is contaminated by discharges from abandoned lead and zinc mines. In addition to high concentrations of zinc, iron and other metals, water samples are routinely low in pH and oxygen content. The pH values of three Tar Creek sample sites were below the established tolerance limits of the embryos. Therefore, one group of samples had no pH adjustment while a second group had the pH adjusted to 7.0. Two of the four sites contained agents that reduced embryonic growth and caused high rates of mortality. A third site contained teratogenic substances. We have determined that metal content is responsible, along with the low pH, for the biologic effects. We have identified high concentrations of toxic metals in Tar Creek by water analysis and were able to demonstrate, by removing metals via Chelex 100 ion exchange chromatography, that the observed toxicity and teratogenicity were caused by metal ions. We have concluded that FETAX is an excellent test for complex mixtures. Physicochemical parameters, such as pH, oxygen and metals content, can be altered and the effect of these changes on toxicity and teratogenicity determined using FETAX. The interaction of toxic substances and low pH are important when considering embryo survival and development.

Animals↗

PubMed1985

Clinical comparison of two radiocolloids for internal mammary lymphoscintigraphy.

Recent studies suggest that 99mTc-labeled radiocolloid (SC) compounded with hydrogen sulfide can be used to visualize lymph channels and nodes. Our study prospectively compared SC with 99mTc antimony sulfide (SbS) colloid, in 28 patients undergoing internal mammary lymphoscintigraphy. Images were recorded on a scintillation camera and computer at 0.5, 1.0, and 3.0 hr. Quantitative analysis included assessment of percent (%) injected dose in nodes, the percent remaining at the injection site, and the relative intensity of the most cephalad node compared to a 57Co standard. The mean (means) % injected dose of both radiocolloids within visualized nodes was less than 1% at each time interval, with no significant differences between means's. The means % injected dose remaining at the injection site at 3.0 hr was 83 for SbS and 76 for SC not statistically significant (N.S.). The means of the ratio of counts within the most cephalad node at 3.0 hr to counts within a 57Co standard was 0.98 for SbS and 1.03 for SC (N.S.). Clinical assessment of number of nodes visualized and extent of radiocolloid migration showed no difference between the two agents. The biological and clinical parameters for the two colloids appear similar when used for internal mammary lymphoscintigraphy.

Adult↗

PubMed1984

A horseradish peroxidase procedure for tracing the central projections of peripheral nerves in exsanguinated anamniotes.

This report outlines a procedure for demonstrating the central connections of peripheral nerves in anamniotes by exposing the nerves to horseradish peroxidase (HRP) subsequent to perfusion of the animal with cold saline. The tissue is fixed by immersion after a 6-10 h exposure to the HRP, embedded, sectioned and finally reacted using tetramethylbenzidine as a chromogen. The pattern of afferent projections of the posterior lateral line nerve in the teleost fish Crenicichla as demonstrated by this 'pre-perfused' technique is very similar to the pattern seen when using a standard HRP procedure requiring a post-operative survival period. The utility of the pre-perfused technique is discussed.

Animals↗

PubMed1983

Central connections of the octavolateralis nerves in the pike cichlid, Crenicichla lepidota.

The primary projections of the lateral line and eighth (octavolateralis) nerves in the teleost, Crenicichla lepidota, were found to conform to the pattern of projections of these nerves in non-teleost fishes. The lateral line nerves terminate in the dorsal portion of the octavolateralis area of the medulla, the eighth nerve terminates in the ventral portion of this area, and overlap is restricted to nucleus magnocellularis. An anastomotic connection between the posterior lateral line nerve and the eighth nerve, the lateralis branchlet, is composed of posterior lateral line nerve fibers which enter the medulla with the eighth nerve but terminate with lateral line inputs.

Afferent Pathways↗

PubMed1981

Central projections of the lateral line and eighth nerves in the bowfin, Amia calva.

The first-order connections of the anterior and posterior lateral line nerves and of the eighth nerve were determined in the bowfin, Amia calva, using experimental degeneration and anterograde HRP transport techniques. The termination sites of these nerves define a dorsal lateralis cell column and a ventral octavus cell column. The anterior and posterior lateralis nerves distribute ipsilaterally to two medullary nuclei-nucleus medialis and nucleus caudalis. Nucleus medialis comprises the rostral two-thirds of the lateralis column and contains large, Purkinje-like cells dorsally and polygonal, granule, and fusiform cells ventrally. Nucleus caudalis is located posterior to nucleus medialis and consists of small, granule cells. Anterior lateralis fibers terminate ventrally to ventromedially in both nucleus medialis and nucleus caudalis. Posterior lateralis fibers terminate dorsally to dorsolaterally within these two nuclei. A sparse anterior lateralis input may also be present on the dendrites of one of the nuclei within the octavus cell column, nucleus magnocellularis. In contrast, the anterior and posterior rami of the eighth nerve each terminate within four medullary nuclei which comprise the octavus cell column: the anterior, magnocellular, descending, and posterior octavus nuclei. An eighth nerve projection to the medial reticular formation is also present. Some fibers of the lateralis and eighth nerves terminate within the ipsilateral eminentia granularis of the cerebellum. Lateralis fibers distribute to approximately the lateral half of this structure with posterior lateral line fibers terminating laterally and anterior lateral line fibers terminating medially. Eighth nerve fibers distribute to the medial half of the eminentia granularis.

Animals↗