Search PubMed⌕ Search

Biomedical subjects

R J Baker

Publications and source records attributed to R J Baker.

At least 19 recordsLinked to original sources
PubMed1995

Esophageal submucosal gland duct adenoma.

An 81-year-old man with a 3-year history of dysphagia underwent endoscopic resection of a 1-cm-diameter distal esophageal mass. Examination revealed a submucosal neoplasm with a circumscribed growth pattern composed of tubules, cysts, and papillae in association with a marked interstitial lymphoid infiltrate. The cyst lumens and papillae were lined by two to six layers of cytologically bland cuboidal to columnar cells with rare mitotic figures. The basal layer of cells was uniformly positive for smooth-muscle actin. Mucin-positive intracytoplasmic lumens were focally present, but cytoplasmic mucin was not seen. There was no evidence of Barrett's metaplastic epithelium. These features are similar to those in two, possibly three, previously reported cases of esophageal adenomas and bear a resemblance to sialadenoma papilliferum, a rare neoplasm of the minor salivary glands. Their clinicopathologic and immunohistologic features suggest that these neoplasms derive from the submucosal gland ducts. Comparison with the previously reported cases indicates that although the proportions of the various components (tubules, cysts, and papillae) may vary, all cases appear to pursue a slowly growing, clinically indolent course with no evidence of recurrence after complete resection.

Actins↗
PubMed1992

Transposable elements and the evolution of genome organization in mammals.

All mammalian transposable elements characterized to date appear to be nonrandomly distributed in the mammalian genome. While no element has been found to be exclusively restricted in its chromosomal location, LINE elements and some retrovirus-like elements are preferentially accumulated in G-banding regions of the chromosomes, and in some cases in the sex chromosomes, while SINE elements occur preferentially in R-banding regions. Four mechanisms are presented which may explain the nonrandom genomic distribution of mammalian transposons: i) sequence-specific insertion, ii) S-phase insertion, iii) ectopic excision, and iv) recombinational editing. Some of the available data are consistent with each of these four models, but no single model is sufficient to explain all of the existing data.

Animals↗
PubMed1992

Restriction endonuclease digestion patterns of harvest mice (Reithrodontomys) chromosomes: a comparison to G-bands, C-bands, and in situ hybridization.

Constitutive heterochromatin of a karyotypically conserved species of harvest mouse was compared to that of three karyotypically derived species of harvest mice by examining banding patterns produced on metaphase patterns produced by two of these restriction endonucleases (EcoRI and MboI) were compared to published G- and C-banded karyotypes and in situ hybridization of a satellite DNA repeat for these taxa. The third restriction endonuclease (PstI) did not produce a detectable pattern of digestion. For the most part, patterns produced by EcoRI and MboI can be related to C-banded chromosomes and in situ hybridization of satellite DNA sequences. Moreover, digestion with EcoRI reveals bands not apparent with these other techniques, suggesting that restriction endonuclease digestion of metaphase chromosomes may provide additional insight into the structure and organization of metaphase chromosomes. The patterns produced by restriction endonuclease digestion are compatible with the chromosomal evolution of these taxa, documenting that in the highly derived taxa not only are the chromosomes rearranged but the abundance of certain sequences is highly variable. However, technical variation and difficulty in producing consistent results even on a single slide with some restriction endonucleases documents the problems associated with this method.

Animals↗
PubMed1991

Phylogenetic relationships among megabats, microbats, and primates.

We present 744 nucleotide base positions from the mitochondrial 12S rRNA gene and 236 base positions from the mitochondrial cytochrome oxidase subunit I gene for a microbat, Brachyphylla cavernarum, and a megabat, Pteropus capestratus, in phylogenetic analyses with homologous DNA sequences from Homo sapiens, Mus musculus (house mouse), and Gallus gallus (chicken). We use information on evolutionary rate differences for different types of sequence change to establish phylogenetic character weights, and we consider alternative rRNA alignment strategies in finding that this mtDNA data set clearly supports bat monophyly. This result is found despite variations in outgroup used, gap coding scheme, and order of input for DNA sequences in multiple alignment bouts. These findings are congruent with morphological characters including details of wing structure as well as cladistic analyses of amino acid sequences for three globin genes and indicate that neurological similarities between megabats and primates are due to either retention of primitive characters or to convergent evolution rather than to inheritance from a common ancestor. This finding also indicates a single origin for flight among mammals.

Amino Acid Sequence↗
PubMed1991

Evidence for biased gene conversion in concerted evolution of ribosomal DNA.

