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G Dawson

Publications and source records attributed to G Dawson.

At least 163 records · Page 9Linked to original sources
PubMed1989

Effects of dopamine receptor activation on the level of cyclic AMP in the trabecular meshwork.

We examined the effects of dopamine and of a selective DA1 agonist, fenoldopam, on the levels of cyclic AMP in the trabecular meshwork, freshly excised from porcine and canine eyes. As measured by radioimmunoassay, fenoldopam at a concentration of 10(-5) M caused a 4-fold increase in the cyclic AMP content, from a basal level of 24.4 +/- 1.9 to 101.8 +/- 6.3 pmol/mg protein, of the trabecular meshwork samples from porcine eyes. In tissue samples from canine eyes, fenoldopam at a concentration of 10(-4) M increased the endogenous cyclic AMP level from a basal value of 26.0 +/- 4.6 to 64.2 +/- 5.7 pmol/mg protein. Dopamine, although less potent, produced a similar response. Preincubation with a DA1 receptor antagonist, SCH 23390, inhibited the increase in cyclic AMP levels by 90%. Such inhibition did not occur with the alpha- and beta-receptor antagonists phenoxybenzamine and propranolol, respectively. This investigation demonstrates that adenylate cyclase-coupled DA1 receptors are present in porcine and canine trabecular meshwork tissue.

Animals↗
PubMed1988

Cholera toxin discriminates between murine T lymphocyte proliferation stimulated by activators of protein kinase C and proliferation stimulated by IL-2. Possible role for intracellular cAMP.

The regulation of the activation of T lymphocyte proliferation is not well understood. It is known that the tumor promoter, PMA, which activates protein kinase C (PKC), can induce the proliferation of several murine CTL clones; in combination with calcium ionophores, which raise the level of intracellular Ca2+, PMA can also stimulate the proliferation of several HTL clones. Activation of the TCR is believed to result in the liberation of diacylglycerol, which is an activator of PKC, and inositol 1,4,5-trisphosphate, which stimulates an increase in intracellular levels of calcium. We now report that pretreatment with cholera toxin (CT) inhibits the proliferation of murine T cell clones stimulated through the TCR/CD3 complex. In addition, CT-pretreatment blocks the proliferation of CTL clones activated with PMA or of HTL clones activated with PMA + calcium ionophore. In contrast, CT-pre-treatment inhibits much less effectively (100- to 1000-fold) the proliferation of these T cell clones stimulated with IL-2. Furthermore, activators of PKC, but not IL-2, potentiate the CT-induced cAMP elevation in T cell clones. The ability of CT to inhibit much more effectively the proliferation triggered by putative activators of PKC than that induced by IL-2 may be mediated by cAMP-dependent mechanisms.

Adenosine Monophosphate↗
PubMed1988

Bradykinin induces the bi-phasic production of lysophosphatidyl inositol and diacylglycerol in a dorsal root ganglion X neurotumor hybrid cell line, F-11.

Bradykinin acts on the dorsal root ganglion X neuroblastoma hybrid cell line F-11 to stimulate the rapid elevation of inositol trisphosphate (IP3) and intracellular calcium. We now show an equally rapid release of arachidonyl labeled diacylglycerol (DAG), (243 +/- 32% of control). This first peak of diacylglycerol production was inhibitable by either pretreatment with 200 ng/ml of pertussis toxin overnight or by 10 nM tetradecanoylphorbol acetate (TPA). In addition, a second, more sustained release occurred, plateauing at approximately five minutes (304 +/- 16%). The second peak of DAG was unaffected by these TPA or pertussis pre-incubations. Simultaneous analysis of inositol-labeled phospholipids showed that the initial IP3 and DAG peaks corresponded to initial decreases in phosphoinositides PIP2 and PIP whereas PI increased slightly over this same time period. In contrast, at 5-30 minutes, PIP2 and PIP returned to normal levels, but PI gradually decreased to 75% of control values. Likewise, TPA blocked this early PIP and PIP2 breakdown, but had no effect on the delayed breakdown of monophosphatidylinositol (PI). Bradykinin also induced an equally rapid increase in lysophosphatidyl inositol (lyso-PI) with a peak around 10-30 seconds, and a second more sustained peak after 10 minutes. This production of lyso-PI was not affected by prior treatment with TPA or pertussis toxin. The initial and the sustained phases of diacylglycerol production probably result from different biochemical mechanisms and/or substrates.

