Survey of the American Society of Neuroradiology Membership on the Use and Value of Intracranial Vessel Wall MRI

BACKGROUND AND PURPOSE

Intracranial vessel wall MR imaging is an emerging technique for intracranial vasculopathy assessment. Our aim was to investigate intracranial vessel wall MR imaging use by the American Society of Neuroradiology (ASNR) members at their home institutions, including indications and barriers to implementation.

MATERIALS AND METHODS

The ASNR Vessel Wall Imaging Study Group survey on vessel wall MR imaging use, frequency, applications, MR imaging systems and field strength used, protocol development approaches, vendor engagement, reasons for not using vessel wall MR imaging, ordering-provider interest, and impact on clinical care, was distributed to the ASNR membership between April 2 and August 30, 2019.

RESULTS

There were 532 responses; 79 were excluded due to nonresponse and 42 due to redundant institutional responses, leaving 411 responses. Fifty-two percent indicated that their institution performs vessel wall MR imaging, with 71.5% performed at least 1-2 times/month, most frequently on 3T MR imaging, and 87.7% using 3D sequences. Protocols most commonly included were T1-weighted pre- and postcontrast and TOF-MRA; 60.6% had limited contributions from vendors or were still in protocol development. Vasculopathy differentiation (94.4%), cryptogenic stroke (41.3%), aneurysm (38.0%), and atherosclerosis (37.6%) evaluation were the most common indications. For those not performing vessel wall MR imaging, interpretation (53.1%) or technical (46.4%) expertise, knowledge of applications (50.5%), or limitations of clinician (56.7%) or radiologist (49.0%) interest were the most common reasons. If technical/expertise obstacles were overcome, 56.4% of those not performing vessel wall MR imaging indicated that they would perform it. Ordering providers most frequently inquiring about vessel wall MR imaging were from stroke neurology (56.5%) and neurosurgery (25.1%), while 34.3% indicated that no providers had inquired.

CONCLUSIONS

More than 50% of neuroradiology groups use vessel wall MR imaging for intracranial vasculopathy characterization and differentiation, emphasizing the need for additional technical and educational support, especially as clinical vessel wall MR imaging implementation continues to grow.

Effects of sub-optimal illumination in plants. Comprehensive chlorophyll fluorescence analysis

The fluorescence signals emitted by chlorophyll molecules of plants is a promising non-destructive indicator of plant physiology due to its close link to photosynthesis. In this work, a deep photophysical study of chlorophyll fluorescence was provided, to assess the sub-optimal illumination effects on three plant species: L. sativa, A. hybridus and S. dendroideum. In all the cases, low light (LL) treatment induced an increase in pigment content. Fluorescence ratios - corrected by light reabsorption processes - remained constant, which suggested that photosystems stoichiometry was conserved. For all species and treatments, quantum yields of photophysical decay remained around 0.2, which meant that the maximum possible photosynthesis efficiency was about 0.8. L. sativa (C3) acclimated to low light illumination, displayed a strong increase in the LHC size and a net decrease in the photosynthetic efficiency. A. hybridus (C4) was not appreciably stressed by the low light availability whereas S. dendroideum (CAM), decreased its antenna and augmented the quantum yield of primary photochemistry. A novel approach to describe NPQ relaxation kinetics was also presented here and used to calculate typical deactivation times and amplitudes for NPQ components. LL acclimated L. sativa presented a much larger deactivation time for its state-transition-related quenching than the other species. Comprehensive fluorescence analysis allowed a deep study of the changes in the light-dependent reactions of photosynthesis upon low light illumination treatment.

Clinical, Imaging, and Lab Correlates of Severe COVID-19 Leukoencephalopathy

BACKGROUND AND PURPOSE

Patients infected with the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) can develop a spectrum of neurological disorders, including a leukoencephalopathy of variable severity. Our aim was to characterize imaging, lab, and clinical correlates of severe coronavirus disease 2019 (COVID-19) leukoencephalopathy, which may provide insight into the SARS-CoV-2 pathophysiology.

MATERIALS AND METHODS

Twenty-seven consecutive patients positive for SARS-CoV-2 who had brain MR imaging following intensive care unit admission were included. Seven (7/27, 26%) developed an unusual pattern of "leukoencephalopathy with reduced diffusivity" on diffusion-weighted MR imaging. The remaining patients did not exhibit this pattern. Clinical and laboratory indices, as well as neuroimaging findings, were compared between groups.

RESULTS

The reduced-diffusivity group had a significantly higher body mass index (36 versus 28 kg/m², P < .01). Patients with reduced diffusivity trended toward more frequent acute renal failure (7/7, 100% versus 9/20, 45%; P = .06) and lower estimated glomerular filtration rate values (49 versus 85 mL/min; P = .06) at the time of MRI. Patients with reduced diffusivity also showed lesser mean values of the lowest hemoglobin levels (8.1 versus 10.2 g/dL, P < .05) and higher serum sodium levels (147 versus 139 mmol/L, P = .04) within 24 hours before MR imaging. The reduced-diffusivity group showed a striking and highly reproducible distribution of confluent, predominantly symmetric, supratentorial, and middle cerebellar peduncular white matter lesions (P < .001).

CONCLUSIONS

Our findings highlight notable correlations between severe COVID-19 leukoencephalopathy with reduced diffusivity and obesity, acute renal failure, mild hypernatremia, anemia, and an unusual brain MR imaging white matter lesion distribution pattern. Together, these observations may shed light on possible SARS-CoV-2 pathophysiologic mechanisms associated with leukoencephalopathy, including borderzone ischemic changes, electrolyte transport disturbances, and silent hypoxia in the setting of the known cytokine storm syndrome that accompanies severe COVID-19.

Solubility Determination and Correlation of Warfarin Sodium 2‑Propanol Solvate in Pure, Binary, and Ternary Solvent Mixtures

The solubility of warfarin sodium isopropanol solvate (WS·IPA), a widely used anticoagulant, was determined at temperatures ranging from 278.15 to 333.15 K in four pure solvents (acetone, ethanol, IPA, and water), five binary solvent mixtures (IPA + acetone, IPA + ethanol, IPA + water, IPA + heptane, and IPA + hexane), and five ternary solvent mixtures (IPA + acetone + heptane, IPA + acetone + hexane, IPA + ethanol + heptane, IPA + ethanol + hexane, and IPA + water + heptane) using the polythermal method. It was demonstrated that the solubility of WS·IPA increases with increasing temperature in the pure solvents and at constant solvent composition in the solvent mixtures. In addition, the solubility of WS·IPA in IPA increases with increasing content of acetone, ethanol, and water, which act as cosolvents, and decreases with increasing content of heptane and hexane, which act as antisolvents. The experimental solubility data of WS·IPA in pure solvents and binary and ternary solvent mixtures were correlated using the modified Apelblat and λh model equations. The correlated solubility data agree with the experimental data based on the relative deviation and the average relative deviation (ARD %) values. Thus, the correlated and experimentally derived solubility data of WS·IPA provide a pathway to engineer advanced pharmaceutical crystallization processes for WS·IPA.

