Biomedical subjects

David J Anderson

Publications and source records attributed to David J Anderson.

68 records · Page 4Linked to original sources

PubMed2002

Divergent functions of the proneural genes Mash1 and Ngn2 in the specification of neuronal subtype identity.

The neural bHLH genes Mash1 and Ngn2 are expressed in complementary populations of neural progenitors in the central and peripheral nervous systems. Here, we have systematically compared the activities of the two genes during neural development by generating replacement mutations in mice in which the coding sequences of Mash1 and Ngn2 were swapped. Using this approach, we demonstrate that Mash1 has the capacity to respecify the identity of neuronal populations normally derived from Ngn2-expressing progenitors in the dorsal telencephalon and ventral spinal cord. In contrast, misexpression of Ngn2 in Mash1-expressing progenitors does not result in any overt change in neuronal phenotype. Taken together, these results demonstrate that Mash1 and Ngn2 have divergent functions in specification of neuronal subtype identity, with Mash1 having the characteristics of an instructive determinant whereas Ngn2 functions as a permissive factor that must act in combination with other factors to specify neuronal phenotypes. Moreover, the ectopic expression of Ngn2 can rescue the neurogenesis defects of Mash1 null mutants in the ventral telencephalon and sympathetic ganglia but not in the ventral spinal cord and the locus coeruleus, indicating that Mash1 contribution to the specification of neuronal fates varies greatly in different lineages, presumably depending on the presence of other determinants of neuronal identity.

Animals↗

PubMed2002

Differential regulation of nicotinic receptor-mediated neurotransmitter release following chronic (-)-nicotine administration.

The objective of this study was to compare nAChR-mediated neurotransmitter release from slices of rat striatum, frontal cortex and hippocampus following chronic (-)-nicotine (Nic) administration (tartrate salt, 2 mg/kg twice daily for 10 days). Binding studies were also conducted to measure changes in receptor density. Relative to saline-treated animals, the number of nAChRs measured by [(3)H]-cytisine (CYT) binding was significantly increased in all brain regions examined by 15% to 25% following chronic Nic administration. Using a relatively high throughput method to measure neurotransmitter release, we found that Nic, CYT, and (+/-)-epibatidine (EB) evoked similar concentration-dependent striatal [(3)H]-dopamine (DA) and hippocampal [(3)H]-norepinephrine (NE) release from both saline (rank order of potency for [(3)H]-DA: EB>CYT>Nic; pEC(50) values, EB (9 +/- 0.1), CYT (8 +/- 0.13), Nic (7.3 +/- 0.19); rank order potency for [(3)H]-NE: EB>Nic=CYT; pEC(50) values, EB (8 +/- 0.18), Nic (5.5 +/- 0.09), CYT (5.12 +/- 0.1)) -and Nic-treated animals (pEC(50) values [(3)H]-DA, EB (9.5 +/- 0.15), Nic (8 +/- 0.16, CYT (6.6 +/- 0.52); [(3)H]-NE, EB (8.4 +/- 0.23), Nic (5.19 +/- 0.1), CYT (5.18 +/- 0.29)). Although no change in potency was detected between the two treatment groups, the agonist efficacies in both tissues were significantly reduced by approximately 17-54% following chronic Nic administration. In contrast to striatum, treatment with Nic did not affect the maximal [(3)H]-DA response (efficacy) in the frontal cortex. However, as observed in the striatum, no change in agonist potency was observed in the frontal cortex following chronic Nic administration (pEC(50) values, saline; EB (9.2 +/- 0.2), >CYT (6.95 +/- 0.75) = Nic (6.9 +/- 0.16); Nic-treated, EB (9 +/- 0.42)>CYT (6.88 +/- 0.27) = Nic (7.1 +/- 0.17)). Chronic Nic treatment did not significantly affect KCl-evoked [(3)H]-NE release from hippocampus or [(3)H]-DA release from frontal cortex or striatum. Since previous work has demonstrated that different nAChR subtypes display various sensitivities to chronic Nic exposure, we suggest that the subtypes of nAChRs involved in regulating [(3)H]-DA release may be different in the striatum and frontal cortex. These results support findings from earlier studies comparing the pharmacology of nAChR-evoked striatal versus cortical [(3)H]-DA release.

Alkaloids↗

PubMed2002

A practical guide to the implementation of an effective incident reporting scheme to reduce medication error on the hospital ward.

