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Biomedical subjects

E Roberts

Publications and source records attributed to E Roberts.

At least 109 records · Page 6Linked to original sources
PubMed1994

An amyloid beta-protein fragment, A beta[12-28], equipotently impairs post-training memory processing when injected into different limbic system structures.

Previously, amyloid beta-protein (A beta) fragments 1-28, 12-28 and 12-20 were found to impair retention in mice when injected intracerebroventricularly after footshock active avoidance training. We now have measured the dose-dependence of amnestic effects of peptide 12-28 stereotactically injected into amygdala, caudate, hippocampus, mammillary bodies and septum, which limbic structures are known to be involved in memory processing and into the medial thalamus, which largely is involved in sensory processing during training. Peptide 12-28 impaired retention with remarkably similar efficacy when injected into limbic structures but was not at all amnestic upon thalamic injection. Present results together with those in the literature lead us to suggest that A beta may exert dysregulatory cognitive effects by incoordination of K(+)-channel function in neurons, glia and endothelial cells.

Amino Acid Sequence↗
PubMed1994

Different active sites of mammalian DNA ligases I and II.

Bovine DNA ligases I and II were adenylylated in the presence of [alpha-32P]ATP and digested with limiting amounts of trypsin or V8 protease. The generation of radioactive peptides of decreasing size was monitored by polyacrylamide gel electrophoresis and autoradiography. Active site peptides obtained by complete proteolytic digestions with trypsin, V8, or Lys-C protease were also compared. The partial digestion products of DNA ligases I and II were entirely different, with no indication of extensive sequence homology. Furthermore, the sequence of the active site region of DNA ligase I is clearly different from that of DNA ligase II. Similar analysis of a third chromatographically distinct mammalian DNA ligase indicated that it is different from DNA ligase I but related to DNA ligase II.

Adenosine Monophosphate↗
PubMed1994

Topography of a binding site for small amnestic peptides deduced from structure-activity studies: relation to amnestic effect of amyloid beta protein.

Four peptides homologous to amyloid beta protein containing the Val-Phe-Phe (VFF) sequence administered intracerebroventricularly after training caused amnesia for footshock active avoidance training in mice. Results with VFF and other peptides containing VFF or portions thereof were used to generate a topographic map for a hypothetical binding surface for amnestic peptides, termed Z. Effects on retention of footshock active avoidance training were rationalized in terms of fit to Z, making possible design of potential memory-modulating peptidic and nonpeptidic substances. Three peptides that neither improved nor impaired retention blocked the amnestic effects of beta-(12-28), a peptide homologous to amyloid beta protein, opening the way to development of substances that can antagonize the neurotoxic effects of amyloid beta protein on neural structures and thus attenuate symptoms and progression of Alzheimer disease.

Amino Acid Sequence↗
PubMed1994

Effects of thyroxine and its related compounds on cerebral GABA receptors: inhibitory action on benzodiazepine recognition site in GABAA receptor complex.

The effects of thyroxine and its related derivatives on gamma-aminobutyric acid (GABA) receptors in the rat brain were examined. D-Thyroxine strongly inhibited [3H]flunitrazepam binding to benzodiazepine receptor in crude synaptic membrane from the rat brain. The Scatchard analysis of the [3H]flunitrazepam binding in the presence of D-thyroxine indicated the decreases in the affinity and maximum number of binding site. Furthermore, D-thyroxine inhibited the enhancing effect of flunitrazepam on GABA-stimulated 36Cl- influx into membrane vesicles, although GABA-stimulated 36Cl- influx alone was not affected by D-thyroxine. On the other hand, the effects of thyroxine and its related derivatives on cerebral GABAB receptor binding were not noted. These results suggest that D-thyroxine may be a drug which is able to modulate the function of GABAA receptor complex via the inhibitory action on benzodiazepine recognition site.

Animals↗
PubMed1994

The gene for Darier's disease maps between D12S78 and D12S79.

Darier's disease is a dominantly inherited skin disorder in which there is abnormal adhesion between keratinocytes. We and others have recently mapped the disease gene to chromosome 12q23-q 24.1. In the present study we have established that the disease gene lies between the loci D12S78 and D12S79 which are 12cM apart. We have also obtained direct evidence that the disease is unlikely to result from a mutation in one of the members of the keratin gene cluster on chromosome 12q.