Effect of CTA Tube Current on Spot Sign Detection and Accuracy for Prediction of Intracerebral Hemorrhage Expansion

BACKGROUND AND PURPOSE

Reduction of CT tube current is an effective strategy to minimize radiation load. However, tube current is also a major determinant of image quality. We investigated the impact of CTA tube current on spot sign detection and diagnostic performance for intracerebral hemorrhage expansion.

MATERIALS AND METHODS

We retrospectively analyzed a prospectively collected cohort of consecutive patients with primary intracerebral hemorrhage from January 2001 to April 2015 who underwent CTA. The study population was divided into 2 groups according to the median CTA tube current level: low current (<350 mA) and high current (≥350 mA). CTA first-pass readings for spot sign presence were independently analyzed by 2 readers. Baseline and follow-up hematoma volumes were assessed by semiautomated computer-assisted volumetric analysis. Sensitivity, specificity, positive and negative predictive values, and accuracy of spot sign in predicting hematoma expansion were calculated.

RESULTS

This study included 709 patients (288 and 421 in the low- and high-current groups, respectively). A higher proportion of low-current scans identified at least 1 spot sign (20.8% versus 14.7%, P = .034), but hematoma expansion frequency was similar in the 2 groups (18.4% versus 16.2%, P = .434). Sensitivity and positive and negative predictive values were not significantly different between the 2 groups. Conversely, high-current scans showed superior specificity (91% versus 84%, P = .015) and overall accuracy (84% versus 77%, P = .038).

CONCLUSIONS

CTA obtained at high levels of tube current showed better diagnostic accuracy for prediction of hematoma expansion by using spot sign. These findings may have implications for future studies using the CTA spot sign to predict hematoma expansion for clinical trials.

Efficacy and safety of switching to abacavir/lamivudine (ABC/3TC) plus rilpivirine (RPV) in virologically suppressed HIV-infected patients on HAART

We analysed the efficacy and safety of switching from a regimen based on nonnucleoside reverse transcriptase inhibitors (NNRTI) or integrase inhibitors (INI) to ABC/3TC + RPV in virologically suppressed HIV-infected patients. This multicentre, retrospective study comprised asymptomatic HIV-infected patients who switched from 2 NRTI + NNRTI or 2 NRTI + INI to ABC/3TC + RPV between February 2013 and December 2013; all had undetectable HIV viral load prior to switching. Efficacy and safety, and changes in lipids and cardiovascular risk (CVR) were analysed at 48 weeks. Of 85 patients (74.1 % men, mean age 49.5 years), 83 (97.6 %) switched from a regimen based on NNRTI (EFV 74, RPV 5, ETV 2, NVP 2), and 45 (53 %) switched from TDF/FTC to ABC/3TC. The main reasons for switching were toxicity (58.8 %) and convenience (29.4 %). At 48 weeks, 78 (91.8 %) patients continued taking the same regimen; efficacy was 88 % by intention to treat, and 96 % by per protocol. Two patients were lost to follow-up and five ceased the new regimen (4 due to adverse effects and 1 virologic failure). Mean CD4 cell counts increased (744 vs. 885 cells/μL; p = 0.0001), and there were mean decreases in fasting total cholesterol (-15.9 mg/dL; p < 0.0001) and LDL-cholesterol (-11.0 mg/dL; p < 0.004), with no changes in HDL-cholesterol, triglycerides, total cholesterol:HDL-cholesterol ratio, and CVR. ABC/3TC + RPV is effective and safe in virologically-suppressed patients on antiretroviral therapy (ART). Forty-eight weeks after switching the lipid profile improved with decreases in total and LDL cholesterol.

Sensitivity of visual and quantitative detection of middle cerebral artery occlusion on non-contrast-enhanced computed tomography

INTRODUCTION

This study aims to investigate diagnostic sensitivity and reliability for the detection of middle cerebral artery occlusion (MCAO) on non-contrast-enhanced computed tomography (NECT) by visual assessment (VA), Hounsfield unit (HU) measurement, calculation of the Hounsfield unit/hematocrit (HU/Hct) ratio, and combination of visual assessment and attenuation measurement (VA + HU).

METHODS

NECT of 18 patients with angiographically proven MCAO and 18 patients without MCAO were reviewed by two blinded observers. Visual assessment of presence or absence of a hyperdense sign was followed by HU measurement of both middle cerebral arteries (MCA). Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for VA, HU measurement, HU/Hct ratio, and VA + HU measurement. Receiver operating characteristic curve analysis (ROC) was performed to determine the optimal cut-off values for MCAO using attenuation measurements or HU/Hct ratio.

RESULTS

Diagnostic sensitivity/specificity was 63%/91% for VA, 56%/88% for attenuation measurement, 68 %/81 % for HU/Hct ratio, and 75%/78% for VA + HU. ROC curve analysis revealed cut-off values of >42.5 HU for attenuation measurements and >1.12 HU/Hct for HU/Hct ratio.

CONCLUSION

Combination of visual assessment with additional attenuation measurement with a cut-off value of 42.5 HU is recommended for most sensitive and reliable detection of MCAO on NECT.

Comparative effectiveness research

The goal of comparative effectiveness research is to improve health care while dealing with the seemingly ever-rising cost. An understanding of comparative effectiveness research as a core topic is important for neuroradiologists. It can be used in a variety of ways. Its goal is to look at alternative methods of interacting with a clinical condition, ideally, while improving delivery of care. While the Patient-Centered Outcome Research initiative is the most mature US-based foray into comparative effectiveness research, it has been used more robustly in decision-making in other countries for quite some time. The National Institute for Health and Clinical Excellence of the United Kingdom is a noteworthy example of comparative effectiveness research in action.

Contrast extravasation on CT angiography predicts hematoma expansion and mortality in acute traumatic subdural hemorrhage

BACKGROUND AND PURPOSE

The presence of active contrast extravasation at CTA predicts hematoma expansion and in-hospital mortality in patients with nontraumatic intracerebral hemorrhage. This study aims to determine the frequency and predictive value of the contrast extravasation in patients with aSDH.