Concerted evolution is the production and maintenance of homogeneity within repeated families of DNA. Two mechanisms--unequal crossing over and biased gene conversion--have been the principal explanations of concerted evolution. Concerted evolution of ribosomal DNA (rDNA) arrays is thought to be largely the result of unequal crossing over. However, concerted evolution of rDNA in parthenogenetic lizards of hybrid origin is strongly biased toward one of two parental sequences, which is consistent with biased gene conversion as the operative mechanism. The apparent gene conversions are independent of initial genome dosage and result in homogenization of rDNA arrays across all nucleolar organizer regions.

Animals↗
PubMed1991

IBEES Prize Lecture. The future of biomedical engineering.

Biomedical engineering is recognized as having developed an identity distinct from traditional engineering disciplines. The concepts which characterize this identity are outlined. The consequences of these are considered with particular attention to changing attitudes to professional specialization and work within the clinical environment.

Awards and Prizes↗
PubMed1991

Use of technetium-99m(V)thiocyanate to measure gastric emptying of fat.

Technetium-99m(V)thiocyanate was evaluated as a radio-pharmaceutical for measuring gastric emptying of fat. Olive oil was labeled with 99mTc(V)thiocyanate by direct extraction from acidic thiocyanate solution. After incubation with dilute HCl (pH 1.4) at 37 degrees C for 3 hr, approximately 5% of the total radioactivity eluted into the aqueous phase. When incubated with human gastric juice (pH 1.8 and 2.2), approximately 8% of the activity was detected in the aqueous phase at 3 hr. Scintigraphic studies performed in two rabbits showed that olive oil labeled with 99mTc(V)thiocyanate emptied slowly from the stomach, with a gastric half-emptying time (T50) of more than 3 hr. A low-nutrient soup labeled with 113mIn-DTPA and mixed with 99mTc(V)thiocyanate labeled oil was consumed by six human volunteers. The oil emptied much more slowly (p less than 0.02) (median T50 = 198 min) than the aqueous component (median T50 = 30 min). These observations indicate that 99mTc(V)thiocyanate is a suitable pharmaceutical to measure gastric emptying of extracellular fat.

Adult↗
PubMed1990

Intragenomic movement, sequence amplification and concerted evolution in satellite DNA in harvest mice, Reithrodontomys: evidence from in situ hybridization.

Three DNA probes isolated from three species of Reithrodontomys (R. montanus, R. megalotis, R. fulvescens) were used to examine within and among species variation in the chromosomal location of satellite DNA and constitutive heterochromatin. These probes hybridized to the centromeric regions on all chromosomes in six species of the subgenus Reithrodontomys. Additionally, nearly all extra-centromeric C-band positive regions (with the exception of some heterochromatic material on the X and Y) hybridized to these probes. Within the subgenus Reithrodontomys both the chromosomal distribution and organization of satellite DNA has changed throughout evolution. The evolutionary transition has been from a totally centromeric position in R. fulvescens to centromeric and non-centromeric regions in other species that have undergone extensive chromosomal rearrangements from the primitive karyotype for peromyscine rodents. In addition, the monomer repeat of the satellite sequence differs between R. fulvescens (monomer defined by PstI) and the remaining species in the subgenus Reithrodontomys (monomer defined by EcoRI). These results suggest at least two amplification events for this satellite DNA sequence. Models and mechanisms concerned with the homogenization and spread of satellite sequences in complex genomes are evaluated in light of the Reithrodontomys data. From a phylogenetic standpoint, the satellite sequences composing heterochromatic regions were restricted to the subgenus Reithrodontomys, which supports morphological differences used to recognize two subgenera, Reithrodontomys and Aporodon. Probes failed to hybridize to any part of the karyotype of R. mexicanus (subgenus Aporodon) or to seven species from other closely related genera (Baiomys, Neotoma, Nyctomys, Ochrotomys, Onychomys, Peromyscus, Xenomys), some of which are considered as potential sister taxa for Reithrodontomys.

Animals↗
PubMed1990

Distribution of non-telomeric sites of the (TTAGGG)n telomeric sequence in vertebrate chromosomes.

The intrachromosomal distribution of non-telomeric sites of the (TTAGGG)n telomeric repeat was determined for 100 vertebrate species. The most common non-telomeric location of this sequence was in the pericentric regions of chromosomes. A variety of species showed relatively large amounts of this sequence present within regions of constitutive heterochromatin. We discuss possible relationships between the non-telomeric distribution of the (TTAGGG)n sequence and the process of karyotype evolution, during which these sites may provide potential new telomeres.

