Comparing pulsed field electroporation and radiofrequency ablation for the treatment of paroxysmal atrial fibrillation: design and rationale of the BEAT PAROX-AF randomized clinical trial

AIMS

Using thermal-based energy sources [radiofrequency (RF) energy/cryo energy] for catheter ablation is considered effective and safe when performing pulmonary vein isolation (PVI) in patients with paroxysmal atrial fibrillation (AF). However, treatment success remains limited and complications can occur due to the propagation of thermal energy into non-target tissues. We aim to compare pulsed field ablation (PFA) with RF ablation in terms of efficacy and safety for patients with drug-resistant paroxysmal AF.

METHODS AND RESULTS

The BEAT PAROX-AF trial is a European multicentre, superiority, open-label randomized clinical trial in two parallel groups. A total of 292 participants were recruited in 9 high-volume European clinical centres in 5 countries. Patients with paroxysmal AF were randomized to PFA (FARAPULSE Endocardial Ablation System©, Boston Scientific) or RF using the CLOSE protocol with contact force sensing catheter (SmartTouch© catheter and CARTO© Biosense Webster). The primary endpoint will be the 1-year recurrence of atrial arrhythmia, and the major secondary safety endpoint will be the occurrence of acute (<7 days) procedure-related serious adverse events, or pulmonary vein stenosis, or atrio-oesophageal fistula up to 12 months. Additionally, five sub-studies investigate the effect of PFA on oesophageal safety, cerebral lesions, cardiac autonomic nervous system, durability of PVI as assessed during redo ablation procedures, and atrial and ventricular function. The study began on 27 December 2021 and concluded recruitment on 17 January 2024. Results will be available in mid-2025.

CONCLUSION

The BEAT PAROX-AF trial aims to provide critical insights into the optimal treatment approach for patients with paroxysmal AF.

Durability of Pulmonary Vein Isolation Using Pulsed-Field Ablation: Results From the Multicenter EU-PORIA Registry

BACKGROUND

Pulsed-field ablation (PFA) is a novel nonthermal ablation technology with high procedural safety and efficiency for pulmonary vein isolation (PVI). Premarket data showed high PVI durability during mandatory remapping studies. Data on lesion durability in real-world patients with clinically indicated redo procedures are scarce.

OBJECTIVES

This study sought to report PVI durability rates in patients undergoing a clinically indicated redo procedure after an index PVI using PFA.

METHODS

Patients from 7 European centers undergoing an index PVI using PFA were included the EU-PORIA (European Real-world Outcomes With Pulsed Field Ablation in Patients With Symptomatic Atrial Fibrillation) registry. In patients with subsequent left atrial redo procedures due to arrhythmia recurrence, 3-dimensional electroanatomical maps were acquired. PVI durability was assessed on a per-vein and per-patient level, and sites of reconnections and predictors of lesion durability were identified.

RESULTS

Of 1,184 patients (62% paroxysmal atrial fibrillation) undergoing an index PVI using PFA, 272 (23%) had an arrhythmia recurrence. Of these, 144 (53%) underwent a left atrial redo procedure a median of 7 (Q1-Q3: 5-10) months after the first ablation. Three-dimensional electroanatomical maps identified 404 of 567 pulmonary veins (71%) with durable isolation. In 54 patients (38%), all pulmonary veins were durably isolated. Prior operator experience with cryoballoon ablation was associated with a higher PVI durability compared to operators with only point-by-point radiofrequency experience (76% vs 60%; P < 0.001). Neither the operators' cumulative experience in atrial fibrillation ablation (≤5 vs >5 years) nor the size of the PFA device used (31 mm vs 35 mm) had an impact on subsequent lesion durability (both P > 0.50).

CONCLUSIONS

In 144 patients with arrhythmia recurrence after PFA PVI, durable isolation was observed in 71% of the pulmonary veins during the redo procedure, and 38% of all patients showed durable isolation of all veins.

Pulmonary vein narrowing after pulsed field versus thermal ablation

AIMS

When it occurs, pulmonary vein (PV) stenosis after atrial fibrillation (AF) ablation is associated with significant morbidity. Even mild-to-moderate PV narrowing may have long-term implications. Unlike thermal ablation energies, such as radiofrequency (RF) or cryothermy, pulsed field ablation (PFA) is a non-thermal modality associated with less fibrotic proliferation. Herein, we compared the effects of PFA vs. thermal ablation on PV narrowing after AF ablation.

METHODS AND RESULTS

ADVENT was a multi-centre, randomized, single-blind study comparing PFA (pentaspline catheter) with thermal ablation-force-sensing RF or cryoballoon (CB)-to treat drug-refractory paroxysmal AF. Pulmonary vein diameter and aggregate cross-sectional area were obtained by baseline and 3-month imaging. The pre-specified, formally tested, secondary safety endpoint compared a measure of PV narrowing between PFA vs. thermal groups, with superiority defined by posterior probability > 0.975. Among subjects randomized to PFA (n = 305) or thermal ablation (n = 302), 259 PFA and 255 thermal ablation (137 RF and 118 CB) subjects had complete baseline and 3-month PV imaging. No subject had significant (≥70%) PV stenosis. Change in aggregate PV cross-sectional area was less with PFA (-0.9%) than thermal ablation (-12%, posterior probability > 0.999)-primarily driven by the RF sub-cohort (-19.5%) vs. CB sub-cohort (-3.3%). Almost half of all PFA PV diameters did not decrease, but the majority (80%) of RF PVs decreased, regardless of PV anatomic location.