This paper discusses an anonymous incident reporting scheme to reduce drug administration error on the hospital ward, as part of an effective, non-punitive, systems-focused approach to safety. Drug error is costly in terms of increased hospital stay, resources consumed, patient harm, lives lost and careers ruined. Safety initiatives that focus, not on blaming individuals, but on improving the wider system in which personnel work have been adopted in a number of branches of health care. However, in nursing, blame remains the predominant approach for dealing with error, and the ward has seen little application of the systems approach to safety. Safety interventions founded on an effective incident scheme typically pay for themselves in terms of dollar savings arising from averted harm. Recent calls for greater health-care safety require finding new ways to make drug administration safer throughout the hospital, and the scope for such safety gains on the hospital ward remains considerable.

Health Plan Implementation↗

PubMed2002

In vitro electrical properties for iridium oxide versus titanium nitride stimulating electrodes.

Stimulating electrode materials must be capable of supplying high-density electrical charge to effectively activate neural tissue. Platinum is the most commonly used material for neural stimulation. Two other materials have been considered: iridium oxide and titanium nitride. This study directly compared the electrical characteristics of iridium oxide and titanium nitride by fabricating silicon substrate probes that differed only in the material used to form the electrode. Electrochemical measurements indicated that iridium oxide had lower impedance and a higher charge storage capacity than titanium nitride, suggesting better performance as a stimulating electrode. Direct measurement of the electrode potential in response to a biphasic current pulse confirmed that iridium oxide uses less voltage to transfer the same amount of charge, therefore using less power. The charge injection limit for titanium nitride was 0.87 mC/cm2, contradicting other reports estimating that titanium nitride was capable of injecting 22 mC/cm2. Iridium oxide charge storage was 4 mC/cm2, which is comparable to other published values for iridium oxide. Electrode efficiency will lead to an overall more efficient and effective device.

Coated Materials, Biocompatible↗

PubMed2002

Arteriolar and venular patterning in retinas of mice selectively expressing VEGF isoforms.

The murine VEGF gene is alternatively transcribed to yield the VEGF(120), VEGF(164), and VEGF(188) isoforms, which differ in their potential to bind to heparan sulfate and neuropilin-1 and to stimulate endothelial growth. Here, their role in retinal vascular development was studied in mice selectively expressing single isoforms. VEGF(164/164) mice were normal, healthy, and had normal retinal angiogenesis. In contrast, VEGF(120/120) mice exhibited severe defects in vascular outgrowth and patterning, whereas VEGF(188/188) mice displayed normal venular outgrowth but impaired arterial development. It is noteworthy that neuropilin-1, a receptor for VEGF(164), was predominantly expressed in retinal arterioles. These findings reveal distinct roles of the various VEGF isoforms in vascular patterning and arterial development in the retina.

Animals↗

PubMed2002

Cardiovascular ephrinB2 function is essential for embryonic angiogenesis.

EphrinB2, a transmembrane ligand of EphB receptor tyrosine kinases, is specifically expressed in arteries. In ephrinB2 mutant embryos, there is a complete arrest of angiogenesis. However, ephrinB2 expression is not restricted to vascular endothelial cells, and it has been proposed that its essential function may be exerted in adjacent mesenchymal cells. We have generated mice in which ephrinB2 is specifically deleted in the endothelium and endocardium of the developing vasculature and heart. We find that such a vascular-specific deletion of ephrinB2 results in angiogenic remodeling defects identical to those seen in the conventional ephrinB2 mutants. These data indicate that ephrinB2 is required specifically in endothelial and endocardial cells for angiogenesis, and that ephrinB2 expression in perivascular mesenchyme is not sufficient to compensate for the loss of ephrinB2 in these vascular cells.

Animals↗

PubMed2002

Comparison of the generic neuronal differentiation and neuron subtype specification functions of mammalian achaete-scute and atonal homologs in cultured neural progenitor cells.

