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Biomedical subjects

M Spencer

Publications and source records attributed to M Spencer.

At least 73 records · Page 4Linked to original sources
PubMed1991

Membrane skeleton protein 4.1 in inner segments of retinal cones.

Retinal cone photoreceptors are polarized cells with discrete functional compartments. Little is known of the membrane-skeleton components in cones responsible for the maintenance of cellular morphology and compartmentalization of integral membrane proteins. The authors describe a high density of the membrane-skeleton protein 4.1 in the myoid region of cones in retinas of developing and adult frogs, and adult lizards, turtles, and chicks. In the developing retina, a discrete locus of protein 4.1 is first detected by immunocytochemistry in the cone myoid after the completion of photoreceptor synaptogenesis. Protein 4.1 immunoreactivity expands to line the plasma membrane of the myoid after cones attain their adult proportions. Nonerythroid alpha-spectrin and protein 4.1 colocalize in the cone myoid, and both are in close proximity to long bundles of f-actin that traverse the myoid and extend from the cone outer segment to the external limiting membrane. By analogy to the erythrocyte, where protein 4.1 modulates the interaction of spectrin and actin to regulate cell shape, the authors propose that protein 4.1 interacts with nonerythroid alpha-spectrin and f-actin in cones and plays a role in the maintenance of cone inner segment morphology.

Actins↗
PubMed1990

Membrane skeleton protein 4.1 in developing Xenopus: expression in postmitotic cells of the retina.

Membrane skeleton protein 4.1 plays a key role in modulating the interactions of spectrin, actin, and integral membrane proteins in erythroid and nonerythroid cells. We have investigated its structure and expression during embryonic development of Xenopus laevis. An analysis of the complete 2758-nucleotide sequence and predicted translation of 801 amino acids (85.5 kDa) of X. laevis oocyte protein 4.1 reveals that, within overlapping regions, oocyte protein 4.1 is 74% identical to a composite amino acid sequence of human erythroid and lymphoid protein 4.1 and has an identity similar to that of amino acid motifs variably expressed in either human erythroid or lymphoid protein 4.1 S1 nuclease protection analysis demonstrates the presence of a single species of protein 4.1 transcript in embryos. Antibodies produced against X. laevis protein 4.1 fusion protein recognize two bands of 180 and 115 kDa on Western blots of X. laevis embryos and retina and, using immunocytochemical techniques, label the developing retina most intensely. In vitro transcription of a cDNA construct fully encoding X. laevis protein 4.1 yields a synthetic mRNA which, when translated in vitro, produces a polypeptide that comigrates on SDS-polyacrylamide gels with the 115-kDa form of embryos and retina. Protein 4.1 is found exclusively in photoreceptors following the terminal mitosis of retinal neurons. When retinal synaptogenesis is complete, protein 4.1 is also expressed in the inner retina. In adult amphibian retinas, protein 4.1 is detected in photoreceptors, bipolar cells, and ganglion cell axons. As these cell types have previously been shown to express spectrin, actin, and ankyrin, it is likely that the membrane skeleton of erythrocytes and retinal cells share functional similarities.

Amino Acid Sequence↗
PubMed1990

Design and testing of external fixator bone screws.

In external fixation, bone screw loosening still presents a major clinical problem. For this study, the design factors influencing the mechanics of the bone-screw interface were analysed and various experimental screws designed with the intention of maximizing the strength and stiffness of the inserted screw. Push-in, pull-out and bending tests were then carried out on the three experimental screws, and on two commercially available screws in both a synthetic material and in cadaveric bone; photoelastic tests on different screw threadforms were also performed. The results of the push-in and pull-out tests indicate that both the screw threadform and cutting head have a significant effect on the holding strength of the screw. The photoelastic tests show that most of the applied load is distributed over the first few threads closest to the load, and that the area between the thread crests is subjected to high shear stresses.

Biomechanical Phenomena↗
PubMed1990

Long-term follow-up of the ileoanal anastomosis in children and young adults.

The purpose of this study was to carry out a long-term study of the ileoanal anastomosis (IAA) in children and young adults, comparing the straight IAA to the J pouch. One hundred twenty-one young people who had undergone IAA were studied, with 114 available for long-term follow-up. One hundred one were 18 years and under. Forty-nine patients had a straight IAA and 72 had a J-pouch reservoir. There were no deaths. After surgery, three children had intraabdominal sepsis and one had pelvic sepsis, but it did not lead to excision of the IAA. The mean stool frequency in all 114 patients was 5.0 +/- 2.5 per day and 1.2 +/- 1.1 at night. The mean number of stools for the straight IAA was 6 per day and 2.1 at night. The mean number of stools for the straight IAA with balloon dilations was 5.8 per day and 1.2 at night, and for the J pouch it was 4 per day and 1 at night. Patients with both the J pouch and straight IAA had good to excellent sensation, with patients with the J pouch always able to distinguish flatus from stool in 87% of patients and almost always in 13%. Daytime continence was very good in both groups. Moderate nighttime loss of stool occurred in 10 patients, 6 with a straight IAA and 4 with a J pouch. Ninety-five percent of the 114 patients were satisfied or very satisfied, with most children with a J pouch very satisfied. The J pouch remains the procedure of choice in young people.