CONCLUSION

In this first randomized comparison of PFA vs. thermal ablation, PFA resulted in less PV narrowing-thereby underscoring the qualitatively differential and favourable impact of PFA on PV tissue.

Pulsed Field or Conventional Thermal Ablation for Paroxysmal Atrial Fibrillation

BACKGROUND

Catheter-based pulmonary vein isolation is an effective treatment for paroxysmal atrial fibrillation. Pulsed field ablation, which delivers microsecond high-voltage electrical fields, may limit damage to tissues outside the myocardium. The efficacy and safety of pulsed field ablation as compared with conventional thermal ablation are not known.

METHODS

In this randomized, single-blind, noninferiority trial, we assigned patients with drug-refractory paroxysmal atrial fibrillation in a 1:1 ratio to undergo pulsed field ablation or conventional radiofrequency or cryoballoon ablation. The primary efficacy end point was freedom from a composite of initial procedural failure, documented atrial tachyarrhythmia after a 3-month blanking period, antiarrhythmic drug use, cardioversion, or repeat ablation. The primary safety end point included acute and chronic device- and procedure-related serious adverse events.

RESULTS

A total of 305 patients were assigned to undergo pulsed field ablation, and 302 were assigned to undergo thermal ablation. At 1 year, the primary efficacy end point was met (i.e., no events occurred) in 204 patients (estimated probability, 73.3%) who underwent pulsed field ablation and 194 patients (estimated probability, 71.3%) who underwent thermal ablation (between-group difference, 2.0 percentage points; 95% Bayesian credible interval, -5.2 to 9.2; posterior probability of noninferiority, >0.999). Primary safety end-point events occurred in 6 patients (estimated incidence, 2.1%) who underwent pulsed field ablation and 4 patients (estimated incidence, 1.5%) who underwent thermal ablation (between-group difference, 0.6 percentage points; 95% Bayesian credible interval, -1.5 to 2.8; posterior probability of noninferiority, >0.999).

CONCLUSIONS

Among patients with paroxysmal atrial fibrillation receiving a catheter-based therapy, pulsed field ablation was noninferior to conventional thermal ablation with respect to freedom from a composite of initial procedural failure, documented atrial tachyarrhythmia after a 3-month blanking period, antiarrhythmic drug use, cardioversion, or repeat ablation and with respect to device- and procedure-related serious adverse events at 1 year. (Funded by Farapulse-Boston Scientific; ADVENT ClinicalTrials.gov number, NCT04612244.).

EUropean real-world outcomes with Pulsed field ablatiOn in patients with symptomatic atRIAl fibrillation: lessons from the multi-centre EU-PORIA registry

AIMS

Pulsed field ablation (PFA) is a new, non-thermal ablation modality for pulmonary vein (PV) isolation in patients with atrial fibrillation (AF). The multi-centre EUropean Real World Outcomes with Pulsed Field AblatiOn in Patients with Symptomatic AtRIAl Fibrillation (EU-PORIA) registry sought to determine the safety, efficacy, and learning curve characteristics for the pentaspline, multi-electrode PFA catheter.

METHODS AND RESULTS

All-comer AF patients from seven high-volume centres were consecutively enrolled. Procedural and follow-up data were collected. Learning curve effects were analysed by operator ablation experience and primary ablation modality. In total, 1233 patients (61% male, mean age 66 ± 11years, 60% paroxysmal AF) were treated by 42 operators. In 169 patients (14%), additional lesions outside the PVs were performed, most commonly at the posterior wall (n = 127). Median procedure and fluoroscopy times were 58 (interquartile range: 40-87) and 14 (9-21) min, respectively, with no differences due to operator experience. Major complications occurred in 21/1233 procedures (1.7%) including pericardial tamponade (14; 1.1%) and transient ischaemic attack or stroke (n = 7; 0.6%), of which one was fatal. Prior cryoballoon users had less complication. At a median follow-up of 365 (323-386) days, the Kaplan-Meier estimate of arrhythmia-free survival was 74% (80% for paroxysmal and 66% for persistent AF). Freedom from arrhythmia was not influenced by operator experience. In 149 (12%) patients, a repeat procedure was performed due to AF recurrence and 418/584 (72%) PVs were durably isolated.

CONCLUSION

The EU-PORIA registry demonstrates a high single-procedure success rate with an excellent safety profile and short procedure times in a real-world, all-comer AF patient population.

Electrophysiology, Pathology, and Imaging of Pulsed Field Ablation of Scarred and Healthy Ventricles in Swine

BACKGROUND

Pulsed field ablation (PFA) has recently been shown to penetrate ischemic scar, but details on its efficacy, risk of arrhythmias, and imaging insights are lacking. In a porcine model of myocardial scar, we studied the ability of ventricular PFA to penetrate scarred tissue, induce ventricular arrhythmias, and assess the influence of QRS gating during pulse delivery.