Amphibians↗
PubMed1990

Genetic variation and origin of the most chromosomally polymorphic natural mammalian population.

Examination of allozymic variation in a chromosomally highly polymorphic population of Oryzomys documented that the sample consisted of two species, one that was chromosomally monomorphic and the other containing nine centric fusion polymorphisms. The existence of allozymic variation indicates that it is highly improbable that the polymorphic sample was the result of hybridization. These centric fusion polymorphisms appeared to cause little or no negative selection.

Alleles↗
PubMed1990

Kit preparation of technetium-99m-mercaptoacetyltriglycine: analysis, biodistribution and comparison with technetium-99m-DTPA in patients with impaired renal function.

Technetium-99m-mercaptoacetyltriglycine (99mTc-MAG3) was prepared by a frozen solution method, enabling the preparation of kits yielding a product substantially free of lipophilic impurities (96% 99mTc-MAG3). However, biliary activity was not completely eliminated as HPLC-purified 99mTc-MAG3 was also excreted by that route. Sequential 99mTc-DTPA and 99mTc-MAG3 renal scans were performed in 15 patients with renal dysfunction, including renal transplant recipients. In all cases, the 99mTc-MAG3 kit preparation provided superior images to 99mTc-DTPA at all levels of renal function due to a higher target-to-background ratio and a plasma clearance twice as fast as 99mTc-DTPA. Interpretation of delayed 99mTc-MAG3 images, however, was complicated by biliary excretion which will limit quantitative estimates of renal clearance. A 99mTc-MAG3 kit is likely to be of value in renal transplant assessment and in cases of significant renal impairment but would not appear to offer major advantages over 99mTc-DTPA in routine renal imaging.

Chromatography, High Pressure Liquid↗
PubMed1988

Evidence for eight tandem and five centric fusions in the evolution of the karyotype of Aethomys namaquensis A. Smith (Rodentia: Muridae).

G- and C-banded chromosomes of Aethomys namaquensis (2n = 24), A. chrysophilus (2n = 44), and Praomys coucha (2n = 36) are compared and contrasted with published material on Australian Muridae and North American Sigmodontidae. Direction and types of chromosomal rearrangements are established using cladistic methodology. An acrocentric morphology for chromosomes 5, 14, 15 and 20 (numbering system from Peromyscus) are proposed as primitive for the common ancestor of the Muridae and Sigmodontidae rodent lineages. Reduced diploid number of Aethomys namaquensis is derived by eight tandem and five centric fusions since divergence from the common ancestor with A. chrysophilus. The two species of Aethomys share one derived metacentric chromosome that distinguishes them from Praomys. Praomys has unique chromosomes which can be derived from the proposed primitive condition by five centric fusions and five pericentric inversions. It is concluded that karyotypic orthoselection for tandem and centric fusions is best explained by cellular or biochemical mechanisms rather than variation in population characteristics.

Animals↗
PubMed1988

Electrophoretic and immunoelectrophoretic analysis of feline serum proteins.

Serum from 28 clinically healthy cats was subjected to agarose gel electrophoresis and the migration distance relative to albumin was determined. The reference values for the relative and absolute concentrations of each protein fraction were determined and compared to previous reports. The immunoelectrophoretic, crossed immunoelectrophoretic and crossed line immunoelectrophoretic pattern, of a pooled sample of serum from clinically normal cats was determined. The cross-reactivity between goat and/or rabbit monospecific antisera to human proteins and feline serum was determined using immunoelectrophoresis and crossed-line absorption immunoelectrophoresis. Feline alpha-2-macroglobulin, haptoglobin, B1C-globulin, IgG, albumin and ceruloplasmin cross reacted strongly with the monospecific antisera. Alpha-2-macroglobulin migrated anodal to haptoglobin. Lipoproteins and ceruloplasmin were studied using staining procedures described in man. Feline transferrin was precipitated with Rivanol.

Animals↗
PubMed1988

Myelolipoma and endocrine dysfunction.

Myelolipoma is an uncommon benign tumor of which the pathogenesis is unknown. It is rarely associated with endocrine disorders. We present a case of a myelolipoma in conjunction with congenital adrenal hyperplasia secondary to 21-hydroxylase deficiency. Nine previously reported cases of myelolipoma associated with endocrine dysfunction are reviewed with potential correlation of the hormonal imbalance to pathogenesis.

Adrenal Gland Neoplasms↗