Adolescent↗
PubMed1989

Structure, organization, and expression of the rat cardiac myosin light chain-2 gene. Identification of a 250-base pair fragment which confers cardiac-specific expression.

The present study characterized the structure, organization, and expression of the rat cardiac myosin light chain (MLC) -2 gene. The rat cardiac MLC-2 gene has seven exons which display complete conservation with the exon structure of the rat fast twitch skeletal MLC-2 gene. A 250-base pair (bp) sequence of the 5'-flanking region contains CArG motifs and additional cis elements, each greater than 10 bp in length, which were conserved in sequence and relative position with the chick cardiac MLC-2 gene. A series of MLC-2/luciferase fusion genes consisting of nested 5' deletions of the MLC-2 5'-flanking region were constructed and transfected into primary neonatal rat myocardial cells and a non-myocardial cell line (CV-1), demonstrating that this 250 bp of the MLC-2 5'-flanking region was sufficient to confer cardiac specific expression on a luciferase reporter gene. This study suggests the presence of important proximal regulatory sequences in the MLC-2 5'-flanking region which are capable of directing the cardiac specific expression of the rat cardiac myosin light chain-2 gene.

Amino Acid Sequence↗
PubMed1989

Depression and Alzheimer's disease.

In his classic case, Alzheimer described cognitive symptoms such as amnesia, aphasia, and apraxia and noncognitive symptoms such as delusions and agitation. Recent studies have suggested that depression also occurs in Alzheimer's disease. In this study, 144 patients who met criteria for Alzheimer's disease were examined for depression on a modified version of the Present State Examination. The prevalence rate of major depression was 17%. The depressed Alzheimer's disease patients were more cognitively impaired and more disabled than the nondepressed patients. Studies are needed to clarify the etiology and treatment of depression in Alzheimer's disease.

Aged↗
PubMed1988

Semantic activation and implicit memory in Alzheimer disease.

Patients with Alzheimer disease (AD) invariably display pronounced deficits in verbal memory when retention is tested explicitly. The present study examined the possibility that tasks which require memory only implicitly would be performed normally. Moderately demented patients with probable AD were severely impaired in free recall of a word list. On a subsequent word association test, the AD patients were less likely than normals to give items from the recall list as their word associations. The results suggest that implicit verbal memory, as well as explicit memory, is impaired in AD. While the magnitude of the activation effect was significantly reduced in AD patients, it was uncorrelated with recall performance or a measure of global cognitive functioning. Memory activation may thus depend on neural circuitry outside the traditional (i.e. temporo-limbic) memory system.

Aged↗
PubMed1988

Distribution of membrane proteins in mechanically dissociated retinal rods.

Solitary rods were isolated from frog retinas by mechanical dissociation. Typically, the rods cleave sclerad to the nucleus and consist of outer segments with attached partial inner segments with either tapered or rounded profiles. Light and electron microscopy reveal that the outer and inner segments of rods with tapered inner segments, like rods in the intact retina, are joined by a single connecting cilium. In contrast, the outer and inner segments of rods with rounded inner segments are fused, with no extracellular cleft between the two segments. Opsin distribution was studied in both unfused and fused rods by light and electron microscopic immunocytochemistry. Extensive surface labeling is restricted to the outer segments of tapered rods, as observed in vivo. In contrast, both inner and outer segments of rods with rounded inner segments (fused) label heavily with anti-opsin. Thus opsin, a mobile membrane protein, diffuses from the outer to the inner segment of fused rods. Segregated distribution of opsin in unfused rods suggests that the connecting cilium and/or its associated structures may normally act as a diffusion barrier between the outer and inner segments to mobile membrane proteins such as opsin. Immunofluorescence studies demonstrate that Na+/K+ ATPase is restricted in distribution to the inner segment and calycal processes of both fused and unfused isolated rods, as observed in vivo. Maintenance of its restricted distribution in fused cells indicates that Na+/K+ ATPase is not mobile and may be tethered in the surface membrane of the inner segment.