METHODS

Of a total of 6 swine, 5 underwent coronary occlusion and 1 underwent radiofrequency ablation to create infarct scar and iatrogenic scar models, respectively. Two additional swine served as healthy controls. An 8 Fr focal PFA catheter was used to deliver bipolar, biphasic PFA (2.0 kV) lesions guided by electroanatomical mapping, fluoroscopy, and intracardiac echocardiography over both scarred and healthy myocardium. Swine underwent magnetic resonance imaging 2-7 days post-PFA.

RESULTS

PFA successfully penetrated scar without significant difference in lesion depth between lesion at the infarct border (5.9±1.0 mm, n=41) and healthy myocardium (5.7±1.3 mm, n=26; P=0.53). PFA penetration of both infarct and iatrogenic radiofrequency abalation scar was observed in all examined sections. Sustained ventricular arrhythmias requiring defibrillation occurred in 4 of 187 (2.1%) ungated applications, whereas no ventricular arrhythmias occurred during gated PFA applications (0 of 64 [0%]). Dark-blood late-gadolinium-enhanced sequences allowed for improved endocardial border detection as well as lesion boundaries compared with conventional bright-blood late-gadolinium-enhanced sequences.

CONCLUSIONS

PFA penetrates infarct and iatrogenic scar successfully to create deep lesions. Gated delivery eliminates the occurrence of ventricular arrhythmias observed with ungated porcine PFA. Optimized magnetic resonance imaging sequences can be helpful in detecting lesion boundaries.

Effect of Epicardial Pulsed Field Ablation Directly on Coronary Arteries

BACKGROUND

The unique tissue selectivity of pulsed field ablation (PFA) allows for minimizing collateral damage to the nerves/esophagus. However, the safety profile of epicardial PFA on coronary arteries (CAs) has not been well defined.

OBJECTIVES

This study sought to evaluate the effect of epicardial PFA directly on CAs in a swine model.

METHODS

In 4 swine, an 8-F linear quadripolar PFA catheter (FARAPULSE Inc) was introduced into the pericardial space via a subxiphoid puncture. After coronary angiography (Angio), QRS synchronized, biphasic, bipolar PFA was delivered directly on the left anterior descending artery, left circumflex artery, or normal myocardium (control) (2.0 kV × 4 applications per site). Angio was repeated immediately after ablation and repeated every 5 minutes to quantify the degree of CA narrowing. After 4- or 8-week survival, repeat Angio was performed followed by gross and histologic lesion analyses.

RESULTS

A total of 15 lesions were delivered (8 left anterior descending arteries, 3 left circumflexes, and 4 controls). Target site Angio revealed median of 47% (IQR: 38%-69%) acute luminal narrowing immediately after PFA, which gradually resolved over 30 minutes. Epicardial PFA lesions extended into the myocardium with a median depth of 4.1 mm (IQR: 3.6-5.6 mm) passing across the CAs and adipose tissue. However, 87.5% of the CAs demonstrated minimal to mild CA stenosis associated with neointimal hyperplasia and tunica media fibrosis.

CONCLUSIONS

In a swine model, epicardial PFA directly on CAs allowed the creation of myocardial lesions but led to a CA response characterized by acute moderate spasm and chronic mild stenosis via neointimal hyperplasia.

An objective method to evaluate radiation dose distributions varying by three orders of magnitude

PURPOSE

Modern radiotherapy practices typically report the absorbed dose (D) within the 5% relative isodose volume (i.e., the therapeutic dose region) to an accuracy of 3%-5%. Gamma-index analysis, the most commonly used method to evaluate dosimetric accuracy, has low sensitivity to discrepancies that occur outside of this region. The objective of this study was to develop an evaluation method with high sensitivity across dose distributions spanning three orders of magnitude.

METHODS

We generalized the gamma index to include an additional criterion, the absolute absorbed dose difference, specifically for the low-dose region (i.e., D ≤ 5%). We also proposed a method to objectively select the appropriate magnitudes for relative-dose-difference, absolute-dose-difference, and distance-to-agreement criteria. We demonstrated the generalized gamma-index method by first finding the appropriate generalized gamma-index agreement criteria at an interval of specified passing rates. Next, we used the generalized gamma index to evaluate one-, two-, and three-dimensional absorbed dose distributions in a water-box phantom and voxelized patient geometry.

RESULTS

Generalized gamma-index passing rates for one-, two-, and three-dimensional dose distributions were 55.4%, 44.5%, and 8.9%, respectively. Traditional gamma-index passing rates were 100%, 97.8%, and 96.4%, respectively. These results reveal that the generalized method has adequate sensitivity in all regions (i.e., therapeutic and low dose). Additionally, the algorithmic determination of triplets of agreement criteria revealed that they are strong functions of the specified passing rate.

CONCLUSIONS

The major finding of this work is that the proposed method provides an objective evaluation of the agreement of dose distributions spanning three orders of magnitude. In particular, this generalized method correctly characterized dosimetric agreement in the low-dose region, which was not possible by traditional methods. The proposed algorithmic selection of agreement criteria decreased subjectivity and requirements of user judgment and skill. This method could find utility in a variety of applications including dose-algorithm development and translation.

