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Biomedical subjects

K Pham

Publications and source records attributed to K Pham.

At least 19 recordsLinked to original sources
PubMed2005

Fear learning transiently impairs hippocampal cell proliferation.

We sought to determine whether contextual fear conditioning, a hippocampal-dependent task, would affect neurogenesis in the dentate gyrus of the hippocampus, and if so, to identify which aspect of the training experience accounts for the change. The immediate shock deficit paradigm was used, together with bromodeoxyuridine immunohistochemistry, to isolate the contribution of different aspects of contextual fear conditioning to neurogenesis. Contextual fear learning caused a 33% decrease in the number of proliferating cells that was anatomically restricted to the dentate gyrus with no change in cell survival or differentiation. This attenuation was not related to exposure to the conditioned stimulus alone, the footshock unconditioned stimulus alone, or the expression of fear to the context after training. Instead, the effect of context conditioning on cell proliferation appears to be specifically due to the formation of an association between the context and shock during training, an amygdala dependent function.

Animals↗
PubMed2005

Limited-dose Daclizumab versus Basiliximab: a comparison of cost and efficacy in preventing acute rejection.

The purpose of this study was to compare the efficacy and cost of the limited-dose Daclizumab regimen to that of the standard-dose Basiliximab regimen. Two antibody induction regimens were compared in patients aged 18 years and older who received renal transplants from January 2002 to September 2003 and completed interleukin (IL)-2R antibody induction with standard-dose Basiliximab (20 mg x 2 doses) or limited-dose Daclizumab (1 mg/kg x 2 doses). The primary outcome measure was the incidence of acute rejection. Secondary outcomes included cost, changes in serum creatinine level, and delayed graft function. Of the 46 patients randomized, 42 patients completed the 6-month follow-up. Mean serum creatinine level at time of discharge was originally higher in the limited-dose Daclizumab group than the standard-dose Basiliximab group (1.89 vs 1.57, respectively). By 1, 3, and 6 months, mean serum creatinine values were similar between both groups, with a trend toward lower mean serum creatinine values in the limited-dose Daclizumab group. The incidence of acute rejection was also similar between the groups (6% vs 7%). The average cost difference between the 2 regimens was approximately $715. This study suggests that a limited-dose Daclizumab regimen may be an efficacious and less costly alternative to the standard-dose Basiliximab regimen for antibody induction therapy following renal transplantation.

Adult↗
PubMed2005

Factors influencing the diagnosis and treatment of periodontal disease by dental practitioners in Victoria.

BACKGROUND: Healthy periodontal tissues are essential to overall dental health. Therefore, the detection and management of periodontal disease is an integral part of general dental practice. The aim of this study was to investigate confidence in diagnosis and management of periodontal disease by general dental practitioners (GDPs), assess if the Dental Practice Board guidelines on periodontal record keeping are being addressed, and, if necessary, try to find ways of improving the periodontal knowledge of GDPs. METHODS: A survey assessing practitioner confidence in diagnosing and treating periodontal disease was sent to a random selection of 550 dental care providers registered with the Dental Practice Board of Victoria. RESULTS: Two hundred and eighty five (51.8 per cent) of questionnaires were returned completed. It was found that 79.7 per cent of the sampled population screened all new patients for periodontal disease. The majority of respondents felt confident to diagnose and treat gingivitis and initial periodontitis. However, only 61.9 per cent felt confident to diagnose aggressive/early onset periodontitis, and many were not confident in treating advanced periodontitis (36.3 per cent) or aggressive periodontitis (51.6 per cent). The majority of dentists reported that they provided most of the non surgical periodontal therapy to their patients, while most surgical treatments were referred to specialist periodontists. Factors deemed to be important in influencing the decision to provide periodontal treatment included level of training and ability to motivate patients to improve oral hygiene. Many responents requested periodontic continuing education (CE) courses be run. CONCLUSIONS: Most of the dentists surveyed were confident to diagnose periodontal disease and to treat the more common presentations of periodontal disease. There is some evidence to suggest that some practitioners are not following the minimum requirements set by the Dental Practice Board of Victoria in relation to periodontal record keeping. The results also indicate a need for more periodontic CE courses in Victoria.