Animals↗
PubMed1988

Abnormal cathepsin B activity in Batten disease.

Fibroblasts cultured from patients with various forms of neuronal ceroid-lipofuscinosis (NCL; Batten disease) showed variably decreasing cathepsin B activity with increasing passage number and months in culture in the presence of fetal calf serum. Cathepsin H activity and that of a wide range of lysosomal hydrolases was unaffected by these conditions. Cathepsin B activity was assayed either colorimetrically (N alpha-benzoyl-DL-Arg-beta-naphthylamide; BANA), fluorimetrically (Z-Arg-Arg-methylcoumarin), or autoradiographically, following NaDodSO4-12.5% polyacrylamide gel electrophoresis ([125]Tyr-Ala-Lys-Arg-CH2Cl) and was found to be lysosomal in localization. Fractionation of disrupted fibroblasts on a Percoll gradient showed evidence of abnormally buoyant lysosomes in some NCL patients, and these tended to be low in cathepsin B but rich in other lysosomal hydrolases. Our data do not support a primary defect in cathepsin B as the basic defect in NCL. However, a possible explanation for various studies implicating a protease defect in NCL is that cathepsin B was highly sensitive to inactivation by peroxides and aldehydes. Thus hydrogen peroxide (0.3 mM) or 4-hydroxynonenal (1 nM) inactivated cathepsin B without inhibiting cathepsin H or lysosomal hydrolases such as alpha-L-fucosidase. Since peroxides and 4-hydroxynonenal have been shown to accumulate in NCL tissue (despite apparently normal peroxidase activity), we tested the possibility of a defect in the removal of peroxidized lipids from phospholipids as the primary defect in NCL. The nociceptive peptide bradykinin (BK) normally initiates a cascade involving receptor-mediated phospholipase C activation and release of arachidonate and prostanoids from cultured skin fibroblasts. Release of [3H]arachidonate by BK was deficient in NCL fibroblasts, suggesting that the primary defect in NCL could involve the deficiency of a specific phospholipase A2 activity.

Acid Phosphatase↗
PubMed1988

Extra embryonic/fetal karyotypic discordance during diagnostic chorionic villus sampling.

From a total of 1312 diagnostic chorionic villus samplings (CVS) there were 22 which showed discordance between the karyotype of the chorionic villi and that of the fetus. This frequency was some 20-fold higher than that reported at amniocentesis. In the majority of discordant cases, the fetal karyotype was normal while the placental karyotype was mosaic. In four cases, the placental karyotype was non-mosaic (a trisomy 16, a monosomy X, and two tetraploids) while the fetal karyotype was normal. In one case, the placenta was trisomy 18 while the fetus was mosaic. There were two 'false-negative' results where short-term methods showed only normal cells while both long-term cultures of chorionic villi and fetal cells were mosaic, in one 46,XY/47,XXY and in the other 46,XY/47,XY,+21.

Biopsy, Needle↗
PubMed1988

Reduced P3 amplitude of the event-related brain potential: its relationship to language ability in autism.

Several studies have found that P3 amplitude of the auditory event-related potential is smaller in autistic than in normal children. The present study investigated whether this characteristic bears any relationship to the degree of language impairment and/or level of intellectual ability of autistic persons. Seventeen autistic children, ranging from 8-19 years of age, and 17 age- and gender-matched normal children participated. Event-related potentials to phonetic ("Da") and chord (piano) stimuli were recorded from three scalp locations: vertex (Cz), right hemisphere (RH), and left hemisphere (LH), during a discrimination task. A battery of language tests was given to autistic children. Compared to normal subjects, autistic subjects showed a significantly smaller P3 amplitude to phonetic stimuli for Cz and LH recording sites. However, no group difference in P3 amplitude to the phonetic stimulus was found for the RH. Furthermore, no group differences in P3 amplitude were found for the chord stimulus at any recording site. Impaired language ability was related to greater RH P3 amplitude, particularly to the chord stimulus. The possibility of differential hemispheric involvement in the attentional deficits of autistic children is raised.