A descriptive and broadly applicable model of therapeutic and stray absorbed dose from 6 to 25 MV photon beams

PURPOSE

To develop a simple model of therapeutic and stray absorbed dose for a variety of treatment machines and techniques without relying on proprietary machine-specific parameters.

METHODS

Dosimetry measurements conducted in this study and from the literature were used to develop an analytical model of absorbed dose from a variety of treatment machines and techniques in the 6 to 25 MV interval. A modified one-dimensional gamma-index analysis was performed to evaluate dosimetric accuracy of the model on an independent dataset consisting of measured dose profiles from seven treatment units spanning four manufacturers.

RESULTS

The average difference between the calculated and measured absorbed dose values was 9.9% for those datasets on which the model was trained. Additionally, these results indicate that the model can provide accurate calculations of both therapeutic and stray radiation dose from a wide variety of radiotherapy units and techniques.

CONCLUSIONS

We have developed a simple analytical model of absorbed dose from external beam radiotherapy treatments in the 6 to 25 MV beam energy range. The model has been tested on measured data from multiple treatment machines and techniques, and is broadly applicable to contemporary external beam radiation therapy.

Crystallization of zirconia based thin films

The crystallization kinetics of amorphous 3 and 8 mol% yttria stabilized zirconia (3YSZ and 8YSZ) thin films grown by pulsed laser deposition (PLD), spray pyrolysis and dc-magnetron sputtering are explored. The deposited films were heat treated up to 1000 °C ex situ and in situ in an X-ray diffractometer. A minimum temperature of 275 °C was determined at which as-deposited amorphous PLD grown 3YSZ films fully crystallize within five hours. Above 325 °C these films transform nearly instantaneously with a high degree of micro-strain when crystallized below 500 °C. In these films the t'' phase crystallizes which transforms at T > 600 °C to the t' phase upon relaxation of the micro-strain. Furthermore, the crystallization of 8YSZ thin films grown by PLD, spray pyrolysis and dc-sputtering are characterized by in situ XRD measurements. At a constant heating rate of 2.4 K min(-1) crystallization is accomplished after reaching 800 °C, while PLD grown thin films were completely crystallized already at ca. 300 °C.

Multiferroic properties of o-LuMnO3 controlled by b-axis strain

Strain is a leading candidate for controlling magnetoelectric coupling in multiferroics. Here, we use x-ray diffraction to study the coupling between magnetic order and structural distortion in epitaxial films of the orthorhombic (o-) perovskite LuMnO(3). An antiferromagnetic spin canting in the E-type magnetic structure is shown to be related to the ferroelectrically induced structural distortion and to a change in the magnetic propagation vector. By comparing films of different orientations and thicknesses, these quantities are found to be controlled by b-axis strain. It is shown that compressive strain destabilizes the commensurate E-type structure and reduces its accompanying ferroelectric distortion.

Nearly amorphous Mo-N gratings for ultimate resolution in extreme ultraviolet interference lithography

We present fabrication and characterization of high-resolution and nearly amorphous Mo1 - xNx transmission gratings and their use as masks for extreme ultraviolet (EUV) interference lithography. During sputter deposition of Mo, nitrogen is incorporated into the film by addition of N2 to the Ar sputter gas, leading to suppression of Mo grain growth and resulting in smooth and homogeneous thin films with a negligible grain size. The obtained Mo0.8N0.2 thin films, as determined by x-ray photoelectron spectroscopy, are characterized to be nearly amorphous using x-ray diffraction. We demonstrate a greatly reduced Mo0.8N0.2 grating line edge roughness compared with pure Mo grating structures after e-beam lithography and plasma dry etching. The amorphous Mo0.8N0.2 thin films retain, to a large extent, the benefits of Mo as a phase grating material for EUV wavelengths, providing great advantages for fabrication of highly efficient diffraction gratings with extremely low roughness. Using these grating masks, well-resolved dense lines down to 8 nm half-pitch are fabricated with EUV interference lithography.

Strain-induced ferromagnetism in antiferromagnetic LuMnO3 thin films

Single phase and strained LuMnO(3) thin films are discovered to display coexisting ferromagnetic and antiferromagnetic orders. A large moment ferromagnetism (≈1μ(B)), which is absent in bulk samples, is shown to display a magnetic moment distribution that is peaked at the highly strained substrate-film interface. We further show that the strain-induced ferromagnetism and the antiferromagnetic order are coupled via an exchange field, therefore demonstrating strained rare-earth manganite thin films as promising candidate systems for new multifunctional devices.

Electric-field-induced polar order and localization of the confined electrons in LaAlO3/SrTiO3 heterostructures

With ellipsometry, x-ray diffraction, and resistance measurements we investigated the electric-field effect on the confined electrons at the LaAlO3/SrTiO3 interface. We obtained evidence that the localization of the electrons at negative gate voltage is induced, or at least enhanced, by a polar phase transition in SrTiO3 which strongly reduces the lattice polarizability and the subsequent screening. In particular, we show that the charge localization and the polar order of SrTiO3 both develop below ∼50  K and exhibit similar, unipolar hysteresis loops as a function of the gate voltage.