MATERIALS AND METHODS

We retrospectively reviewed 157 consecutive patients who presented to our emergency department over a 9-year period with aSDH and underwent CTA at admission and a follow-up NCCT within 48 hours. Two experienced readers, blinded to clinical data, reviewed the CTAs to assess for the presence of contrast extravasation. Medical records were reviewed for baseline clinical characteristics and in-hospital mortality. aSDH maximum width in the axial plane was measured on both baseline and follow-up NCCTs, with hematoma expansion defined as >20% increase from baseline.

RESULTS

Active contrast extravasation was identified in 30 of 199 discrete aSDHs (15.1%), with excellent interobserver agreement (κ = 0.80; 95% CI, 0.7-0.9). The presence of contrast extravasation indicated a significantly increased risk of hematoma expansion (odds ratio, 4.5; 95% CI, 2.0-10.1; P = .0001) and in-hospital mortality (odds ratio, 7.6; 95% CI, 2.6-22.3; P = 0.0004). In a multivariate analysis controlled for standard risk factors, the presence of contrast extravasation was an independent predictor of aSDH expansion (P = .001) and in-hospital mortality (P = .0003).

CONCLUSIONS

Contrast extravasation stratifies patients with aSDH into those at high risk and those at low risk of hematoma expansion and in-hospital mortality. This distinction could affect patient treatment, clinical trial selection, and possible surgical intervention.

SCORE-IT: the Spot Sign score in restricting ICH growth─an Atach-II ancillary study

INTRODUCTION

The ATACH-II trial is designed to evaluate whether intensive blood pressure reduction can reduce hematoma growth and improve outcome. However, it is difficult to determine, at presentation, which patients are at highest risk of ongoing bleeding, and will receive the most clinical benefit from blood pressure therapy. It may be that improved predictive markers will lead to efficient, personalized selection of optimal therapy. We hypothesize that specific imaging findings on CT angiography (CTA) and MRI will mark those patients who receive the most benefit from intensive blood pressure reduction.

METHODS

Many patients enrolled in ATACH-II will undergo CTA and/or MRI as part of routine clinical care. We will perform a blinded analysis of these images. For CTA, we will determine the presence of contrast pooling (also termed contrast extravasation or the "Spot Sign"). In addition, we will calculate a Spot Sign Score, a score that includes number of Spot Signs, diameter, and contrast density. For MRI, we will focus on the presence, number, and location of cerebral microbleeds (CMBs) on sensitive T2*-weighted MRI sequences.

RESULTS

We will test the hypothesis that patients with a Spot Sign will receive clinical benefit from intensive blood pressure reduction. In addition, we will determine whether patients with the highest Spot Sign Scores receive the most benefit from intensive blood pressure reduction. Finally, we will determine whether the absence of CMBs marks those at higher risk for hematoma expansion, and therefore more likely to benefit from treatment.

CONCLUSION

This ancillary study offers the tremendous opportunity to determine whether imaging findings can risk stratify ICH patients for acute therapies aimed at limiting hematoma growth.

Frequency of adequate contrast opacification of the major intracranial venous structures with CT angiography in the setting of intracerebral hemorrhage: comparison of 16- and 64-section CT angiography techniques

BACKGROUND AND PURPOSE

DVST is an important cause of ICH because its treatment may require anticoagulation or mechanical thrombectomy. We aimed to determine the frequency of adequate contrast opacification of the major intracranial venous structures in CTAs performed for ICH evaluation, which is an essential factor in excluding DVST as the ICH etiology.

MATERIALS AND METHODS

Two readers retrospectively reviewed CTAs performed in 170 consecutive patients with ICH who presented to our emergency department during a 1-year period to determine by consensus whether qualitatively, contrast opacification in each of the major intracranial venous structures was adequate to exclude DVST. "Adequate contrast opacification" was defined as homogeneous opacification of the venous structure examined. "Inadequate contrast opacification" was defined as either inhomogeneous opacification or nonopacification of the venous structure examined. Delayed scans, if obtained, were reviewed by the same readers blinded to the first-pass CTAs to determine the adequacy of contrast opacification in the venous structures according to the same criteria. In patients who did not have an arterial ICH etiology, the same readers determined if thrombosis of an inadequately opacified intracranial venous structure could have potentially explained the ICH by correlating the presumed venous drainage path of the ICH with the presence of inadequate contrast opacification within the venous structure draining the venous territory of the ICH. CTAs were performed in 16- or 64-section CT scanners with bolus-tracking, scanning from C1 to the vertex. Patients with a final diagnosis of DVST were excluded. We used the Pearson χ(2) test to determine the significance of the differences in the frequency of adequate contrast opacification within each of the major intracranial venous structures in scans obtained using either a 16- or 64-section MDCTA technique.

RESULTS

Fifty-eight patients were evaluated with a 16-section MDCTA technique (34.1%) and 112 with a 64-section technique (65.9%). Adequate contrast opacification within all major noncavernous intracranial venous structures was significantly less frequent in first-pass CTAs performed with a 64-section technique (33%) than in those performed with a 16-section technique (60%, P value < .0001). Delayed scans were obtained in 50 patients, all of which demonstrated adequate contrast opacification in the major noncavernous intracranial venous structures. In 142 patients with supratentorial or cerebellar ICH without an underlying arterial etiology, we found that thrombosis of an inadequately opacified major intracranial venous structure could have potentially explained the ICH in 38 patients (26.8%), most examined with a 64-section technique (86.8%).

CONCLUSIONS

Inadequate contrast opacification of the major intracranial venous structures is common in first-pass CTAs performed for ICH evaluation, particularly if performed with a 64-section technique. Acquiring delayed scans appears necessary to confidently exclude DVST when there is strong clinical or radiologic suspicion.

Practical scoring system for the identification of patients with intracerebral hemorrhage at highest risk of harboring an underlying vascular etiology: the Secondary Intracerebral Hemorrhage Score

BACKGROUND AND PURPOSE

An ICH patient's risk of harboring an underlying vascular etiology varies according to baseline clinical and NCCT characteristics. Our aim was to develop a practical scoring system to stratify patients with ICH according to their risk of harboring a vascular etiology.

MATERIALS AND METHODS

Using a data base of 623 patients with ICH evaluated with MDCTA during a 9-year period, we developed a scoring system based on baseline clinical characteristics (age group [0-2 points], sex [0-1 point], neither known HTN nor impaired coagulation [0-1 point]), and NCCT categorization (0-2 points) to predict the risk of harboring a vascular lesion as the ICH etiology (SICH score). We subsequently applied the SICH score to a prospective cohort of 222 patients with ICH who presented to our emergency department during a 13-month period. Using ROC analysis, we calculated the AUC and MOP for the SICH score in both the retrospective and prospective patient cohorts separately and the entire patient population. Patients with SAH in the basal cisterns were excluded.