Clinical Competence↗
PubMed2004

Chronic restraint stress and chronic corticosterone treatment modulate differentially the expression of molecules related to structural plasticity in the adult rat piriform cortex.

Stress and stress-related hormones induce structural changes in neurons of the adult CNS. Neurons in the hippocampus, the amygdala and the prefrontal cortex undergo neurite remodeling after chronic stress. In the hippocampus some of these effects can be mimicked with chronic administration of adrenal steroids. These changes in neuronal structure may be mediated by certain molecules related to plastic events such as the polysialylated form of the neural cell adhesion molecule (PSA-NCAM). The expression of PSA-NCAM persists in the adult hippocampus and it is up-regulated after chronic stress. The piriform cortex also displays considerable levels of PSA-NCAM during adulthood and indirect evidence suggests that it may also be the target of stress and stress related-hormones. Using immunohistochemistry we have studied the expression of PSA-NCAM and doublecortin (DCX; another protein implicated in neuronal structural plasticity) in the piriform cortex of adult rats subjected either to 21 days of chronic restraint stress or to oral corticosterone administration during the same period. Our results indicate that chronic stress and chronic corticosterone administration have differential effects on the expression of PSA-NCAM and DCX. While chronic stress increases the number of PSA-NCAM- and DCX-immunoreactive cells in the piriform cortex layer II, chronic corticosterone administration decreases these numbers. These findings indicate that stress and adrenal steroids affect the piriform cortex and suggest that in this region, as in the hippocampus, they may induce structural changes. This is a potential mechanism by which stress and corticosterone modulate functions of this limbic region, such as its participation in olfactory memory.

Animals↗
PubMed2003

Wnt ligand expression in malignant melanoma: pilot study indicating correlation with histopathological features.

AIMS: Secreted Wnt ligands are key proteins regulating cell-cell interactions and cell growth and differentiation. These proteins, along with other components of the Wnt signalling pathway, are involved in the malignant transformation of various human cancers, including malignant melanoma. This study defines the expression of several members of the Wnt ligand family and correlates their expression with histological characteristics. METHODS: The expression of Wnt2, Wnt5a, Wnt5b, Wnt7b, and Wnt10b was defined by in situ, antisense RNA hybridisation of paraffin wax embedded sections of benign naevi and malignant melanoma. Immunoperoxidase based antibody staining was used to define the expression of frizzled (Fz) receptors. RESULTS: All naevi tested strongly expressed Wnt2, Wnt5a, Wnt7b, and Wnt10b. Melanomas characterised by small, uniform cells expressed each of the Wnts in a pattern similar to that seen for benign naevi. In contrast, melanomas characterised by large, pleomorphic cells expressed Wnt10b but did not express Wnt2 and had low levels of expression of Wnt5a. Expression of Wnt7b was variable in these melanomas. Fz receptor expression was present at a low level in normal epithelium and all naevi and melanomas. CONCLUSIONS: The expression pattern of Wnt ligands in malignant melanoma correlates with histopathological features and may provide a basis for the molecular classification of this disease.

Biomarkers, Tumor↗
PubMed2002

Aggregation of human platelets by gingipain-R from Porphyromonas gingivalis cells and membrane vesicles.

The hypothesis that there is an association between periodontitis and cardiovascular disease suggests new lines of research on the mechanism whereby oral bacteria might exert systemic effects. This study was conducted to ascertain and quantitate the effect of Porphyromonas gingivalis on human platelets in vitro. A second related objective was to purify and identify the aggregating vector. Aggregation was measured by platelet turbidometry and gingipain-R was purified from P. gingivalis membrane vesicles by Sepharose 2B and hydroxyapatite chromatography. The in vitro aggregation of platelets requires that at least 1.0 x 10(4) cells be stirred with 1.35 x 10(8) platelets. The specific activity is substantially increased in the membrane vesicles that are shed by this bacterium. Aggregability was due to gingipain-R activity, a potent cysteine protease that was found to be highly concentrated in the membrane vesicle fraction. The enzyme was purified 18-fold in high yield from the membrane vesicles, and consists of two noncovalently linked proteins that migrate at 49 and 44 kDa on SDS-PAGE. Aggregation of platelets by gingipain-R was shown to be dose-dependent, and inhibited by leupeptin and arginine, but not by anti-thrombin III. This is the first report enumerating the specific number of cells and lowest concentration of membrane vesicles necessary to evoke a full human platelet response, and the first report to assign this activity to gingipain-R.