In the vertebrate peripheral nervous system, the proneural genes neurogenin 1 and neurogenin 2 (Ngn1 and Ngn2), and Mash1 are required for sensory and autonomic neurogenesis, respectively. In cultures of neural tube-derived, primitive PNS progenitors NGNs promote expression of sensory markers and MASH1 that of autonomic markers. These effects do not simply reflect enhanced neuronal differentiation, suggesting that both bHLH factors also specify neuronal identity like their Drosophila counterparts. At high concentrations of BMP2 or in neural crest stem cells (NCSCs), however, NGNs like MASH1 promote only autonomic marker expression. These data suggest that that the identity specification function of NGNs is more sensitive to context than is that of MASH1. In NCSCs, MASH1 is more sensitive to Notch-mediated inhibition of neurogenesis and cell cycle arrest, than are the NGNs. Thus, the two proneural genes differ in other functional properties besides the neuron subtype identities they can promote. These properties may explain cellular differences between MASH1- and NGN-dependent lineages in the timing of neuronal differentiation and cell cycle exit.

Animals↗

PubMed2001

Temporally compartmentalized expression of ephrin-B2 during renal glomerular development.

Glomerular development proceeds through the spatially ordered and sequential recruitment, proliferation, assembly, and differentiation of endothelial, mesangial, and epithelial progenitors. The molecular determinants of cell-cell recognition and targeting in this process have yet to be defined. The Eph/ephrin family of membrane receptors and counter-receptors are critical participants of developmental vascular assembly in extrarenal sites. Renal expression patterns of ephrin-B2 and EphB4 were investigated using mice expressing beta-galactosidase under control of ephrin-B2 or EphB4 promoters. The earliest glomerular expression of ephrin-B2 was identified in a subset of differentiating comma-stage glomerular epithelial cells (podocyte progenitors) adjacent to the vascular cleft where endothelial progenitors are subsequently recruited. Epithelial ephrin-B2 expression was accompanied by expression in endothelial and mesangial cells as capillary assembly progressed. At or near completion of glomerular maturation, epithelial ephrin-B2 expression was extinguished, with persistence in glomerular endothelial cells. Throughout development, one of several ephrin-B2 receptors, EphB4, was persistently and exclusively expressed in endothelial cells of venous structures. The findings show sequential ephrin-B2 expression across glomerular lineages, first in a distinct subset of podocyte progenitors and subsequently in endothelial cells of the developing glomerulus. Given targeting functions for Eph/ephrin family proteins, the findings suggest that ephrin-B2 expression marks podocyte progenitors at the site of vascular cleft formation, where expression may establish an "address" to which endothelial and mesangial progenitors are recruited. Thus, the present results suggest that ephrin-B2 and EphB interactions play an important role in glomerular microvascular assembly.

Animals↗

PubMed1994

CNTF, FGF, and NGF collaborate to drive the terminal differentiation of MAH cells into postmitotic neurons.

The differentiation of neuronal cell progenitors depends on complex interactions between intrinsic cellular programs and environmental cues. Such interactions have recently been explored using an immortalized sympathoadrenal progenitor cell line, MAH. These studies have revealed that depolarizing conditions, in combination with exposure to FGF, can induce responsiveness to NGF. Here we report that CNTF, which utilizes an intracellular signaling pathway distinct from that of both FGF and NGF, can collaborate with FGF to promote efficiently the differentiation of MAH progenitor cells to a stage remarkably reminiscent of NGF-dependent, postmitotic sympathetic neurons. We also find that similar collaborative interactions can occur during transdifferentiation of normal cultured chromaffin cells into sympathetic neurons.

Animals↗

PubMedDate not supplied

Multidimensional proteome analysis of human mammary epithelial cells.

Recent multidimensional liquid chromatography MS/MS studies have contributed to the identification of large numbers of expressed proteins for numerous species. The present study couples size exclusion chromatography of intact proteins with the separation of tryptically digested peptides using a combination of strong cation exchange and high resolution, reversed phase capillary chromatography to identify proteins extracted from human mammary epithelial cells (HMECs). In addition to conventional conservative criteria for protein identifications, the confidence levels were additionally increased through the use of peptide normalized elution times (NET) for the liquid chromatographic separation step. The combined approach resulted in a total of 5838 unique peptides identified covering 1574 different proteins with an estimated 4% gene coverage of the human genome, as annotated by the National Center for Biotechnology Information (NCBI). This database provides a baseline for comparison against variations in other genetically and environmentally perturbed systems. Proteins identified were categorized based upon intracellular location and biological process with the identification of numerous receptors, regulatory proteins, and extracellular proteins, demonstrating the usefulness of this application in the global analysis of human cells for future comparative studies.

Cell Line↗

PubMedDate not supplied

Development and evaluation of a micro- and nanoscale proteomic sample preparation method.