Adolescent↗
PubMed1988

Oligodendrocyte substratum adhesion modulates expression of adenylate cyclase-linked receptors.

The molecular mechanisms of myelin formation/reformation in the central nervous system are unknown. In previous work we have demonstrated that mature oligodendrocytes (OLG) respond to a signal(s), elicited by their adhesion to a substratum, by turning on a myelinogenic metabolism. Events occurring within 24 hr of adhesion include generation of diacylglycerol, activation of protein kinase C, phosphorylation of myelin basic protein, and enhanced synthesis of myelin lipids and proteins. To elucidate the mechanism(s) of signal transduction, we have investigated whether OLG-substratum interaction influences the level of basal cAMP and the expression of receptors coupled to adenylate cyclase. By using ovine brain OLG we have found that adhesion to a polylysine-coated surface for 24 hr increased the basal level of cAMP 2-fold and altered the expression (assessed by cAMP production) of receptors coupled to adenylate cyclase. Isoproterenol (beta-adrenergic agonist) augmented cAMP from 4 to 26 pmol/mg of protein in adhering OLG but had no such effect in nonattached OLG. Adhesion of OLG was accompanied by rapid synthesis of ethanolamine plasmalogen, a class of lipids believed to be associated with beta-adrenergic receptors. Nonattached OLG responded to prostaglandin E1 with only a 3-fold stimulation in their cAMP content; in attached OLG, 6-fold stimulation was observed. In contrast, vasoactive intestinal polypeptide elicited a 3-fold increase in cAMP in nonattached OLG but, following 24 hr of attachment, OLG did not respond to vasoactive intestinal polypeptide. The increase of cellular cAMP levels was accompanied by a 2.5-fold gain in protein kinase A. OLG-substratum adhesion resulted also in phosphorylation of the OLG/myelin protein, 2',3'-cyclic nucleotide 2'-phosphodiesterase, which proved to be a substrate for cAMP and phospholipid-, Ca2+-dependent protein kinases. These findings, in conjunction with our earlier work, implicate cAMP and diacylglycerol in signaling myelinogenesis; they suggest that phosphorylation/dephosphorylation of myelin basic protein and 2',3'-cyclic nucleotide 2'-phosphodiesterase may be key processes in the cascade of events that are initiated by adhesion of OLG to a polylysine surface (possibly acting as a surrogate for axons) and culminate in the reformation of myelin.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1988

Neuromodulator-mediated phosphorylation of specific proteins in a neurotumor hybrid cell line (NCB-20).

