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Biomedical subjects

N Walker

Publications and source records attributed to N Walker.

At least 109 records · Page 6Linked to original sources
PubMed1986

Nucleolar canalicular structure in extrauterine endometriosis.

Under the influence of progesterone the unique intranuclear structure known as the nucleolar canalicular structure (NCS) develops in the human endometrium. This organelle was not described previously outside the uterus. In this report the cases of two patients in whom the NCS appeared in extrauterine endometriosis are presented.

Adult↗
PubMed1985

Isolation of the gene encoding adenylate cyclase in Saccharomyces cerevisiae.

By complementation of the cyr1-1 mutation in Saccharomyces cerevisiae, we have isolated yeast genomic DNA containing the structural gene that encodes the catalytic unit of adenylate cyclase (EC 4.6.1.1). The isolated DNA restored adenylate cyclase activity to cyr1-1 mutants and directed integration at the CYR1 locus. Wild-type strains transformed with CYR1 DNA on the high copy number vector YEp24 contained 4- to 6-fold more adenylate cyclase activity than strains carrying the plasmid with no insert. This result suggests that expression of the CYR1 gene product, rather than that of other polypeptide components of the adenylate cyclase system, limits total adenylate cyclase activity in S. cerevisiae. CYR1-containing plasmids also complemented the temperature-sensitive growth defect of the cell division cycle mutation cdc35-1, which confers a phenotype under restrictive conditions similar to that of cyr1-1 and maps to the same locus. Further, cdc35-1 cam mutants, which contain mutations that enable them to take up cAMP from the medium, grew at the restrictive temperature in the presence of exogenous cAMP. These observations support the view that CDC35 and CYR1 are allelic and confirm the hypothesis that cAMP synthesis is required for cells to pass through the "start" position of the cell division cycle.

Adenylyl Cyclases↗
PubMed1985

[Diagnosis and therapy of the narrow lumbar spinal canal].

In 30%-40% of the patients who are operated on for herniation of lumbar discs, osseous stenosis plays a certain role. However, only in one-third of them are special operative measures such as laminectomy necessary with or without additional lumbar fusion. When spondylodesis is carried out after laminectomy it is often combined with metal implant, which can drastically reduce the time a patient requires perioperative treatment. In younger patients showing typical signs of nerve root compression due to osseous stenosis of lateral recess, only segmental decompression in the form of foraminotomy is done. On the other hand, in cases of narrow spinal canal, which is found in elderly patients, neurogenic intermittent claudication is the predominant clinical picture. Kyphosis, scoliosis, and vertebral displacement can lead to local spinal stenosis. On addition, local pressure and tension on unstabile segments in combination with secondary fibrosis can lead to compression of the neural structures. The diagnosis is based on the clinical history and myelography. Computed tomography helps reveal the presence of herniation of a lumbar disc, which should be simultaneously operated upon. For the operative treatment there is no age limit. All in all, the operative results are so good that one is inclined to decide in favour of operation.

Bone Plates↗
PubMed1984

Uterine growth responses of the mature castrate rat to estradiol-17B.

To examine estrogen-stimulated uterine growth we have monitored changes in uterine DNA synthesis, ornithine decarboxylase (ODC) activity and protein content as well as luminal epithelial (LE) cell mitotic index and ultrastructural changes. We have utilized this model to examine castrate mature rat uterine growth as a function of time between 18 and 40 hours following a single injection of 25.0 ug of estradiol-17B. LE cell mitotic index and protein content increases were maximally elevated as early as 18 hours postinjection while uterine ODC activity was maximal at 28 hours; uterine DNA synthesis increases continued throughout the experiment. In addition, the infusion of either 1 or 2 ug E2 plus progesterone over a 24 hour period, stimulated elevated ODC activity under both treatment regimens and LE cell mitotic index which was inversely related to E2 dose.

Animals↗
PubMed1983

Identification by direct photoaffinity labeling of an altered phosphodiesterase in a mutant S49 lymphoma cell.