Chromosome Mapping↗
PubMed1994

Feedback on quality: patients' experience of surgical care.

There is a growing consensus within the NHS of the importance of obtaining feedback from patients in order to improve the quality of health care; consequently, many patient satisfaction surveys are now undertaken. However, much research is based on provider-held assumptions about service quality. This study focuses on patient satisfaction with coronary bypass surgery, starting with the concerns expressed by patients and using these as a basis for evaluating different aspects of care. The paired comparison technique was employed to produce a ranked list of aspects of care that were perceived to be in greatest need of improvement. Some difficulties were encountered in administering the ranking technique to patients in a highly specialized health-care setting; however, results were obtained and validated for follow-up patients. The item of most concern to these patients was a lack of sensitivity about when patients felt ready for discharge.

Coronary Artery Bypass↗
PubMed1994

Constipation and reversible urinary tract abnormalities.

Urinary tract anomalies were prospectively investigated with ultrasound in 29 children with functional constipation. These children were compared before and after treatment with 451 age matched healthy controls without constipation. The bladder residue and upper renal tract dilatation after micturition were significantly increased in the group with constipation and improved after treatment.

Adolescent↗
PubMed1994

The regulation of DNA topoisomerase II by casein kinase II.

DNA topoisomerase II is an essential nuclear enzyme required for the proper condensation and segregation of chromosomes during mitotic and meiotic cell division. The enzyme exists in the cell as a phosphoprotein, and it is most highly phosphorylated in G2 and M-phases of the cell cycle. We have shown that topoisomerase II is the target of casein kinase II (CKII) in yeast by comparison of in vivo and in vitro phosphotryptic peptide maps. Limited proteolysis and probing with domain specific antibodies show that with the exception of a weakly modified residue between aa 660 and aa 1250, all residues modified by CKII are in the last 200 amino acids of yeast topoisomerase II. This C-terminal domain is the least conserved region of the enzyme and truncation of the enzyme shows that it is nonessential for activity in vitro. However, the fully dephosphorylated full-size protein is nearly inactive in decatenation assays, and activity can be restored by phosphorylation by CKII. To reconcile these observations, we propose that the C-terminal region is a negative regulatory domain, counteracted by phosphorylation within the domain itself. To test this hypothesis we have mutagenised 12 potential CKII phosphoacceptor sites in the C-terminus of topoisomerase II and introduced the mutant genes into a yeast strain which has a temperature sensitive top2 gene. The growth of the transformed strains is monitored at nonpermissive temperature to determine whether C-terminal phosphorylation is important for mitotic growth. In addition, we have purified the mutant enzymes to homogeneity for in vitro assays.

Amino Acid Sequence↗
PubMed1993

Further characterization of the D2 dopamine receptor expressed in MMQ cells.

The D2 dopamine receptor expressed in the MMQ cell line was characterized by saturation binding using the D2 dopamine radioligand [3H]spiperone. The KD for spiperone was 41 pM and the Bmax for these sites was 34 fmol/mg protein. Inhibition of forskolin-stimulated cAMP accumulation occurred in response to a variety of D2 agonists, and the agonist effects were reversed by D2 antagonists. Pertussis toxin pretreatment abolished agonist inhibition of cAMP accumulation. In addition, the alpha 2-adrenergic agonist UK 14304 inhibited cAMP accumulation; this effect was reversed by an alpha 2-adrenergic antagonist but not by a D2 antagonist, indicating the presence of alpha 2-adrenergic receptors on these cells. Specific oligonucleotide primers were used in the polymerase chain reaction to determine, by restriction enzyme analysis and Southern blotting, that the long form of the two alternatively spliced variants of the D2 dopamine receptor was the predominant variant expressed in these cells.

Animals↗
PubMed1993

A pump-pore model for transmembrane transport of hydrophilic solutes.