Mouse neuroblastoma X embryonic Chinese hamster brain explant hybrid cell line (NCB-20) forms functional synapses when intracellular cyclic AMP levels are elevated for a prolonged period of time. NCB-20 cells were labeled with [32P]orthophosphate under conditions where 2-chloroadenosine gave maximum increases of 32P incorporation into tyrosine hydroxylase in nerve growth factor dibutyryl cyclic AMP-differentiated PC12 (pheochromocytoma) cells. When NCB-20 cells were exposed to activators [5-hydroxytryptamine (5-HT), prostaglandin E1, or forskolin], resulting in activation of cyclic AMP-dependent protein kinase, increased 32P incorporation into two major proteins [130 kilodaltons (kDa) and 90 kDa] occurred. 5-HT (in the presence of phosphodiesterase inhibitor, isobutylmethylxanthine) gave a three- to fourfold increase, and forskolin a four- to sevenfold increase in 32P incorporation into the 90-kDa protein. [D-Ala2,D-Leu5]-enkephalin, which decreased cyclic AMP levels and reversed the 2-chloroadenosine-stimulated phosphorylation of tyrosine hydroxylase in differentiated PC12 cells, also reversed the stimulation of phosphorylation of the 90-kDa protein in NCB-20 cells. Pretreatment of NCB-20 cells with a calcium ionophore, A23187, gave increased phosphorylation of the 90- and 130-kDa proteins, but phorbol esters such as 12-O-tetradecanoylphorbol 13-acetate (tumor promoting agent), cell depolarization with high K+, or pretreatment with dibutyryl cyclic GMP had no effect on phosphorylation of these proteins. In contrast, phosphorylation of an 80-kDa protein was decreased by forskolin, but increased following activation of the calcium/phospholipid-dependent kinase with tumor promoting agent. Neither the 90-kDa nor the 80-kDa protein showed any immunological cross-reactivity with synapsin, a major synaptic protein known to be phosphorylated by cyclic AMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase, but not calcium/phospholipid-dependent protein kinase. This suggests that in NCB-20 cells, several unique proteins can be phosphorylated by cyclic AMP-dependent protein kinase in response to hormonal elevation of cyclic AMP levels. In contrast, an 80-kDa protein is the primary substrate for calcium/phospholipid-dependent protein kinase, and its phosphorylation is inhibited by agents that elevate cyclic AMP levels and thereby activate cyclic AMP-dependent protein kinase.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Molecular heterogeneity in lysosomal storage diseases. Alpha-fucosidase and N-acetyl-beta-D-hexosaminidase deficiency variants.

The availability of specific antibodies and cDNA probes for lysosomal hydrolases has revealed unexpected heterogeneity among the human inherited lysosomal storage diseases. Using alpha-fucosidase and N-acetyl-beta-D-hexosaminidase deficiency variants as examples, it has been determined that a lysosomal hydrolase deficiency can result from DNA deletion mutations, failure to synthesize mRNA because of defective splicing, posttranslational defects in assembly, and synthesis of a precursor enzyme that is prematurely proteolytically degraded through lack of a protective protein. In some cases (fucosidosis), the different genotypes cannot be distinguished phenotypically, whereas in others (beta-hexosaminidoses) the phenotypes can range from infantile neurodegeneration through juvenile motor neuron disease to adult neurodysfunction. Biochemical studies on both diseases have revealed several distinct genotypes. We show that some forms of fucosidosis result from unstable enzyme that can be stabilized by protease inhibitors, whereas partial beta-hexosaminidase deficiencies cannot be corrected by these protease inhibitors.

Cells, Cultured↗
PubMed1988

Genetically determined hypercholesterolemia in a rhesus monkey family due to a deficiency of the LDL receptor.

A family of rhesus monkeys comprising a sire, a dam, and four male offspring were fed a cholesterol-free Purina Chow diet for several months. The sire, 431-J, and two of the offspring, B-8204 and B-8806, had persistent plasma cholesterol levels in the range of 100-130 mg/dl, whereas the dam, 766-I, and the two other offspring, B-1000 and B-7643, exhibited a marked hypercholesterolemia in the 250-300 mg/dl range associated with an elevation of plasma LDL and apoB. When fed for 12 weeks a diet containing 12.5% lard and 0.25% cholesterol, sire, dam, B-1000 and B-7643 exhibited a marked hypercholesterolemia (500-800 mg/dl range), whereas B-8204 and B-8806 developed only a modest hypercholesterolemia (200-250 mg/dl). All animals were Lp[a]+. Skin fibroblasts from each animal and from control cells were grown in 10% fetal calf serum, transferred to 10% lipoprotein-deficient serum for 48 hr, and then incubated at 4 degrees C or 37 degrees C with 125I-labeled Lp[a]-free LDL. The fibroblasts from dam and offspring B-1000 and B-7643 bound and internalized 125I-labeled LDL less efficiently than control cells. Mathematical analyses of the 4 degrees C binding data indicated that there were no significant differences in LDL binding affinity between test and control cells suggesting that cells from the animals with a spontaneous hypercholesterolemia had a decreased number of LDL receptors. This conclusion was supported by the results of ligand and immunoblot analyses carried out on cell lysates separated by gradient gel electrophoresis. We conclude that a genetically determined LDL receptor deficiency was responsible, in part, for the spontaneous hypercholesterolemia observed in three out of the six family members and that this deficiency accounted for the hyperresponsiveness to a dietary fat and cholesterol challenge by the dam and the two offspring, B-1000 and B-7643. The hyperresponsiveness noted in the sire that had no evidence for LDL-receptor deficiency illustrates that factors other than the LDL receptor were responsible for the hypercholesterolemia attending the fat challenge.

