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Articles by A Martin
Total Records ( 4 ) for A Martin
  B. S Peterson , M. N Potenza , Z Wang , H Zhu , A Martin , R Marsh , K. J Plessen and S. Yu

OBJECTIVE: The authors examined the effect of psychostimulants on brain activity in children and adolescents with ADHD performing the Stroop Color and Word Test. METHOD: The authors acquired 52 functional MRI scans in 16 youths with ADHD who were known responders to stimulant medication and 20 healthy comparison youths. Participants with ADHD were scanned on and off medication in a counterbalanced design, and comparison subjects were scanned once without medication. RESULTS: Stimulant medication significantly improved suppression of default-mode activity in the ventral anterior cingulate cortex in the ADHD group. When off medication, youths with ADHD were unable to suppress default-mode activity to the same degree as comparison subjects, whereas when on medication, they suppressed this activity to comparison group levels. Greater activation of the lateral prefrontal cortex when off medication predicted a greater reduction in ADHD symptoms when on medication. Granger causality analyses demonstrated that activity in the lateral prefrontal and ventral anterior cingulate cortices mutually influenced one another but that the influence of the ventral anterior cingulate cortex on the lateral prefrontal cortex was significantly reduced in youths with ADHD off medication relative to comparison subjects and increased significantly to normal levels when ADHD youths were on medication. CONCLUSIONS: Psychostimulants in youths with ADHD improved suppression of default-mode activity in the ventral anterior cingulate and posterior cingulate cortices, components of a circuit in which activity has been shown to correlate with the degree of mind-wandering during attentional tasks. Stimulants seem to improve symptoms in youths with ADHD by normalizing activity within this circuit and improving its functional interactions with the lateral prefrontal cortex.

  H Calkins , M. R Reynolds , P Spector , M Sondhi , Y Xu , A Martin , C. J Williams and I. Sledge

Background— Although radiofrequency catheter ablation (RFA) has evolved from an experimental procedure to an important treatment option for atrial fibrillation, the relative safety and efficacy of catheter ablation relative to that of antiarrhythmic drug (AAD) therapy has not been established.

Methods and Results— Two separate systematic reviews were conducted: one on RFA and the other on AAD to provide accurate and broadly representative estimates of the clinical efficacy and safety of both therapies in the treatment of atrial fibrillation. Electronic searches were conducted in EMBASE and MEDLINE from 1990 to 2007. For the RFA review, all study designs were accepted. For the AAD review, articles were limited to prospective studies on the following drugs of interest: amiodarone, dofetilide, sotalol, flecainide, and propafenone. Data were extracted by 1 reviewer, with a second reviewer performing independent confirmation of extracted data. Sixty-three RFA and 34 AAD studies were included in the reviews. Patients enrolled in RFA studies tended to be younger (mean age, 55 versus 62 years), had longer duration of atrial fibrillation (6.0 versus 3.1 years), and had failed a greater number of prior drug trials (2.6 versus 1.7). The single-procedure success rate of ablation off AAD therapy was 57% (95% CI, 50% to 64%), the multiple procedure success rate off AAD was 71% (95% CI, 65% to 77%), and the multiple procedure success rate on AAD or with unknown AAD usage was 77% (95% CI, 73% to 81%). In comparison, the success rate for AAD therapy was 52% (95% CI, 47% to 57%). A major complication of catheter ablation occurred in 4.9% of patients. Adverse events for AAD studies, although more common (30% versus 5%), were less severe.

Conclusions— Studies of RFA for treatment of atrial fibrillation report higher efficacy rates than do studies of AAD therapy and a lower rate of complications.

  A Martin , D Lang , S. T Hanke , S. J.X Mueller , E Sarnighausen , M Vervliet Scheebaum and R. Reski

Chloroplasts and bacterial cells divide by binary fission. The key protein in this constriction division is FtsZ, a self-assembling GTPase similar to eukaryotic tubulin. In prokaryotes, FtsZ is almost always encoded by a single gene, whereas plants harbor several nuclear-encoded FtsZ homologs. In seed plants, these proteins group in two families and all are exclusively imported into plastids. In contrast, the basal land plant Physcomitrella patens, a moss, encodes a third FtsZ family with one member. This protein is dually targeted to the plastids and to the cytosol. Here, we report on the targeted gene disruption of all ftsZ genes in P. patens. Subsequent analysis of single and double knockout mutants revealed a complex interaction of the different FtsZ isoforms not only in plastid division, but also in chloroplast shaping, cell patterning, plant development, and gravity sensing. These results support the concept of a plastoskeleton and its functional integration into the cytoskeleton, at least in the moss P. patens.

  D. W McCurdy , S Dibley , R Cahyanegara , A Martin and J. W. Patrick

Hexoses accumulate to high concentrations (~200 mM) in storage parenchyma cells of tomato fruit. Hexoses are sourced from the fruit apoplasm as hydrolysis products of phloem-imported sucrose. Three hexose transporters (LeHT1, LeHT2, LeHT3), expressed in fruit storage parenchyma cells, may contribute to hexose uptake by these cells. An analysis of their full-length sequences demonstrated that all three transporters belong to the STP sub-family of monosaccharide transporters that localize to plasma membranes. Heterologous expression of LeHT1 (and previously LeHT2, Gear et al., 2000), but not LeHT3, rescued a hexose transport-impaired yeast mutant when raised on glucose or fructose as the sole carbon source. Biochemically, LeHT1, similarly to LeHT2, exhibited transport properties consistent with a high-affinity glucose/H+ symporter. Significantly, LeHT1 and LeHT2 also functioned as low-affinity fructose/H+ symporters with apparent Km values commensurate with those of fruit tissues. A substantial reduction (80–90%) in fruit expression levels of all LeHT genes by RNAi-mediated knockdown caused a 55% decrease in fruit hexose accumulation. In contrast, photoassimilate production by source leaves and phloem transport capacity to fruit were unaffected by transporter knockdown. Collectively, these findings demonstrate that LeHTs play key roles in driving accumulation of hexoses into storage parenchyma cells during tomato fruit development.

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