Transmembrane transport of a hydrophilic solute is presumed to begin when hydrated ligand adheres in Velcro-like fashion to hydrated membrane surface. Asymmetric physical forces cause rolling movements of ligand over membrane surface until contact occurs with appropriate transport machinery, consisting of a pump (Pu) to which is tethered a ligand (Li)-specific perm-selective pore (Po). The Po is in the open form when the Li is attached to an external high-affinity allosteric site on it. The active form of the Pu is stabilized by attachment of the Li to high-affinity internal or low-affinity external allosteric sites. The active form of the Pu induces closure of the Po, even when ligand is bound to it; the inactive conformation of the Pu permits Po opening. Attachment of Li to either one of two binding sites on the active Pu and irreversible envelopment by it in Venus fly-trap fashion trigger transmembrane transport of Li. Multistep attachment of Li is rate-limiting in the transport process. Application of a simple equation derived from relevant kinetic considerations relating velocity of transport (V) to concentration of Li (L), V = k1(L)1/2, gives V-L curves approximating transport data obtained in a variety of biological systems. This model is congruent with the ability of cells to concentrate substances from extremely dilute solutions and with the adaptive informational value to cells of rates of transport.

Animals↗
PubMed1993

Cholecystokinin dipeptoid antagonists: design, synthesis, and anxiolytic profile of some novel CCK-A and CCK-B selective and "mixed" CCK-A/CCK-B antagonists.

The design, synthesis, and structure-activity relationships (SAR) for the development of selective dipeptoid ligands for both of the cholecystokinin (CCK) receptor subtypes CCK-A and CCK-B are described. The SAR developed is used to design a ligand with equal nanomolar binding affinity for both the CCK-A and CCK-B receptors. Example compounds such as [1R-[1 alpha[R*(R*)],2 beta]]-4-[[2-[[3-(1H-indol-3-yl)- 2-methyl-2-[[[(2-methylcyclohexyl)oxy]carbonyl]amino]-1- oxopropyl]-amino]-1-phenylethyl]amino]-4-oxo-butanoic acid (24c), (1R-trans)-N-[alpha-methyl-N-[[(2-methylcyclohexyl)oxy] carbonyl]-D-tryptophyl]-L-3-(phenylmethyl)-beta-alanine (28i), and N-[alpha-methyl-N-[(tricyclo[3.3.1.1]dec-2-yloxy) carbonyl]-D-tryptophanyl]-L-3-(phenylmethyl)-beta-alanine (30m) are CCK-B selective compounds having CCK-B binding affinities of IC50 = 3.9, 0.34, and 0.15 nM with a CCK-A/CCK-B ratio of 464, 53, and 170, respectively. Other compounds such as (1R-trans)-N-[alpha-methyl-N-[[(2-methylcyclohexyl)oxy]carbonyl]- L-tryptophyl]-D-3-(phenylmethyl)-beta-alanine (281) and N-(alpha-methyl-N-[(tricyclo[3.3.1.1]dec-2-yloxy)carbonyl]-L - tryptophyl]-D-3-(phenylmethyl)-beta-alanine (30p) are CCK-A-selective compounds having CCK-A binding affinities of IC50 = 7.9 and 2.82 nM with a CCK-A/CCK-B ratio of 0.007 and 0.01, respectively. Further to these, (1S-trans)-N-[alpha-methyl-N-[[(2-methylcyclohexyl)oxy] carbonyl]-D-tryptophyl]-L-3-(phenylmethyl)-beta-alanine (28h) is a mixed CCK-A/CCK-B ligand with a CCK-A binding affinity of IC50 = 3.9 nM and a CCK-B binding affinity of IC50 = 4.2, producing a CCK-A/CCK-B ratio of unity. The CCK-B selective compounds are shown to be antagonists in electrophysiological tests on the rat ventromedial nucleus of the hypothalamus with an equilibrium constant (Ke) value of 2.8 nM for 30m and are also shown to be anxiolytic in the mouse ligh/dark box test with a minimum effective dose of 0.01 mg/kg, sc, for 30m. The CCK-A selective compounds are also shown to be competitive antagonists by the inhibition of CCK-8S-evoked amylase secretion from pancreatic acinar cells with a Ke value of 16 nM for 30p. In electrophysiological tests on the rat dorsal raphé (an area rich in CCK-A receptors) 30p had a Ke value of 12.8 nM. The mixed CCK-A/CCK-B compound 28h showed antagonistic properties in both CCK-A and CCK-B models; thus it inhibited CCK-8S-evoked amylase secretion from pancreatic acinar cells and is anxiolytic in the light/dark box paradigm.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1993

GABA--the quintessential neurotransmitter: electroneutrality, fidelity, specificity, and a model for the ligand binding site of GABAA receptors.