RESULTS

A vascular etiology was found in 120 of 845 patients with ICH evaluated with MDCTA (14.2%), most commonly AVMs (45.8%), aneurysms with purely intraparenchymal rupture (21.7%), and DVSTs (16.7%). The MOP was reached at a SICH score of >2, with the highest incidence of vascular ICH etiologies in patients with SICH scores of 3 (18.5%), 4 (39%), 5 (84.2%), and 6 (100%). There was no significant difference in the AUC between both patient cohorts (0.86-0.87).

CONCLUSIONS

The SICH score successfully predicts a given ICH patient's risk of harboring an underlying vascular etiology and could be used as a guide to select patients with ICH for neurovascular evaluation to exclude the presence of a vascular abnormality.

An Atlas of Infectious and Parasitic Diseases of the Central Nervous System. A Cooperative Study of SILAN (Sociedad Iberolatinoamericana de Neurorradiologia)

Infectious diseases of the central nervous system vary in frequency in different locations in America and Europe. What is common in Brazil can be a sporadic presentation in Europe. Cooperative work gathering experiences from neuroradiologists working in various places can be achieved and will help to identify uncommon cases that can present in our daily practice.

[Usefulness of hyperbaric oxygen in the treatment of radionecrosis and symptomatic brain edema after LINAC radiosurgery]

Radionecrosis with brain edema is a complication of radiosurgery. Three female patients harbouring a frontal pole, petrous and parasagital parietoocipital meningiomas respectively who had been treated with LINAC radiosurgery are presented. Those patients developed, between two and eight months later, a severe symptomatic radionecrosis with a huge brain edema resistant to the usual steroid therapy. Only after 40 sessions of hyperbaric oxygen, a good remission of the lesions was obtained. There are few cases reported in the literature with such a good outcome. Consequentely, this therapy must be taken into account to treat this type of radiosurgical complication before considering surgery.

Diagnostic accuracy and yield of multidetector CT angiography in the evaluation of spontaneous intraparenchymal cerebral hemorrhage

BACKGROUND AND PURPOSE

Multidetector CT angiography (MDCTA) is emerging as the favored initial diagnostic examination in the evaluation of patients presenting with spontaneous intraparenchymal hemorrhage (IPH). This study aims to evaluate the diagnostic accuracy and yield of MDCTA for the detection of vascular etiologies in adult patients presenting to the emergency department with IPH.

MATERIALS AND METHODS

We conducted a retrospective study of 623 consecutive adult patients presenting to the emergency department with IPH, who were evaluated with MDCTA during a 9-year period. CT angiograms were reviewed by 2 neuroradiologists to determine the IPH site and the presence of a vascular etiology. Patients with associated subarachnoid hemorrhage in the basal cisterns were excluded from the study. Medical records were reviewed for risk factors and correlation with final diagnosis. The diagnostic accuracy of MDCTA compared with conventional angiography, intraoperative evaluation, and pathologic findings was determined, when available. Multiple-variable logistic regression analysis was performed to determine clinical and radiologic factors that predict a higher yield of MDCTA.

RESULTS

MDCTA demonstrated a vascular etiology in 91 patients (14.6%), with a sensitivity of 96%, specificity of 99%, and diagnostic accuracy of 98%. We found independent, statistically significant higher yields of MDCTA in patients with the following characteristics: 1) age younger than 46 years (47%); 2) lobar (20%) or infratentorial (16%) IPH, especially lobar IPH with associated intraventricular hemorrhage (25%); 3) female sex (18%); or 4) neither known hypertension nor impaired coagulation at presentation (33%).

CONCLUSIONS

MDCTA is an accurate diagnostic examination in the evaluation of adult patients presenting with spontaneous IPH and should be performed in all patients with the aforementioned clinical and radiologic characteristics.

Contrast-enhanced MR angiography is not more accurate than unenhanced 2D time-of-flight MR angiography for determining > or = 70% internal carotid artery stenosis

BACKGROUND AND PURPOSE

Internal carotid artery (ICA) atheromatous disease is an important cause of ischemic stroke, and endarterectomy or stent placement is typically indicated for symptomatic patients with > or = 70% stenosis. Our purpose was to compare contrast-enhanced MR angiography (CE-MRA) with unenhanced 2D time-of-flight MR angiography (2D TOF MRA) in detecting hemodynamically significant ICA stenosis, by using CT angiography (CTA) as the reference standard.

MATERIALS AND METHODS

This was an institutional review board-approved retrospective study. We identified 177 consecutive patients (354 ICAs) who received correlative CE-MRA, 2D TOF MRA, and CTA. Two neuroradiologists blinded to the CTA data graded the degree of ICA stenosis according to a 5-point scale. Additionally, luminal signal-intensity characteristics including 1) signal intensity drop-out, 2) distal-vessel narrowing, and 3) distal-vessel signal-intensity reduction were recorded. MRA results were correlated with those of CTA, and receiver-operating-characteristic (ROC) curves were constructed.

RESULTS

On CTA, there were 55 ICAs with and 299 without > or = 70% stenosis. CE-MRA was 84% sensitive and 96% specific for detecting > or = 70% stenosis; 2D TOF MRA was 80% sensitive and 95% specific. The area under the ROC curve was 0.97 for CE-MRA and 0.95 for 2D TOF MRA (P = .51, not significant). For both MRA studies, each of the luminal signal-intensity characteristics had high specificity (> 98%) but poor-to-mild sensitivity (35%-66%) in detecting > or = 70% stenosis.

CONCLUSIONS

Although it is established that CE-MRA more accurately delineates neurovascular anatomy than does unenhanced 2D TOF MRA, the administration of gadolinium did not offer a significant advantage in distinguishing surgically treatable ICA stenosis. This conclusion may be important in patients with contraindications to gadolinium.

Spectroscopic study of the dispiro-1,2,4,5-tetroxane (cyclohexanone diperoxide)

The aim of this work is to present results derived from experimental IR and UV spectra and theoretical studies of DPCH, in order to get a more deeper insight on the physicochemical properties of this compound to gain a more deep knowledge of its action, helping in the design of new compounds with antimalaric effects. Experimental results are analyzed on the basis of theoretical calculations, which allow to derive suitable interpretations of spectral data.