Evolution of the interfacial structure of LaAlO3 on SrTiO3

The evolution of the atomic structure of LaAlO_{3} grown on SrTiO_{3} was investigated using surface x-ray diffraction in conjunction with model-independent, phase-retrieval algorithms between two and five monolayers film thickness. A depolarizing buckling is observed between cation and oxygen positions in response to the electric field of polar LaAlO_{3}, which decreases with increasing film thickness. We explain this in terms of competition between elastic strain energy, electrostatic energy, and electronic reconstructions. Based on these structures, the threshold for formation of a two-dimensional electron system at a film thickness of 4 monolayers is quantitatively explained. The findings are also qualitatively reproduced by density-functional-theory calculations.

Dynamical response and confinement of the electrons at the LaAlO3/SrTiO3 interface

With infrared ellipsometry and transport measurements we investigated the electrons at the interface between LaAlO3 and SrTiO3. We obtained a sheet carrier concentration of N(s) approximately = 5-9x10(13) cm(-2), an effective mass of m*=3.2+/-0.4m(e), and a strongly frequency dependent mobility. The latter are similar as in bulk SrTi(1-x)Nb(x)O3 and therefore suggestive of polaronic correlations. We also determined the vertical concentration profile which has a strongly asymmetric shape with a rapid initial decay over the first 2 nm and a pronounced tail that extends to about 11 nm.

Profiling the interface electron gas of LaAlO3/SrTiO3 heterostructures with hard x-ray photoelectron spectroscopy

The conducting interface of LaAlO3/SrTiO3 heterostructures has been studied by hard x-ray photoelectron spectroscopy. From the Ti 2p signal and its angle dependence we derive that the thickness of the electron gas is much smaller than the probing depth of 4 nm and that the carrier densities vary with increasing number of LaAlO3 overlayers. Our results point to an electronic reconstruction in the LaAlO3 overlayer as the driving mechanism for the conducting interface and corroborate the recent interpretation of the superconducting ground state as being of the Berezinskii-Kosterlitz-Thouless type.

Electron scattering at dislocations in LaAlO3/SrTiO3 interfaces

We report experimental investigations of the effects of microstructural defects and of disorder on the properties of 2D electron gases at oxide interfaces. The cross section for scattering of electrons at dislocations in LaAlO(3)/SrTiO(3) interfaces has been measured and found to equal approximately 5 nm. Our experiments reveal that the transport properties of these electron gases are strongly influenced by scattering at dislocation cores.

Maintenance of geometric alterations associated with percutaneous mitral valve repair: real-time three-dimensional echocardiographic assessment in an ovine model

BACKGROUND AND AIM OF THE STUDY

Percutaneous catheter-based mitral annuloplasty (PTMA) exploits the anatomic proximity of the coronary sinus (CS) to the mitral valve apparatus. Acute results of PTMA have been favorable, but the durability of the geometric alterations associated with PTMA has not been reported. The study aim was to assess the three-dimensional (3D) geometry of the mitral annulus (MA) in normal sheep at 20 weeks after PTMA implantation.

METHODS

A PTMA device was implanted percutaneously in the CS of 10 normal sheep without mitral regurgitation. All animals were followed for 20 weeks with real-time 3D echocardiography (RT3DE). The MA area, the diagonal diameters in four directions, and the angle alpha, representing the degree of the saddle shape of MA, were determined.

RESULTS

No significant hemodynamic, pathologic or mechanical complications were observed during implantation or follow up. Both, the MA area (from 4.8 +/- 0.9 cm2 to 3.7 +/- 0.9 cm2) and anterior-posterior (A-P) diameter (from 21.4 +/- 3.0 mm to 17.6 +/- 2.4 mm) were reduced immediately after the procedure (both p <0.05). The angle alpha decreased after the procedure (from 142.0 +/- 11.5 degrees to 128.3 +/- 15.6 degrees; p <0.05). These changes remained stable over the 20-week follow up period.

CONCLUSION

RT3DE demonstrates that PTMA reduces the MA area and A-P diameter and maintains the physiologic curved or saddle shape of the MA. These changes remained stable for 20 weeks after device implantation.

Nanoscale control of an interfacial metal-insulator transition at room temperature

Experimental and theoretical investigations have demonstrated that a quasi-two-dimensional electron gas (q-2DEG) can form at the interface between two insulators: non-polar SrTiO3 and polar LaTiO3 (ref. 2), LaAlO3 (refs 3-5), KTaO3 (ref. 7) or LaVO3 (ref. 6). Electronically, the situation is analogous to the q-2DEGs formed in semiconductor heterostructures by modulation doping. LaAlO3/SrTiO3 heterostructures have recently been shown to exhibit a hysteretic electric-field-induced metal-insulator quantum phase transition for LaAlO3 thicknesses of 3 unit cells. Here, we report the creation and erasure of nanoscale conducting regions at the interface between two insulating oxides, LaAlO3 and SrTiO3. Using voltages applied by a conducting atomic force microscope (AFM) probe, the buried LaAlO3/SrTiO3 interface is locally and reversibly switched between insulating and conducting states. Persistent field effects are observed using the AFM probe as a gate. Patterning of conducting lines with widths of approximately 3 nm, as well as arrays of conducting islands with densities >10(14) inch(-2), is demonstrated. The patterned structures are stable for >24 h at room temperature.