Extracts of a mutant S49 lymphoma cell line, termed K30a, hydrolyze cAMP and cGMP at rates much faster than do wild type S49 extracts. This elevated phosphodiesterase activity, called K-PDE, elutes as a single peak of activity on DEAE-cellulose columns (Brothers, V. M., Walker, N., and Bourne, H. R. (1982) J. Biol. Chem. 257, 9349-9355). Direct photoaffinity labeling of K30a extracts with [32P]cGMP results in radiolabeling of a unique polypeptide, not observed in wild type extracts, which migrates in sodium dodecyl sulfate polyacrylamide gels with an Mr = 106,000. The 106-kDa band was identified as the catalytic K-PDE polypeptide based on the following observations: competitive inhibitors and substrates of K-PDE inhibit photolabeling of the 106-kDa band, indicating that [32P] cGMP photolabels the enzyme at its catalytic site; on DEAE-cellulose chromatography the polypeptide that is susceptible to photolabeling co-elutes with K-PDE activity; the 106-kDa band is detectable in extracts of WT X K30a hybrids (where WT denotes wild type) in amounts proportional to the K-PDE activity in the hybrids, but is undetectable in wild type. The hybrid phenotype strongly suggests that the K30a phenotype is not due to mutations that affect either a diffusible regulator of transcription or an enzyme that modifies K-PDE. Although wild type cells contain a minor cGMP phosphodiesterase activity distinct from the major cAMP phosphodiesterase, the wild type cGMP phosphodiesterase is not susceptible to radiolabeling with [32P]cGMP; this rules out the possibility that the K30a phenotype is caused by overexpression of a wild type phosphodiesterase. We conclude that the K30a mutation produced expression of a new species of phosphodiesterase molecule that is not detectably expressed in the parental S49 wild type cell line.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

A guanine nucleotide-sensitive adenylate cyclase in the yeast Saccharomyces cerevisiae.

Adenylate cyclase in particulate extracts of Saccharomyces cerevisiae utilized either MnATP or MgATP as substrate. A mutation in the CYR1 gene, which codes for the catalytic unit of yeast adenylate cyclase (Matsumoto, K., Uno, I., and Ishikawa, T. (1983) Cell 32, 417-423), eliminated utilization of both MgATP and MnATP, indicating that a single enzyme was responsible for both activities. GTP and guanylyl-5'-imidodiphosphate stimulated yeast adenylate cyclase, while a GDP analog, guanosine-5'-O-(2-thiodiphosphate), competitively inhibited this stimulation. Thermal inactivation studies distinguished putative guanine-nucleotide regulatory protein (N) from the catalytic unit (C) of yeast adenylate cyclase. Yeast N, which conferred guanine nucleotide regulation and the ability to utilize MgATP on yeast C, was quickly inactivated by incubation of particulate extracts at 30 degrees C. In contrast, yeast C, which apparently utilized MnATP as substrate in the absence of a functional N protein, resisted inactivation at 30 degrees C. These observations suggested that physically distinct protein components mediated the catalytic activity of yeast adenylate cyclase and its regulation by guanine nucleotides. These findings indicate a striking homology between the adenylate cyclase systems of S. cerevisiae and those of vertebrate cells.

Adenylyl Cyclases↗
PubMed1983

Comprehension and recall of sentences by mentally retarded and nonretarded individuals.

A cued sentence-recall task was used to determine the extent to which 24 mildly mentally retarded adolescents and 24 equal-MA nonretarded children differed in their ability to recall sentences and to infer and utilize particular exemplars of general nouns as retrieval cues. We found that the sentence recall performance of the retarded adolescents was poor relative to that of the nonretarded children; however, both groups found general and particular cues to be equally effective retrieval aids for target sentences. Differential sentence reconstruction and editing strategies were suggested as possible sources of the obtained recall differences.

Cues↗
PubMed1982

Use of categorical knowledge to aid recall.

Recall performance of 84 mildly retarded adolescents and 84 non-retarded fourth graders was compared under various encoding conditions. The seven encoding conditions consisted of the following format-cueing combinations: simultaneous-subject cues, simultaneous-experimenter cues, sort-subjects cues, sort-experimenter cues, sequential-subject cues, sequential-experimenter cues, and sequential-no cues. Stimuli were 24 colour pictures from six categories. Results indicated generally comparable levels of performance for retarded and non-retarded subjects. However, retarded subjects were less responsive to sort and experimenter cue conditions, which led to increased recall in the non-retarded subjects. It was suggested that retrieval difficulties may be interfering with the ability of retarded individuals to utilize categorical knowledge to facilitate recall.

Adolescent↗
PubMed1982

Dermatological reactions to lithium: a critical review of the literature.

This article reviews clinical reports of dermatological reactions to lithium. Such reactions include maculopapular, acneiform, and follicular eruptions, psoriasis, and other manifestations. Standard psychiatric texts offer the psychiatrist little information concerning the prevalence or seriousness of these reactions, nor do they discuss the effectiveness of various treatment alternatives. More surprisingly, most dermatology texts do not even describe skin reactions to lithium. Dermatological reactions to lithium may occur more commonly than previously documented, but with the exception of some psoriatic cases, management without the need for lithium discontinuation is usually possible.

Acne Vulgaris↗