Adhesins, Bacterial↗
PubMed2001

Genome-wide gene expression profiles of the developing mouse hippocampus.

We have analyzed the developmental molecular programs of the mouse hippocampus, a cortical structure critical for learning and memory, by means of large-scale DNA microarray techniques. Of 11,000 genes and expressed sequence tags examined, 1,926 showed dynamic changes during hippocampal development from embryonic day 16 to postnatal day 30. Gene-cluster analysis was used to group these genes into 16 distinct clusters with striking patterns that appear to correlate with major developmental hallmarks and cellular events. These include genes involved in neuronal proliferation, differentiation, and synapse formation. A complete list of the transcriptional changes has been compiled into a comprehensive gene profile database (http://BrainGenomics.Princeton.edu), which should prove valuable in advancing our understanding of the molecular and genetic programs underlying both the development and the functions of the mammalian brain.

Animals↗
PubMed2000

Effect of an essential oil-containing antiseptic mouthrinse on induction of platelet aggregation by oral bacteria in vitro.

BACKGROUND: With an increasing body of data suggesting an association between periodontitis and cardiovascular disease, studies have been conducted to elucidate potential mechanisms by which oral bacteria might exert systemic effects. 2 oral bacteria, Streptococcus sanguis and Porphyromonas gingivalis, have been shown to induce platelet aggregation in vitro. This study was conducted to determine the effect of treatment with an essential oil mouthrinse (Listerine Antiseptic) on the platelet-aggregating activity of these organisms. METHOD: Bacteria were grown under standard culture conditions. S. sanguis ATCC strain 10556 was exposed for 3 min to the essential oil mouthrinse at either full strength or a 1:1 dilution, while P. gingivalis FDC strain 381 was exposed to the essential oil mouthrinse at a 1:10 dilution. Positive control cells were treated with Hanks balanced salt solution (HBSS). Aggregation was measured using a recording platelet aggregometer. The assay of each organism in its respective mouthrinse dilution(s) or HBSS was repeated 5 times. RESULTS: In all cases, the HBSS-treated organisms induced platelet aggregation, with mean(+/-S.E.) lag times of 12.30 (+/-1.36) min and 11.36 (+/-0.58) min for P. gingivalis and S. sanguis, respectively. In contrast, treatment with the essential oil mouthrinse completely inhibited the platelet aggregating activity of P. gingivalis and of S. sanguis exposed to the 1:1 mouthrinse dilution in all assays; the aggregating activity of S. sanguis treated with full-strength mouthrinse was completely inhibited in 4 of 5 assays, and inhibited by 75% in the 5th, for a mean inhibition of 95 +/- 1.5%. CONCLUSION: This study provides additional evidence that the essential oil mouthrinse can interfere with bacterial cell surface-associated activities which may have clinical relevance.

Drug Combinations↗
PubMed1999

On-line monitoring of radiotherapy beams: experimental results with proton beams.

Proton radiotherapy is a powerful tool in the local control of cancer. The advantages of proton radiotherapy over gamma-ray therapy arise from the phenomenon known as the Bragg peak. This phenomenon enables large doses to be delivered to well-defined volumes while sparing surrounding healthy tissue. To fully realize the potential of this technique the location of the high-dose volume must be controlled very accurately. An imaging system was designed and tested to monitor the positron-emitting activity created by the beam as a means of verifying the beam's range, monitoring dose, and determining tissue composition. The prototype imaging system consists of 12 pairs of cylindrical BGO detectors shielded in lead. Each crystal was 1.9 cm in diameter, 5.0 cm long, and separated by 0.5 cm from other detectors in the row. These are arranged in two rows, 60 cm apart, with the proton beam and tissue phantoms half-way between and parallel to the detector rows. Experiments were conducted with 150 MeV continuous and macro-pulsed proton beams which had beam currents ranging from 0.14 nA to 1.75 nA. The production and decay of short-lived isotopes, 15O and 14O, was studied using 1 min irradiations with a continuous beam. These isotopes provide a significant signal on short time scales, making on-line imaging possible. Macro-pulsed beams, having a period of 10 s, were used to study on-line imaging and the production and decay of long-lived isotopes, 13N, 11C, and 18F. Decay data were acquired and on-line images were obtained between beam pulses and indicate that range verification is possible, for a 150 MeV beam, after one beam pulse, to within the 1.2 cm resolution limit of the imaging system. The dose delivered to the patient may also be monitored by observing the increase in the number of coincidence events detected between successive beam pulses. Over 80% of the initial positron-emitting activity is from 15O while the remainder is primarily 11C, 13N, 14O with traces of 18F, and 10C. Radioisotopic imaging may also be performed along the beam path by fitting decay data collected after the treatment is complete. Using this technique, it is shown that variations in elemental composition in inhomogenous treatment volumes may be identified and used to locate anatomic landmarks. Radioisotopic imaging also reveals that 14O is created well beyond the Bragg peak, apparently by secondary neutrons.