Animals↗
PubMed1987

Apparent cathepsin B deficiency in neuronal ceroid lipofuscinosis can be explained by peroxide inhibition.

Fibroblasts from patients with various forms of neuronal ceroid lipofuscinosis (NCL or Batten's disease) showed decreasing cathepsin B activity with increasing passage number and time in culture. In contrast, other lysosomal hydrolase activities were largely unaffected. Cathepsin B activity, was found to be associated with the lysosome-enriched fraction following cell disruption and Percoll gradient fractionation. Exposure of fibroblasts to low concentrations (less than 0.1 mM) of hydrogen peroxide either in vivo or in vitro resulted in a dose-dependent loss of cathepsin B activity with no concomitant loss in cathepsin H activity or lysosomal hydrolase activity. These results suggest that a primary defect resulting in accumulation of abnormal peroxides could produce a secondary cathepsin B inhibition in lysosomes and lead to observed peptide and dolichol accumulation in NCL.

Cathepsin B↗
PubMed1987

Evidence for two catabolic endoglycosidase activities in beta-mannosidase-deficient goat fibroblasts.

Cultured skin fibroblasts derived from Nubian goats deficient in lysosomal beta-mannosidase, which had previously been shown to accumulate storage oligosaccharides with the structures Man beta 4GlcNAc beta 4GlcNAc and Man beta 4GlcNAc (in the ratio of 2.7:1) were evaluated for their ability to catabolize exogenous [3H]GlcN-labelled glycoproteins isolated from the secretions of cultured goat or human fibroblasts. Regardless of the source of exogenous labelled glycoprotein, affected goat fibroblasts took up the labelled glycoprotein from the culture medium and subsequently accumulated the same major labelled oligosaccharide, identified as Man beta 4GlcNAc beta 4GlcNAc; no such oligosaccharide accumulated in normal goat fibroblasts under the same conditions. Tunicamycin-treated affected fibroblasts also took up labelled exogenous glycoprotein and accumulated labelled storage trisaccharide, further suggesting the direct accumulation of storage trisaccharide from impaired glycoprotein-associated oligosaccharide catabolism. Treatment of metabolically labelled affected fibroblasts with leupeptin, an inhibitor of lysosomal cathepsins, resulted in the 2- to 6-fold inhibition of trisaccharide accumulation, while having little effect on the uptake of [3H]GlcN or the accumulation of labelled disaccharide. The results are most consistent with the presence of two endoglycosidases, an endo-beta-N-acetylglucosaminidase and an endo-aspartylglucosaminidase, in goat fibroblasts. These two activities, rather than heterogeneous core oligosaccharide structures, are responsible for the ultimate accumulation of storage oligosaccharides with one and two GlcNAc residues at their reducing terminus.

Animals↗
PubMed1987

Perspective-taking ability and its relationship to the social behavior of autistic children.

A study was undertaken to assess the relationship between perspective-taking ability and the quality of social behavior in autistic children. Sixteen autistic children ranging from 6 to 14 years of age were administered three types of perspective-taking tasks (perceptual, conceptual, and affective), as well as the Peabody Picture Vocabulary Test and the Leiter International Performance Scale. Two measures of social behavior were taken: the Vineland Social Maturity Scale and the Social Behavior Rating Scale, designed for the present study. It was found that perspective-taking ability was significantly correlated with both measures of social skills, whereas receptive vocabulary and nonverbal intelligence were not. These results suggest that the social impairments of autistic children may be related to specific deficits in social cognition.