Alone of the known neurotransmitters, GABA is an electroneutral zwitterion (pI = 7.3) at physiological pH. This confers the highest probability of successfully traversing densely packed synaptic gaps without interacting electrostatically with charged entities enroute, making GABA a high fidelity neurotransmitter. Inhibitory tone in the nervous system is coordinately coupled with physiological activity by means of the GABA system, acidification increasing GABA formation and its Cl- channel-opening efficacy, while decreasing its removal by transport and metabolic degradation. The above, together with diminution upon acidification of the postsynaptic efficacy of glutamate on excitatory NMDA receptors constitutes a sensitively responsive mechanism by which protons control levels of neural activity, locally and globally. A model made of the GABA binding site of GABAA receptors based on H-bond and hydrophobic interactions makes it seem unlikely that any other substance known to occur in nerve tissue would give rise to a high noise level at GABAA receptors.

Animals↗
PubMed1993

Cytotoxicity of aluminum silicates in primary neuronal cultures.

To study their cytotoxicity, clays containing aluminum silicates were added to cultures of primary murine spinal cord neurons and differentiated N1E-115 neuroblastoma cells. Bentonite (0.1 mg/ml) and montmorillonite (0.1 mg/ml) rapidly associated with the outer membrane of both N1E-115 and neuronal cells. Erionite (0.1 mg/ml) was randomly distributed throughout the culture. Both bentonite and montmorillonite caused complete cell lysis in the neuronal cultures within 60 min following addition. Erionite had no effect. None of the clays appeared to be cytotoxic to the differentiated N1E-115 cells even though bentonite and montmorillonite were closely associated with the cell membrane. N1E-115 cell lysis did not occur up to 18 h after addition of the clay. Aluminum silicate-containing clays caused a rapid lysis of primary neuronal cells. Differentiated N1E-115 neuroblastoma cells were not susceptible to clay-induced lysis, suggesting that the lytic mechanism is not a general phenomenon that affects all cell types equally.

Aluminum Silicates↗
PubMed1993

Aluminum silicate toxicity in cell cultures.

To assess the cytotoxicity of four clays containing an aluminum silicate--montmorillonite, bentonite, kaolinite and erionite--we used human umbilical vein endothelial, N1E-115 neuroblastoma, and ROC-1 oligodendroglial cells. Morphological examination, lactate dehydrogenase release and fatty acid release were used as indices of trauma. The clays were added in suspension to the cell cultures at concentrations of 0.1, 0.03 and 0.01 mg/ml of medium and the cells were incubated for 1, 6 and 24 h. The clays did not lyse ROC-1 and N1E-115 cells and did not cause a dose-dependent increase in fatty acid levels at 24 h. There were no significant increases in lactate dehydrogenase activity in N1E-115 neuroblastoma or ROC-1 oligodendroglial cells. In human umbilical vein endothelial cells, montmorillonite, kaolinite and bentonite caused a dose-dependent increase in fatty acids at 24 h. All three clays caused cell lysis. We postulate that the cytotoxicity of the clays containing an aluminum silicate towards endothelial cells may disrupt the blood-brain barrier in the affected areas, allowing the entry of the clay particle into the brain. Aluminum silicate clays caused a dose-dependent release of fatty acids in human umbilical vein endothelial cells. The clays also caused lysis of these cells. ROC-1 oligodendroglia and N1E-115 neuroblastoma cells were not lysed by the clays, suggesting that this is not a general phenomenon.

Aluminum Silicates↗
PubMed1993

Conformationally restricted analogues of the potent CCK-B antagonist CI-988.

The synthesis and structure-activity relationships (SAR) for a series of conformationally restricted analogues of the selective cholecystokinin (CCK) antagonist CI-988 and some closely related analogues are described. A series of appropriately substituted cis- and trans-amino decalins are prepared that mimic the through bond distances between the functional groups in the parent compound CI-988 whilst restricting bond rotation. This strategy has led to conformationally more rigid derivatives that have increased CCK-B receptor binding affinity.

Animals↗