Biophysical Phenomena↗
PubMed1997

RAP-1 is an Arabidopsis MYC-like R protein homologue, that binds to G-box sequence motifs.

An Arabidopsis cDNA clone encoding a DNA-binding protein, RAP-1, was isolated by southwestern screening of an Escherichia coli cDNA expression library. The protein contains a bHLH DNA-binding domain and is homologous to R proteins, regulating anthocyanin biosynthesis. RAP-1 binds to the sequence CACNTG. It is encoded by a single gene, which is expressed to high levels in root and stem and to low levels in leaf and flower. No expression could be detected in siliques. Rap-1 does not correspond to one of the known loci involved in anthocyanin biosynthesis, since it is located at a different map position. In contrast to the maize R protein Lc, RAP-1 did not induce anthocyanin biosynthesis in pea cotyledons. Thus, RAP-1 is a novel member of the bHLH class of DNA-binding proteins.

Amino Acid Sequence↗
PubMed1997

Oral feeding of renal tubular antigen abrogates interstitial nephritis and renal failure in Brown Norway rats.

We have examined whether oral feeding of antigen can regulate the expression of autoimmune interstitial nephritis induced by antigen-in-adjuvant (RTA/CFA) immunization of Brown Norway rats. Male rats were divided into six experimental groups: Group I, RTA/CFA immunization alone; Groups II, III, and IV were pretreated with 1 mg (Group II), 5 mg (Group III), and 25 mg (Group IV) of oral tubular antigen every other day for ten days, followed by RTA/CFA immunization; Group V was pretreated with a control antigen, followed by RTA/CFA immunization; and Group VI was immunized with CFA alone. Renal histology, inulin clearance, DTH responses to RTA, and IgG antibody responses to RTA were monitored as endpoints of the study. Our results demonstrated that Group III and IV animals had significantly less severe renal injury, as assessed by inulin clearance and extent of renal cortical involvement by mononuclear cells. Group II and IV animals had suppressed DTH responses, and only Group IV animals had significantly depressed antigen-specific IgG serum titers. Group III animals had neither suppressed DTH responses or IgG titers. We conclude that oral administration of tubular antigen can modulate the intensity of interstitial nephritis produced by immunization, but that the regulatory mechanism is not dependent (at all doses of fed antigen) on suppressed DTH reactivity to RTA or suppressed antigen-specific IgG.

Administration, Oral↗
PubMed1996

Characterization of a zinc-dependent transcriptional activator from Arabidopsis.

The C2-H2 zinc-finger is a widely occurring DNA binding motif, usually present as tandem repeats. The majority of C2-H2 zinc-finger proteins that have been studied are derived from animals. Here, we characterize a member of a distinct class of plant C2-H2 zinc-finger proteins in detail. A cDNA clone encoding a DNA binding protein from Arabidopsis was isolated by SouthWestern screening. The protein, termed ZAP1 (Zinc-dependent Activator Protein-1), is encoded by a single copy gene, which is expressed to similar levels in root and flower, to a somewhat lower level in stem and to low levels in leaf and siliques. The optimal binding site was determined by random binding site selection, and the consensus sequence found is CGTTGACCGAG. The homology between ZAP1 and other DNA binding proteins is restricted to a repeated region of a stretch of 24 highly conserved amino acids followed by a zinc-finger motif (C-X4-C-X22-23-H-X1-H). The C-terminal zinc-finger region is essential for DNA binding, whereas deletion of the N-terminal one resulted in 2.5-fold reduced binding affinity. Binding of ZAP1 to DNA was abolished by metal-chelating agents. The activation domain as determined in yeast is adjacent to and possibly overlapping with the DNA binding domain. Particle bombardment experiments with plant cells showed that ZAP1 increases expression of a gusA reporter gene that is under control of ZAP1 binding sites. We conclude that ZAP1 is a plant transcriptional activator with a C2-H2 zinc-finger DNA binding domain.