Adolescent↗
PubMed1987

Function of the adrenal cortex in patients with major depression.

Failure to suppress cortisol secretion after administration of dexamethasone occurs in up to 50% of depressed patients. To test whether this hypothalamic-pituitary-adrenal (HPA) overactivity is associated with adrenocortical hyperresponsiveness, we performed dexamethasone suppression tests (DSTs) and adrenocorticotropic hormone (ACTH) stimulation tests in depressed subjects and subjects with other psychiatric disorders. Three groups were defined: depressed nonsuppressors, depressed suppressors, and other suppressors. While predexamethasone and postdexamethasone cortisol concentrations were greater in the depressed nonsuppressor group, ACTH concentrations did not differ among groups. After receiving alpha-ACTH[1-24] (4.2 micrograms/kg), depressed nonsuppressors had greater increases in stimulated cortisol secretion than the other groups. These results demonstrate that in a subgroup of depressed patients, HPA overactivity is associated with adrenocortical hyperresponsiveness.

Adrenal Cortex↗
PubMed1987

Tripronuclear human oocytes: altered cleavage patterns and subsequent karyotypic analysis of embryos.

Between 1 and 4% of human oocytes fertilized in vitro are tripronuclear. It has been reported that these tripronuclear oocytes can develop to grossly normal-appearing morulae and that chromosomally, these embryos could be triploid, diploid, or severely depleted. The etiology and proportion of apparently diploid and aneuploid embryos deriving from tripronuclear human oocytes is unknown. This study provides evidence for the first time that most (18 of 29) tripronuclear human oocytes cleave directly to 3-cells at the first cleavage division. These embryos have a severely abnormal (but not triploid) chromosomal complement. Furthermore, some (4 of 29) tripronuclear human oocytes cleave to 2-cells plus an extrusion, and these embryos are diploids, whereas some (7 of 29) cleave to 2-cells, and these embryos are triploid after the first cleavage division. These findings demonstrate that most tripronuclear human oocytes have an altered cleavage pattern at the first cleavage division, that most tripronuclear human oocytes (76% in this study) do not develop into triploid embryos, and that a correlation exists between the pattern of the first cleavage division and the subsequent karyotype of these embryos. Insight into the mechanisms by which these oocytes fail to develop into triploid embryos is also provided.

Aneuploidy↗
PubMed1987

Investigation of HTLV-3 serology in a renal transplant population.

From June 1977 to March 1985, 572 renal transplants were performed at The University of Texas Medical School at Houston. This represented 220 patients (151 cadaveric [CAD] and 69 living-related donor [LRD] recipients) treated with azathioprine and prednisone (Aza-Pred) and 352 patients (250 CAD and 102 LRD) treated with cyclosporine (CsA) and Pred. Sera from each recipient before and after transplant (Tx) as well as from each of their 436 donors (265 CAD and 171 LRD) were retrospectively tested for the presence of antibody to the human T cell lymphotrophic virus type III (HTLV-3) by enzyme immunoassay (EIA) and Western Blot analysis. Of the 436 donors tested, only 1/265 (0.38%) CAD donors were both EIA repeatedly reactive and Western Blot positive, whereas none of the 171 LRD were reactive. Pre-Tx, 4/401 (1.0%) CAD and 1/171 (0.6%) LRD recipient sera were EIA repeatedly reactive, however, all 5 were to be Western Blot negative. Post-Tx, 4.2% of the sera (24/572, 4 LRD and 20 CAD recipients) were EIA-reactive. All 20 CAD recipient sera were subsequently found to be negative with Western Blot testing. However, 2 LRD sera (2/572, 0.35%) displayed EIA reactivity as well as Western Blot positivity. One LRD, Western-Blot-positive recipient is alive and well with a functioning allograft 39 months post-Tx, whereas the second LRD, Western Blot positive recipient died of septic complications 16 months post-Tx. Finally, the recipient of the Western-Blot-positive CAD allograft is alive with a well-functioning graft and remains EIA and Western-Blot-negative 36 months post-Tx.

Antibodies, Viral↗