Challenges associated with the efficient and effective preparation of micro- and nanoscale (micro- and nanogram) clinical specimens for proteomic applications include the unmitigated sample losses that occur during the processing steps. Herein, we describe a simple "single-tube" preparation protocol appropriate for small proteomic samples using the organic cosolvent, trifluoroethanol (TFE) that circumvents the loss of sample by facilitating both protein extraction and protein denaturation without requiring a separate cleanup step. The performance of the TFE-based method was initially evaluated by comparisons to traditional detergent-based methods on relatively large scale sample processing using human breast cancer cells and mouse brain tissue. The results demonstrated that the TFE-based protocol provided comparable results to the traditional detergent-based protocols for larger, conventionally sized proteomic samples (>100 microg protein content), based on both sample recovery and numbers of peptide/protein identifications. The effectiveness of this protocol for micro- and nanoscale sample processing was then evaluated for the extraction of proteins/peptides and shown effective for small mouse brain tissue samples (approximately 30 microg total protein content) and also for samples of approximately 5000 MCF-7 human breast cancer cells (approximately 500 ng total protein content), where the detergent-based methods were ineffective due to losses during cleanup and transfer steps.

Animals↗

PubMedDate not supplied

Foot-mediated incubation: Nazca booby (Sula granti) feet as surrogate brood patches.

Incubation in most avian species involves transferring heat from parent to egg through a highly vascularized brood patch. Some birds, however, do not develop a brood patch. Unusual among birds, these species hold their eggs under the webs of their feet, but the role of the feet in heat transfer is uncertain. Often the webs are positioned between the feathered abdomen and the egg during incubation, suggesting that either the abdomen, the feet, or both could transfer heat to the egg. We studied heat transfer from foot webs to eggs during incubation in Nazca boobies by spatially separating the feet from the abdomen using an oversized egg. We found that feet transfer heat to eggs independently of any heat that may be transferred from the abdomen. In addition, we found that incubating boobies had significantly greater vascularization in their foot webs, measured as a percentage of web area covered by vessels, than nonincubating boobies. We also found that males, whether incubating or nonincubating, had significantly less web vascularization than females. We concluded that vascularized Nazca booby feet function in the same way during incubation that vascularized brood patches do, acting as surrogate brood patches.

Animals↗

PubMedDate not supplied

Management of unstable/acute slipped capital femoral epiphysis: results of a survey of the POSNA membership.

There is limited literature regarding the treatment of unstable slipped capital femoral epiphysis (SCFE). The Evidence Analysis Work Group (EAWG) initiated a questionnaire assessing management of unstable SCFE by the members of the Pediatric Orthopaedic Society of North America (POSNA). All members were surveyed by e-mail and fax. The survey was accessible through the POSNA web site. One third of the members responded. Seventy-three percent of members used the "stable/unstable" classification, while 27% used the "acute/chronic" terminology. Thirty-one percent of respondents felt that an unstable SCFE is an emergency, while 57% felt that treatment could be on an urgent (<8 hours) basis. Fifty-seven percent reported use of a single threaded screw for fixation for an unstable SCFE, and 40.3% recommended two threaded screws. There seems to be agreement on methods of patient evaluation, but discrepancies remain in classification and fixation methods. The EAWG recommends development of multicenter studies to evaluate the treatment of unstable SCFE.

Acute Disease↗

PubMedDate not supplied

Combined midfoot osteotomy for severe forefoot adductus.

A one-stage procedure combining a closing wedge osteotomy of the cuboid with an opening wedge of the medial cuneiform was used for the treatment of severe forefoot adductus. Results were reviewed in 33 patients (50 feet) followed-up for at least 2 years postoperatively. Clinical and radiographic improvement in forefoot position was achieved in 90% of cases. The mean calcaneo-second metatarsal angle improved from 37 degrees preoperatively to 18 degrees at final follow-up. The mean talo-first metatarsal angle improved from 15 degrees preoperatively to 3 degrees at final follow-up. The medial to lateral column ratio demonstrated 33% improvement after surgical treatment. Two feet were unimproved because of graft migration. Patients younger than age 5 years without a well-defined medial cuneiform ossific nucleus had a high rate of medial graft extrusion with loss of correction. This procedure should be reserved for patients aged 5 years or older. Ten patients followed-up for more than 6 years had no deterioration in results. This procedure provides effective, safe, predictable, and lasting correction of forefoot adductus.

Adolescent↗