Gene transduction of an active mutant of akt exerts cytoprotection and reduces graft injury after liver transplantation

Akt is expected to be an effective target for the treatment of ischemia-reperfusion injury (I/R) due to its anti-apoptotic properties and its ability to activate the endothelial nitric oxide synthase (eNOS) enzyme. Therefore, this study was aimed to determine the efficacy of an active mutant of Akt (myr-Akt) to decrease I/R injury in a model of orthotopic liver transplantation in pigs. In addition, we analyzed the contribution of nitric oxide in the Akt-mediated effects by using an eNOS mutant (S1179DeNOS) that mimics the phosphorylation promoted by Akt in the eNOS sequence. Donors were treated with adenoviruses codifying for myr-Akt, S1179DeNOS or beta-galactosidase 24 h before liver harvesting. Then, liver grafts were orthotopically transplanted into their corresponding recipients. Levels of transaminases and lactate dehydrogenase (LDH) increased in all recipients after 24 h of transplant. However, transaminases and LDH levels were significantly lower in the myr-Akt group compared with vehicle. The percentage of apoptotic cells and the amount of activated-caspase 3 protein were also markedly reduced in myr-Akt-treated grafts after 4 days of liver transplant compared with vehicle and S1179DeNOS groups. In conclusion, myr-Akt gene therapy effectively exerts cytoprotection against hepatic I/R injury regardless of the Akt-dependent eNOS activation.

Analysis of the expression of HLA class I, proinflammatory cytokines and chemokines in primary tumors from patients with localized and metastatic renal cell carcinoma

Changes in the human leukocyte antigen (HLA) class I expression and cytokine and chemokine production both by cancer cells and by normal surrounding tissue are believed to be responsible for immune escape and tumor progression. In this study, we compared the tumor expression levels of HLA heavy chain (HLAhc), beta-2-microglobulin (beta2m), chemokines (Interferon-gamma-inducible Protein-10 (IP-10), Interferon-inducible T-cell Alpha-Chemoattractant (I-TAC), Stromal cell-Derived Factor-1 (SDF-1), Macrophage Inflammatory Protein-1-alpha (MIP-1-alpha) and Regulated upon Activation, Normally T-Expressed, and presumably Secreted (RANTES)) and cytokines (Vascular Endothelial Growth Factor (VEGF), Interferon-gamma (IFN-gamma), Interleukin-10 (IL-10), Tumor Growth Factor-beta (TGB-beta)) in primary tumors and adjacent normal tissues from patients with localized and metastatic renal cell carcinoma (RCC) using a quantitative real-time polymerase chain reaction technique. We report that the expression of HLAhc, beta2m and the studied cytokines and chemokines (except for SDF-1) was significantly higher in the tumor (29 samples) than in the normal tissue (14 samples). When we compared the tumor expression levels between patients with localized RCC and patients with advanced metastatic stage, we found that the messenger RNA expression levels of HLAhc and beta2m were much lower in patients with metastatic RCC (6 cases) than in patients with localized cancer (23 cases), with levels similar to those in normal tissue. This was also confirmed on a protein level by immunohistological labeling of tumor tissues. Thirty-nine percent of the analyzed RCC tumors showed partial loss of HLA class I molecules, while 6% of the tumors showed HLA class I total loss. The expression of IP-10, SDF-1 and VEGF-c was also significantly lower in patients with advanced tumor, while the IFN-gamma expression in metastatic RCC was not detectable. Our findings show that primary RCC tumors are characterized by a high expression of HLAhc and a presence of proinflammatory mediators and chemokines. We also observed that disease progression and development of metastasis in RCC are associated with decreased expression of HLAhc, beta2m, IP-10, SDF-1 and IFN-gamma. This microenvironment may suppress the cytotoxic response, creating conditions that favor tumor escape and cancer progression.

Experimental preparation and UV/IR spectroscopic characterization of 1,3-dibutanal-1,2,4,5-tetroxane

We report the experimental preparation of the 1,3-butanal-1,2,4,5-tetroxane by oxidation of glutataldehyde with oxygen peroxide in presence of concentrated sulfuric acid, following the Bayer and Viller method modified by Jorge et al. The UV and IR spectra are studied from the experimental and theoretical standpoint. A rather complete vibrational assignment was performed and the nature of the electronic transitions was discussed in detail.

Comparison of the SYBR Green and the hybridization probe format for real-time PCR detection of HHV-6

A comparative study was conducted of a novel real-time quantitative PCR test (LightCycler System) with FastStart DNA Master(PLUS) SYBR Green I dye to detect DNA of human herpes virus 6 (HHV-6). Results were compared with those of a real-time quantitative PCR with hybridization probe (HP) formats using the fluorescence resonance energy transfer method, and with those of a single qualitative PCR test. The detection limit of the test with SYBR Green I dye was 20 copies of the virus, similar to that of the other two tests. The reproducibility was satisfactory. The new test has the same advantages as real-time PCR with HP formats and offers a greater versatility at lower cost.

Calorimetric and computational study of enthalpy of formation of 3,6-dibutanoic-1,2,4,5-tetroxane

A thermochemical a rather simple experimental technique method, is used to determine the enthalpy of the formation of 3,6-dibutanoic-1,2,4,5-tetroxane. The study is complemented with suitable theoretical calculations at the semiempirical and ab initio levels. A particular satisfactory agreement between both ways is found for the ab initio calculation at the 6-311G basis set level. Some possible extensions of the present procedure are pointed out.

Phylogenetic characterization of a corrosive consortium isolated from a sour gas pipeline

Biocorrosion is a common problem in oil and gas industry facilities. Characterization of the microbial populations responsible for biocorrosion and the interactions between different microorganisms with metallic surfaces is required in order to implement efficient monitoring and control strategies. Denaturing gradient gel electrophoresis (DGGE) analysis was used to separate PCR products and sequence analysis revealed the bacterial composition of a consortium obtained from a sour gas pipeline in the Gulf of Mexico. Only one species of sulfate-reducing bacteria (SRB) was detected in this consortium. The rest of the population consisted of enteric bacteria with different characteristics and metabolic capabilities potentially related to biocorrosion. Therefore, several types of bacteria may be involved in biocorrosion arising from natural biofilms that develop in industrial facilities. The low abundance of the detected SRB was evidenced by environmental scanning electron microscopy (ESEM). In addition, the localized corrosion of pipeline steel in the presence of the consortium was clearly observed by ESEM after removing the adhered bacteria.

[Cotard's delusion of negations]

The authors report a clinical case of a sixty-two-year-old woman admitted to hospital because Cotard's nihilistic delusion in a one year major depressive episode. The patient was treated with clomipramine and olanzapine with a rapid improvement and normalisation of humor and delusions.