Superconducting Interfaces Between Insulating Oxides

At interfaces between complex oxides, electronic systems with unusual electronic properties can be generated. We report on superconductivity in the electron gas formed at the interface between two insulating dielectric perovskite oxides, LaAlO3 and SrTiO3. The behavior of the electron gas is that of a two-dimensional superconductor, confined to a thin sheet at the interface. The superconducting transition temperature of congruent with 200 millikelvin provides a strict upper limit to the thickness of the superconducting layer of congruent with 10 nanometers.

Tunable Quasi-Two-Dimensional Electron Gases in Oxide Heterostructures

We report on a large electric-field response of quasi-two-dimensional electron gases generated at interfaces in epitaxial heterostructures grown from insulating oxides. These device structures are characterized by doping layers that are spatially separated from high-mobility quasi-two-dimensional electron gases and therefore present an oxide analog to semiconducting high-electron mobility transistors. By applying a gate voltage, the conductivity of the electron gases can be modulated through a quantum phase transition from an insulating to a metallic state.

Electron transport through YBa2Cu3O7-delta grain boundary interfaces between 4.2 and 300 K

The current-induced dissipation in YBa(2)Cu(3)O(7-delta) grain boundary tunnel junctions has been measured between 4.2 and 300 K. It is found that the resistance of 45 degrees (100)/(110) junctions decreases linearly by a factor of 4 when their temperature is increased from 100 to 300 K. At the superconducting transition temperature T(c) the grain boundary resistance of the normal state and of the superconducting state extrapolates to the same value.

d-wave induced zero-field resonances in dc pi-superconducting quantum interference devices

A dc pi SQUID consists of a superconducting ring interrupted by two Josephson junctions, one of which carries in equilibrium a pi phase difference, caused, for example, by the d-wave pairing symmetry of the high- T(c) cuprates. If this phase shift is maintained in the voltage state, anomalous resonance currents are expected in the SQUIDs transport characteristics. Here we report the observation of such resonances for high- T(c) dc pi SQUIDs, providing evidence for the influence of the d-wave symmetry on the voltage state of a Josephson junction for frequencies of several tens of GHz.

Evidence of doping-dependent pairing symmetry in cuprate superconductors

Scanning tunneling spectroscopy studies reveal long-range spatial homogeneity and predominantly d(x(2)-y(2))-pairing spectral characteristics in under- and optimally doped YBa2Cu 3O (7-delta) superconductors, whereas STS on YBa2(Cu 0.9934Zn 0.0026Mg (0.004))3O (6.9) exhibits microscopic spatial modulations and strong scattering near the Zn or Mg impurity sites, together with global suppression of the pairing potential. In contrast, in overdoped (Y 0.7Ca (0.3))Ba 2Cu 3O (7-delta), (d(x(2)-y(2))+s)-pairing symmetry is found, suggesting significant changes in the superconducting ground state at a critical doping value.

Phototaxic behavior and the retinotectal transport of horseradish peroxidase (HRP) in surgically created cyclopean salamander larvae (Ambystoma)

Negative phototaxis (NP) was used to evaluate the recovery of vision in albino axolotl larvae with one eye discarded and the other transplanted either to the orbit (orthoclops) or to the top of the head (cyclops). NP was assessed at approximately 1, 2 and 3 months postoperatively, using an automated, infrared monitor. Some 88% of the orthoclopes and 64% of the cyclopes recovered NP. However, among the cyclopes that did recover, the quantitative aspects of NP were virtually the same as those of the orthoclopes. That the cyclopean eye can regenerate retinotectal pathways was established by anterograde tracing of horseradish peroxidase (HRP). But where previously uninjured animals transported HRP to the contralateral tectum, both the cyclopes and the orthoclopes distributed the enzyme to the left and right tectal halves. Heavy deposits of HRP were found in the tecta of some animals that lacked NP. To find out if an optic tectum is actually required for NP, a series of ablation experiments were performed, using Ambystoma punctatum larvae. Tectectomy had the same effect on NP as bilaterally extirpating the eyes or intracranially severing both optic nerves, i.e. removing the tectum abolished NP.

THE RESULTS

(1) confirm the efficacy of the ectopic eye in the cyclops preparation; (2) show that the ectopic eye can regenerate retinotectal pathways; (3) indicate that retinotectal contact is a necessary but insufficient condition for NP.

Measures of phototaxis and movement detection in the larval salamander

In this investigation, we describe two precise tests of visual function that integrate quasinatural situations with time-lapse video recording and infrared computerized monitoring of activity to assess movement detection and phototaxic tendencies, respectively. Four groups of larvae from A. punctatum, A. tigrinum, A. mexicanum, and a mutant albino axolotl were tested in an alley containing light and dark halves and lined with infrared sensors to monitor their phototaxic response. A. punctatum showed no phototaxic tendency, while the other three groups displayed a strong negative phototaxic response. Enucleation of the eyes in mutant albinos eliminated the negative phototaxis. Visual detection of motion was tested by videorecording the behavior of A. punctatum, A. mexicanum, and the mutant albino axolotl larvae while they explored a large bowl with 6 small vials on the perimeter, one of which contained white worms. A. punctatum rapidly approached the worm vial and engaged in intense predatory behavior. A. mexicanum responded to the presence of worms very slowly and rapidly lost interest. Albino axolotls displayed no visual recognition of the worms. The results indicate that visual function can be precisely determined in larval salamanders utilizing behavioral measures consistent with the animal's natural tendencies.