Amino Acid Sequence↗
PubMed1996

Binding specificity and tissue-specific expression pattern of the Arabidopsis bZIP transcription factor TGA2.

The binding specificity and tissue-specific expression pattern of TGA2 (AHBP-1b), an Arabidopsis bZIP transcription factor have been determined. Filter-binding and gel-shift assays showed that TGA2 has high affinity for C-boxes (ATGACGTCAT). In this respect TGA2 is similar to other members of the Arabidopsis TGA family (such as TGA1, TGA3 and OBF4) and to tobacco TGA1a. Genomic Southern blot analysis confirmed that TGA2 is a member of the gene family. Northern blot analysis showed that the gene is expressed at similar levels in root, stem, leaf and flower t at somewhat lower levels in siliques. TGA3 was also found to be expressed at the same level throughout the plant, whereas genes encoding TGA1 and OBF4 have relatively high RNA expression levels in root. The differential expression of these genes suggests that they have distinct functions.

Arabidopsis↗
PubMed1996

Dentin ablation with three infrared lasers.

BACKGROUND AND OBJECTIVE: Lasers are used for caries removal in enamel and dentin, but are currently limited in their ability to remove sound tooth structure. In this study plasma interaction regimes are investigated as the principal factor determining the ablation characteristics. STUDY DESIGN/MATERIALS AND METHODS: Three ablation parameters are considered: ablation rates (AR), surface temperatures (ST), and surface morphological characteristics. The three lasers investigated were Er:YSGG with wavelength (WL) of 2.94 mu m and pulse duration (PD) of 250 mu s, Ho:YSGG at 2.1 mu m and 250 mu s and an Nd:YAG with WL of 1.06 mu M and PD of 15ns. RESULTS: The highest surface temperatures were observed during Er:YSGG treatment (> 300 degrees C), moderate temperatures with the Ho:YSGG (150 degrees C), and lowest with the Nd:YAG (with highest surface temperature generally lower than 80 degrees C). Ablation rates were also compared and were shown to be highest with the Er:YSGG and Ho:YSGG, and lower with the Nd:YAG (< 3 mu m). In all systems, efficient ablation was observed only in the presence of plasma. In spite of their different wavelengths, for similar spot sizes, energy, and pulse duration, ablation rates of Ho:YSGG and Er:YSGG were found to be comparable. These were an order of magnitude larger than the ablation rates observed with the nanosecond system. CONCLUSION: Possible explanation for these observations is given in terms of plasma characteristics.

Dentin↗
PubMed1996

The 22 bp W1 element in the pea lectin promoter is necessary and, as a multimer, sufficient for high gene expression in tobacco seeds.

The pea lectin (Psl) gene encodes an abundant seed protein. Its seed-specific expression pattern is conserved in transgenic tobacco plants. Progressive 5' promoter deletions resulted in a gradual decrease of transcriptional activity in tobacco seed. A fragment of 115 bp still conferred seed-specific expression albeit at a low level. This fragment contains a 22 bp element (W1), which has been demonstrated to be important for seed-specific expression when coupled as a trimer to a heterologous TATA box (de Pater et al., Plant Cell 5:877-886, 1993). Here we show that deletion of W1 in the natural promoter context resulted in a strongly decreased level of gene expression. A 4 bp mutation of W1 reduced the expression of truncated derivatives of the Psl promoter. A single copy of W1 coupled to the TATA box of the CaMV 35S promoter directed low gene expression in seeds and leaves. Multimerization enhanced the expression in seeds up to 100-fold, to levels found with the Psl promoter, whereas the expression level in leaves remained low. These results demonstrate that the W1 element is an essential control element in the Psl promoter. When taken out of its natural context and multimerized, it is sufficient for high expression in seeds.

Base Sequence↗