Basilar and middle cerebral artery reserve: a comparative study using transcranial Doppler and breath-holding techniques

BACKGROUND AND PURPOSE

A 1997 report suggests that the posterior circulation of the normal brain has diminished vasoreactivity compared with the anterior circulation. To further study this, we quantified and compared the vasodilatory capacities of the middle cerebral (MCA) and basilar artery (BA) territories in response to changes in PaCO(2), as indices of respective cerebrovascular reserve (CVR). If posterior circulation CVR is indeed physiologically lower than that of the MCA, it might indicate a greater risk of low-flow ischemia distal to basilar obstructive cerebrovascular lesions and provide a rationale for earlier treatment of such lesions with interventional techniques. We also wished to establish normal baseline CVR values for the posterior circulation.

METHODS

Twelve patients with signs and/or symptoms suggestive of posterior circulation disease but without flow-limiting obstructive changes and 11 normal controls were entered into the study. With the use of transcranial Doppler techniques, alterations in blood flow velocity in response to sequential breath-holding trials of varying duration were simultaneously monitored in both MCAs and the BA. CVR was measured as the percent velocity increase (during breath-holding) from resting baseline values.

RESULTS

No significant differences were found in CVR between the MCA and BA territories in or between patients and controls.

CONCLUSIONS

Our study suggests that the anterior and posterior circulations have similar reserve capacities in individuals without flow-limiting cerebrovascular obstructive lesions and that the BA territory, relative to the MCA territory, is not at increased risk for low-flow stroke on the basis of limited reserve potential.

Inactivation and thermal stabilization of glycogenin by linked glycogen

Glycogen-free but not glycogen-bound glycogenin transglucosylates dodecyl-beta-maltoside. Furthermore, its sugar nucleotide-binding site can be photoaffinity labeled using [beta-(32)P]5-azido-UDP-glucose. Disruption with DMSO of the hydrogen bonds that stabilize the alpha-helical structure of glycogen restored the photoaffinity labeling of the glycogen-bound enzyme but not its transglucosylation activity. The larger size polysaccharide that linked to glycogenin allowed transglucosylation corresponding to that of PG-200, a proteoglycogen species of M(r) 200 kDa. PG-200 showed lower activity and increased activation energy than glycogen-free glycogenin. Heat denaturation of glycogen-free and glycogen-bound glycogenin occurred at 51 and 64 degrees C, respectively. Active glycogenin was recovered after the glycogen-bound form was heated at 60-70 degrees C and immediately cooled. Treatment at 60 degrees C of the glycogen-free enzyme resulted in inactivation. This is the first report describing the inactivation and thermal stabilization of an enzyme by linked polysaccharide.

Three-dimensional ultrasound for the measurement of choroidal melanomas

OBJECTIVE

To evaluate the reliability of 3-dimensional ultrasound (3D-US) for the measurement of choroidal melanomas.

DESIGN

Retrospective case series.

PARTICIPANTS

Forty-two consecutive cases of choroidal melanoma imaged with 3D-US.

METHODS

Tumor measurements obtained with ophthalmoscopy, transillumination, standard ultrasound techniques, 3D-US, and pathological studies. Tumor diameters, heights, and volumes were compared. Our 3D-US tumor measurement techniques were tested for intraobserver and interscan reproducibility.

RESULTS

Fifty 3D-US images were studied. The 3D-US tumor measurements were found to be reproducible (height coefficient of variation [CV] < or = 3%; diameter CV < or = 9.7%; volume CV < or = 13.2%). There was significant correlation with the usual methods of tumor measurement (diameter r = 0.76; height r > or = 0.98). Significant differences were found between measurements at pathological examination, as compared with both 2-dimensional and 3D-US height measurements (range, 0.73-0.83 mm). This finding was thought to be due to specimen shrinkage. Three-dimensional ultrasound was found to be at least as reproducible as clinical examination and standard ultrasound techniques used for measurement of diameter and height of choroidal melanomas. It was our impression that the 3D-US volume measurements accounted for the geometry of the tumor better than volume estimates calculated from basal area and tumor height.

CONCLUSIONS

Three-dimensional ultrasound measurements of choroidal melanoma were reproducible, correlated well with other tumor measurement techniques, and can be used for measurement of choroidal melanomas.

Complications and re-operation rate after tension-band wiring of olecranon fractures

Tension-band wire fixation of olecranon fractures leads to a high re-operation rate because of the need to remove the metalware. This problem has commonly been thought to be related mainly to the backing-out of the Kirschner wires. A retrospective study was carried out in 55 patients with displaced olecranon fractures operated on with the tension-band wiring technique, in whom there was an overall 71.7% re-operation rate. Complications were few and minor in most patients. The main reason for the removal of the metalware was a direct complaint from the patient (in 61.3% of all removals). A literature review analyzing the causes of metalware removal is also presented.

Plaque-mounted diode-light transillumination for localization around intraocular tumors

OBJECTIVE

To evaluate the usefulness of plaque-mounted diode-light transillumination (DLT) for the localization of episcleral plaques around intraocular tumors.

METHODS

A clinical case series was performed to create, evaluate, and modify diode-light plaque construction, application, and imaging. Eight patients with choroidal melanoma were offered DLT as an additional method of ophthalmic plaque localization. Plaques were constructed by affixing non-heat-producing, light-emitting diodes with their apertures flush with the episcleral outer surface of the rim of the plaque. A bioimplantable epoxy was used to encapsulate the electronic components. Radioactive DLT eye plaques were sewn to the episclera to cover the base of the intraocular tumors; then diode lights were illuminated, viewed, and recorded. Thus, DLT was used to photographically document the relative position of the eye plaque covering the tumor base. The use of DLT also permitted a subjective evaluation of the contact (plaque contact) of each light with the sclera.

RESULTS

Still and video images of plaque-mounted diode retro-transillumination were obtained, and no evidence of toxic effects of diode light were noted.

CONCLUSIONS

Small posterior melanomas are difficult to visualize with standard transillumination techniques and are associated with poor local control. To improve and document plaque placement, we developed plaque-mounted diode lights for retrobulbar transillumination. This technique provides unique photographic documentation of episcleral plaque localization beneath intraocular tumors.

Three-dimensional ultrasonography of choroidal melanoma: extrascleral extension

PURPOSE

To describe the results of three-dimensional ultrasonography used to evaluate extrascleral extension of a choroidal melanoma.

METHODS

Case report. The three-dimensional ultrasound system uses a 10-MHz B-mode transducer combined with a motorized rotating holder. The system acquires 180 sequential images that are stored and processed to create a three-dimensional block of the region of interest.

RESULTS

Unique coronal and oblique perspectives were obtained from interactive manipulation of the three-dimensional reconstruction. Examination of the three-dimensional image allowed us to detect the transscleral uveal-orbital connection. Extrascleral melanomatous extension was confirmed on histopathologic examination.

CONCLUSION

Three-dimensional ultrasonography is a promising imaging technique for evaluating melanomatous extrascleral extension.