Tectectomy in the cyclopean salamander

In an Ambystoma larva with both natural eyes removed and one eye grafted atop the head (Cyclops preparation), vision-dependent behavior usually recovers from the enucleation inherent in the operation, but the optically activated skin blanching reaction reappears in a very small number of instances. In the present studies, while the latter trend continued for the conventional Cyclops preparation, tectectomy concurrent with the ectopic eye transplantation resulted in a several-fold increase in the recovery of blanching competency. Some 60 percent of the tectectomized Cyclops animals exhibited the same Hogben-Slome pigmentation indices as larvae with one natural eye intact (controls). As measured planimetrically with an image analyzer, the pigment spots (melanosome containing portions of dermal melanocytes) contracted to the same extent in the blanch-competent Cyclops animals as in controls with a single natural eye.

Anterior decerebration blocks visual habituation in the larval salamander (Ambystoma punctatum)

Amputation of the rostral half of the cerebrum induces a compulsion-like reaction in larval Ambystoma punctatum towards Enchytraeus protected within glass vials. Normal and craniotomized larvae are visually attracted to worm-containing vials, as revealed by time-lapse video taping but, after several unsuccessful attempts to get the prey, habituate and depart. The video tapes revealed that anteriorly decerebrated animals spent as much as 100 of 120 minutes at the worm-containing vial, repeatedly but futilely attacking the glass. The data indicate that the telencephalon plays an active negative role in the salamander larva's visually guided behavior.

Two-eyed versus one-eyed salamanders: does binocularity enhance the optically evoked skin blanching reactions of Ambystoma larvae?

A wide variety of visual functions show increases attributable to binocularity, and the question pursued here was whether a second eye enhances the visually stimulated skin blanching reaction of the larval salamander. Dermal melanin spots (produced by the aggregations of melanosomes within dermal melanophores and which contract or expand to lighten or darken the skin) were measured in eyeless (controls), one-eyed and two-eyed Ambystoma punctatum larvae after chronic adaptation of the subjects to a white background (i.e., stimulus conditions for maximum blanching). The eyeless subjects showed no blanching (thus remained dark) in white cups, and they exhibited melanin spots 7 or 8 times the size of those of the other two groups. All one-eyed or two-eyed subjects exhibited blanching reactions; planometric comparison revealed a significantly larger melanin spot area for one-eyed than for two-eyed animals; i.e., the binocular condition permitted greater contraction of the pigment spots than did the monocular condition. Analytical data compared favorably with independently ascertained pigmentation indices. The results indicate that a second eye quantitatively elevates the blanching maximum of a larval salamander.

Carbon dioxide absorption of He-Ne laser radiation at 4.2 microm: characteristics of self and nitrogen broadened cases

A laser resonance absorption spectrometer is used to investigate the characteristics of both self and nitrogen collision broadened carbon dioxide in resonance with He-Ne laser radiation at 4.2 microm. The absorption coefficient in these broadening conditions has contributions from the R(28) to R(34) absorption lines of the nu(3) CO(2) spectrum. The Fletcher-Powell optimization method is used to reduce the raw absorption data and to find the best value average collision broadening coefficient and laser emission frequency for a Lorentzian line shape model of the contributing lines. Pure carbon dioxide absorption in a pressure range of from 0.0016 atm (1.25 Torr) to 0.33 atm (250 Torr) is described well by the model with an average self broadening coefficient of 0.084 +/- 0.008 cm(-1) atm(-1) for laser frequencies located at either 2370.591 +/- 0.020 cm(-1) or 2371.135 +/- 0.019 cm(-1). Nitrogen broadened carbon dioxide in the total pressure range of from 0.13 atm (100 Torr) to 1.18 atm (900 Torr) is characterized by the same model with the laser frequency at 2371.102 +/- 0.007 cm(-1) atm(-1). The average absorption coefficient for low concentrations of carbon dioxide in a 1-atm total pressure nitrogen environment has been determined experimentally as 9.90 +/- 1.49 cm(-1) atm(-1). All the listed results are at 296 K.

Transplanted eyes of foreign donors can reinstate the optically activated skin camouflage reactions in bilaterally enucleated salamanders (Ambystoma)

Bilateral enucleation immediately and irreversibly cancels the skin camouflage reactions of Ambystoma larvae. A heteroplastic eye transplant can reinstate the latter reaction. Recipients of a heteroplastic eye recovered the reaction as frequently and to the same extent as animals with one of their own eyes reattached.

The ethanol sensitivity of calcium taken up by a depolarization-dependent process in mouse strains DBA and C57BL

In vitro effects of ethanol on calcium taken up by synaptosomes were examined in two strains of mice, C57BL and DBA, that exhibit marked differences in alcohol sensitivity and preference. There were no significant strain differences in basal or depolarization-dependent synaptosomal calcium levels. Ethanol did not reduce the basal calcium level but instead reduced depolarization-dependent calcium levels with the same potency in both strains. These results do not support a role for changes of calcium levels as the basis for differences in ethanol sensitivity in these mouse strains.