Animals↗
PubMed1988

Office management of urinary stomas.

The postoperative care of stoma patients is truly life long. With the excellent stoma equipment available, no patient should be a "stoma cripple." New advances in continent reservoirs will improve patient acceptance and lessen the fear associated with stomas. Finally, close follow-up by both the enterostomal therapy nurse and the surgeon is essential for the complete care of the stoma patient.

Ambulatory Care↗
PubMed1986

Ultrastructure of aesthetasc innervation and external morphology of the lateral antennule setae of the spiny lobster Panulirus interruptus (Randall).

Six types of setae and one type of cuticular depression were examined on the lateral antennule of the spiny lobster Panulirus interruptus using scanning electron microscopy. The organization and ultrastructure of the innervation of the most numerous setal type, the aesthetasc, were investigated using light- and transmission electron microscopy. Each aesthetasc is innervated by approximately 300 bipolar neurons whose sensory dendrites penetrate the hair and extend toward the tip, and whose axons project towards the central nervous system. The neuronal somata and two types of glia form a cluster within the antennular lumen. The inner sheath-cell somata encircle the dendritic tract distal to the sensory somata. These cells appear to extend distal processes which wrap the dendritic tract to the base of the aesthetasc. Elongate outer sheath cells are interposed between the glia-wrapped dendritic tract and the hypodermis which underlies the antennule cuticle. A continuous investment of neural lamella separates the hypodermis, the entire cluster of somata, and sensillar nerve from the antennule lumen. The organization of the neuronal somata and their association with outer and inner sheath cells in this marine species appear similar to those of crustaceans from freshwater and terrestrial habitats.

Animals↗
PubMed1985

Current chemical concepts of acids and bases and their application to anionic ("acid") and cationic ("basic") dyes.

In biomedical studies, dyes are divided into "acid" and "basic" dyes. This classification cannot be reconciled with current chemical definitions of acids and bases. Brönsted-Lowry acids are compounds that can donate protons; bases are proton acceptors. The definition of acids and bases is independent of the electric charge, i.e. acids and bases can be neutral, anionic or cationic. Reactions between acids and bases result in formation of new acid-base pairs. Lewis acids and bases do not depend on a particular element, but are characterized by their electronic configurations. Lewis bases are electron donors; Lewis acids are electron acceptors. This classification is also unrelated to the electric charge. Lewis acids and bases interact by formation of coordinate covalent bonds. In histochemistry and histology, dyes containing -SO3-, -COO- and/or -O- groups are classified as "acid" dyes. However, such compounds are electron pair donors and hence Brönsted-Lowry and Lewis anionic bases. Dyes carrying a positive charge are termed "basic" dyes. Chemically, many cationic dyes are Lewis acids because they can add a base, e.g. OH-, acetate, halides. The hypothesis that transformation of -NH2 into ammonium groups imparts "basic" properties to dyes is untenable; ammonium groups are proton donors and hence acids. Furthermore, conversion of an amino into an ammonium group blocks a lone electron pair and the color of the dye changes drastically, e.g. from violet to green and yellow. It appears therefore highly unlikely that ammonium groups are responsible for binding of cationic ("basic") dyes. In histochemistry, it is usually not of critical importance whether anionic or cationic dyes are chemically acids or bases.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗
PubMed1985

Fever in infants less than two months of age: spectrum of disease and predictors of outcome.

Four hundred thirty-four febrile infants two months of age or younger were evaluated in the emergency departments of five major teaching hospitals over a one-year period. A culture-proven bacterial infection was present in 3.5% of the infants; bacteremia was detected in 3.3%. Bacterial meningitis was present in 2.4%, and aseptic meningitis was noted in 13.4%. Twenty-one percent had clinically apparent serious disease including pneumonia, otitis media, and gastroenteritis with dehydration. Six variables (age less than 1 month, lethargy, no contact with an ill individual, breast-feeding, total polymorphonuclear greater than or equal to 10,000/mm3 and band count greater than or equal to 500/mm3) were correlated with bacterial infection by step-wise discriminant analysis. However, these findings were neither sensitive nor specific enough to be clinically useful. Management varied, and 62% of the infants were hospitalized. Fifty-four percent, some of whom were managed as outpatients, received antibiotics. Febrile infants two months of age or younger require a comprehensive emergency department assessment, including appropriate laboratory studies (CBC, differential, urinalysis and culture, lumbar puncture, and blood culture), since 3.5% have bacterial infection that may be life-threatening. Hospitalization is warranted if the infant appears ill, laboratory studies indicate serious infection, or follow-up care is uncertain.

Anti-Bacterial Agents↗