[Cervical metastasis of choriocarcinoma]

Neck metastatic adenopathy involves to set off a protocol aiming to specify the growth's origin. Complete ENT-examination facing a hard, movable, laterocervical lump is compulsory. Lacking the primary next comes fine needle biopsy and if it's not clear enough a cervicotomy must be performed. We report the diagnosis, the treatment and the follow-up of a testicle choriocarcinoma case, diagnosed through neck biopsy. Perusal of the bibliography.

[Neuroendocrine carcinoma of the larynx. Review of literature in reference to one case report]

Neuroendocrin tumors are unusual neoplasies, even more within the ENT-sphere. Report of 1 case treated in our Service. Review of immunohistochemical criteria with the aim of achieving the diagnosis. Some bibliographical series are analyzed with the target to pick up the treatment of these uncommon growths.

Salmonella typhi Ty2 OmpC porin induces bactericidal activity on U937 monocytes

The immunogenic effect of Salmonella typhi OmpC porin during typhoid fever in humans was evaluated in vitro. Peripheral blood mononuclear cells from 17 patients were challenged with outer membrane preparations from Escherichia coli UH302 and UH302/pSTP2K2 strains, both lacking E. coli OmpF and OmpC porins, although UH302/pSTP2K2 expressed a plasmid-encoded S. typhi Ty2 OmpC. The mononuclear cell supernatants, immunized in vitro with OmpC antigen, derived from 10 out of 17 patients activated U937 bactericidal capacity. In contrast, the supernatants from the immunization with outer membrane preparation lacking S. typhi Ty2 OmpC induced a significantly reduced bactericidal capacity of U937 cells. This procedure should prove useful for in vitro characterization of cellular immunogens from exclusive human pathogens.

Three-dimensional ultrasonography of choroidal melanoma: localization of radioactive eye plaques

OBJECTIVE

To evaluate the use of 3-dimensional (3D) ultrasonography for the localization of episcleral eye plaques during the treatment of choroidal melanomas.

METHODS

A series of 13 patients with choroidal melanoma were treated with radioactive palladium 103 seeds affixed into gold eye plaques. During surgery, 3D ultrasonography was performed with a commercially available system to evaluate the relative position of radioactive plaques secured beneath their intraocular tumors. This system consists of an automated, rotating, handheld, B-scan ultrasonographic probe operating at 10 MHz, a personal computer, and 3D imaging software.

RESULTS

We measured the margins of the plaque extending beyond the tumor and the distance between the radioactive seeds and the tumor apex. We also evaluated the relationship between the plaque edge, the episclera, and the tumor's edges. While the plaques were well centered over the tumor in all cases, the plaque margins around the tumor were found to be variably sized. When comparing measurements taken at the time of plaque insertion with those taken at the time of plaque removal, we noted changes in the apical tumor height and in plaque centration. In the 1 patient with a juxtapapillary tumor, the posterior margin of the plaque was found to be displaced away from the sclera, or "tilted."

CONCLUSIONS

Three-dimensional ultrasonography offers a new method for ophthalmic plaque localization. Unique perspectives can be visualized through the use of computer-aided 3D reconstructions that permit the assessment of the relative position of the plaque to the optic nerve and the measurement of the distance between the in vivo radioactive seed and the tumor apex. Our experience suggests that when compared with 2-dimensional ultrasonography, 3D ultrasonography offers new capabilities that can be used to improve plaque placement and radiation dose calculations.

Biosynthesis of proteoglycogen: modulation of glycogenin expression in the developing chicken

Glycogenin, the autoglucosyltransferase that primes the biosynthesis of proteoglycogen, is found in the polysaccharide linked proteoglycogen form in mammals and chicken. Glycogenin was released from proteoglycogen and its activity was measured, together with that of glycogen synthase as well as glycogen content, in muscle, liver, and brain during chicken development. The specific activity of glycogenin, expressed per protein, increased with development only in muscle and was higher than the specific activities measured in liver and brain at any time. Concomitant with the rise in activity, an enhanced expression of the protein was observed with Western blot. The specific activity of glycogen synthase increased with development in muscle and liver, while glycogen accumulation was noticeable only in liver. The results indicate that the molar concentration of proteoglycogen is higher in muscle than in liver. The high glycogen content of liver may indicate that the size of the polysaccharide moiety of proteoglycogen is larger in liver than in muscle. This is the first report of developmental modulation of de novo biosynthesis of glycogen at the level of the primer that initiates glucose polymerization.

[Nutritional status of preschool children in Ciudad de La Habana from 1972 to 1993]

Two anthropometric surveys of children and adolescents have been carried out in Cuba with national samples. A third study done in the province of Ciudad de la Habana provided information on the physical characteristics of the population in that area and a baseline for the periodic evaluation of its nutritional status. This article compares the weight and height results obtained in these surveys for children 0 to 5 years old who lived in this province with the international reference standards proposed by WHO. The results show that, despite the economic difficulties the country has faced, the prevalence of malnutrition is low. In 1993, the prevalence of low height-for-age was 3.1%; that of low weight-for-height, 0.4%; and that of low weight-for-age, 1.5%. Overweight was the most common type of malnutrition, with a prevalence of 5.2%. Between 1972 and 1993, the prevalence of chronic malnutrition fell 32.6%, acute malnutrition was reduced by 69.2%; malnutrition of all types decreased by 44.4%; and overweight fell 48.5%.

Allocation of biomass and mineral elements in Melilotus segetalis (annual sweetclover): effects of NaCl salinity and plant age

The allocation of biomass and mineral elements (Ka, K, Ca, P, N, Fe, Cu, Mn and Zn) during the ontogenetic cycle of annual sweetclover (Melilotus segetalis (Brot.) Ser.) growing under favourable and saline conditions has been studied. Plants were grown in a glasshouse, in pots with siliceous substrate and watered with Hoagland solution. Half were salinized by adding 170 mol m^-2 N₂ Cl (15 dS m^-1 ) to the solution. Eleven harvests at 15 d intervals measured the dry weight distribution within the plant and the mineral composition. Allocation relative to biomass (ARB) in each plant organ, both under favourable and salt-stress conditions, was calculated for each mineral element, Biomass and mineral elements were allocated independently within M. segetalis, and the general pattern thanked with age and was affected by salinity. Salt-stressed plants were smaller and invested proportionately more biomass in leaves. Na was accumulated in roots of young plants and excluded from leaves and fruits, whereas K was depleted from roots and accumulated in leaves and fruits. Immobile Ca accumulated in leaves, with age. Phloem-mobile P and X were translocated to flowers and fruits. Fe, Cu and Zn were diluted in leaves and not affected by salt; whereas Mn concentration increased with age and salinity. The switch to reproduction and increased demand for nutrients induced drastic changes in the allocation pattern of mineral elements. Salinity induced a re-allocation of biomass and mineral elements in all plant organs except the reproductive structures, as part of a whole-plant response to minimize salt toxic effects, to achieve osmotic adjustment, to preserve the reproductive output, and to compensate nutrient imbalance.

[Anomalies of the first branchial cleft]

Account of the case of a little girl of four and a half years brought to the consulting otologist because of her earache, otorrhoea, retroauricular inflammatory swelling and oedema of the external ear canal on left side. Frequency, evolution, diagnostic means and management measures for first branchial cleft are reviewed.

An investigation of injection techniques for local analgesia of the equine distal tarsus and proximal metatarsus

A positive radiographic contrast agent was injected into the tarsometatarsal (TMT) joints of both hindlimbs of 10 horses. Lateromedial radiographic views were obtained at 5, 15 and 30 mins after injection. Injection was successful in 19 of 20 limbs. Communication between the centrodistal (CD) and TMT joints was identified in 7 limbs (35%). Contrast agent extended around the tendons of tibialis cranialis (TC) and fibularis tertius (FT) in 18 limbs, and in 7 limbs some contrast entered the tarsal sheath. Slight to moderate plantar and/or distal extension of contrast agent was identified in 13 limbs. On a subsequent occasion positive contrast agent was injected subtarsally using one of two techniques and radiography was repeated. Contrast agent was principally distributed on the plantar aspect of the 3rd metatarsal bone, the plantar aspect of the suspensory ligament and between the superficial and deep digital flexor tendons. Extension of contrast agent into the TMT joint was identified in only 1 limb but in 8 limbs contrast agent extended into the tarsal sheath. The practical implications of these results include the possibility that local anaesthetic solution injected into the TMT joint may alleviate pain from the CD joint, the insertions of TC and FT or the tarsal sheath. It may also result in perineural analgesia of the dorsal metatarsal nerves or the plantar metatarsal nerves. In some cases subtarsal injection of local anaesthetic solution may result in alleviation of pain from the tarsal sheath. False negative results for subtarsal analgesia may be achieved by inadvertent injection into the tarsal sheath or into a blood or lymphatic vessel.

Uptake of lead and its influence in the alga Selenastrum capricornutum printz

The influence of nutrient level, hours of fight and the flux of air by volume of solution on uptake of lead has been examined from batch growth experiments carried out with the alga Selenastrum capricornutum Printz. The organic matter released by the alga has been characterized in terms of absorbance at 285 nm, dissolved organic carbon and maximum intensity of fluorescence at the excitation peak. The lability of lead complexes formed with the alga exudates has been investigated in terms of differential pulse anodic stripping voltammetry (DPASV). It has been noticed that lead inhibits the division of the cells which become bigger in size but with less pigment per cell.

floricaula: a homeotic gene required for flower development in antirrhinum majus

Plants carrying the floricaula (flo) mutation cannot make the transition from inflorescence to floral meristems and have indeterminate shoots in place of flowers. The flo-613 allele carries a Tam3 transposon insertion, which allowed the isolation of the flo locus. The flo gene encodes a putative protein (FLO) containing a proline-rich N-terminus and a highly acidic region. In situ hybridization shows that the flo gene is transiently expressed in the very early stages of flower development. The earliest expression seen is in bract primordia, followed by sepal, petal, and carpel primordia, but no expression is detected in stamen primordia. This pattern of expression has implications for how flo affects phyllotaxis, organ identity, and determinacy. We propose that flo interacts in a sequential manner with other homeotic genes affecting floral organ identity.

Changes in Net O(2) Exchange Induced by Inorganic Nitrogen in the Blue-Green Alga Anacystis nidulans

The response of net O(2) exchange to light intensity by intact Anacystis nidulans cells in the presence of saturating NaHCO(3) concentrations followed a curve with an inflection near the light-compensation point. Addition of either KNO(3) or NH(4)Cl stimulated O(2) uptake in the dark and at light intensities below the light-compensation point. This resulted in steeper slopes of the curve calculated below and above the light-compensation point. At O(2) concentrations limiting dark respiration, addition of inorganic nitrogen had no effect on either dark respiration or O(2) exchange in the light. The apparent changes in photosynthetic yield observed under normal O(2) concentration disappeared when respiration was limited by O(2) availability, indicating that the effects of inorganic nitrogen on O(2) exchange at low light intensities are due to stimulation of respiration rather than to increases in photosynthetic yield.

Determination of intracellular nitrate

A sensitive procedure has been developed for the determination of intracellular nitrate. The method includes: (i) preparation of cell lysates in 2 M-H3PO4 after separation of cells from the outer medium by rapid centrifugation through a layer of silicone oil, and (ii) subsequent nitrate analysis by ion-exchange h.p.l.c. with, as mobile phase, a solution containing 50 mM-H3PO4 and 2% (v/v) tetrahydrofuran, adjusted to pH 1.9 with NaOH. The determination of nitrate is subjected to interference by chloride and sulphate when present in the samples at high concentrations. Nitrite also interferes, but it is easily eliminated by treatment of the samples with sulphamic acid. The method has been successfully applied to the study of nitrate transport in the unicellular cyanobacterium Anacystis nidulans.

Relationship between a 47-kDa cytoplasmic membrane polypeptide and nitrate transport in Anacystis nidulans

The polypeptide composition of cytoplasmic membranes of the cyanobacterium Anacystis nidulans changes in response to variations in the nitrogen source available to the cells, differing specifically in the amount of a polypeptide of 47-kDa molecular mass. Synthesis of the polypeptide and expression of nitrate transport activity are repressed by ammonium. Transfer of ammonium-grown cells to a medium containing nitrate as the sole nitrogen source results in parallel development of the 47-kDa polypeptide and nitrate transport activity of the cells. These results suggest the involvement of the 47-kDa cytoplasmic membrane polypeptide in nitrate transport by A. nidulans.

Regulated nitrate transport in the cyanobacterium Anacystis nidulans

Intracellular accumulation of nitrate, indicative of the operation of an active nitrate transport system, has been measured in intact cells of the cyanobacterium Anacystis nidulans. The ability of the cells to accumulate nitrate was effectively hindered by either ammonium addition or selective inhibition of CO2 fixation by DL-glyceraldehyde, with the effect of either compound being prevented by previously blocking ammonium assimilation. The results support the contention that nitrate utilization in cyanobacteria is regulated at the level of nitrate transport through the concerted action of ammonium assimilation and CO2 fixation.