Vision and the skin camouflage reactions of Ambystoma larvae: the effects of eye transplants and brain lesions

Salamander larvae typically adapt their dermal melanophores to achieve camouflage, and it has been known for some time that removal of the eyes abolishes the response. Here we survey the contribution of the optic system to the bright and dark camouflage reactions and report that: the stimulus depends on an interaction between the direct and reflected light; an eye mounted atop the head and oriented vertically tended not to support camouflage, even though the animal responded to visual cues and learned a vision-dependent task; deviating the transplanted eye off the vertical axis enhanced the recovery of camouflage reactions; amputating or reorienting the telencephalon, epithalamus, pretectum or tectum did not abolish either camouflage reaction whereas lesions of the ventral optic pathway blocked brightening; transection near the midbrain-hindbrain junction--well posterior to known optic terminals--retarded the dark reaction; when the latter lesion was combined with disconnection of the telencephalon and epithalamus, contrary to predictions from the lesions executed separately, the animals lost the bright reaction; the hypophysis is necessary for darkening, but the organ supported this reaction even though detached, displaced or reoriented; and the pineal body was not essential for the grosser aspects of camouflage in Ambystoma larvae but may play an adjunctive role in fine tuning.

Age differences in the oxidation of and neural response to ethanol in mice

Male mice (C57BL/6J) from three age groups, 4, 14, and 26 months, were tested to determine their oxidation rate of intragastrically infused ethanol and the response of the centrally mediated jaw-jerk reflex to ethanol challenge. There were no age-related differences in the rate of oxidation of ethanol. However, age differences in ethanol-induced decrement of the jaw-jerk amplitude were significant. The 26 month animals were the most affected, followed by the 4 month group. The middle aged mice (14 month) showed the greatest resistance to the depression induced by ethanol. The results were evaluated with regard to the current hypotheses.

Oxidation of alcohol in free-moving mice from high and low preference strains

Free-moving mice from the high-alcohol preference C57BL/6J strain and low-preference DBA/2J strain were slowly fed [2-14C]ethanol intragastrically until anesthesia was achieved. Behavior was monitored in a Plexiglas metabolic chamber while 14CO2 was simultaneously trapped to determine the rate of ethanol metabolism. Average time to the loss of the righting reflex in the DBA/2J was 21.9 min and 27.9 min for the C57BL/6J strain (p less than 0.005). Elimination of 14CO2 was slightly higher (n.s.) in the DBA/2J strain for the entire monitoring period. Infusion of ethanol via the tail vein yielded identical results indicating that the slower elimination rate in the C57BL/6J strain could not be the result of slower absorption across the gut wall. Infusion via the tail vein with radioactive sodium bicarbonate indicated that the DBA/2J strain has a higher rate of CO2 expiration (n.s.). Consequently, the higher rate of 14CO2 expiration from ethanol oxidation may not reflect a higher rate of metabolism. These results are discussed in terms of the apparent differences between these strains in neural sensitivity to ethanol.

A quantitative analysis of ethanol and acetaldehyde expired by inbred mouse strains

Expired ethanol and acetaldehyde were measured after an oral injection of ethanol in C57BL/6J and DBA/2J mouse strains by a combination of several techniques in a sequence involving a method for trapping expired radioactive compounds, separation of compounds by gas chromatography, isolation of radioactive ethanol and acetaldehyde, and their quantitative analysis by liquid scintillation spectrophotometry. With the specific activities used in evaluation of the technique (0.1 Ci/mole, acetaldehyde; 1.1 Ci/mol, ethanol) the lower limit of sensitivity using 500 microliters from a 10 ml trap is 955 pmoles for acetaldehyde and 101 pmoles for ethanol. However, in the animal experiments, injected ethanol has a specific activity of 1.1 Ci/mol which would make the specific activity of expired metabolically formed acetaldehyde the same. This results in a lower limit of sensitivity for acetaldehyde of 80 pmoles. The two strains were monitored for 80 min following an oral injection of 3.8 g/Kg of (2-14C) ethanol. Comparing the two strains on the expiration of each compound the curves were identical.

Butanediols: selection, open field activity, and NAD reduction by liver extracts in inbred mouse strains

Mice from the high-ethanol preferring C57BL strain and low-ethanol preferring DBA strain were tested for their preference for butanediols. The C57BL strain showed a significantly higher preference for a 10% (v/v) solution of 1,3-butanediol than the DBA strain. The C57BL strain also showed a significantly greater consumption of 1,2- and 2,3-butanediol, but the separation between strains was much smaller than with 1,3-butanediol. Both strains uniformly avoided 1,4-butanediol. Tolerance for 1,3-butanediol was tested in an open-field monitor at 3 doses. At the lowest dose the DBA strain was hyperactive and the C57BL were unaffected. At the highest dose both strains were equally depressed. The specific activity of NAD reduction on incubation of liver extracts with 1,3-butanediol and ethanol as substrates was higher with both compounds in extracts from the C57BL strain.

Voluntary selection of and tolerance to 1,2 propanediol (propylene glycol) by high and low ethanol-selecting mouse strains

Fifteen male mice from each of 4 inbred strains (C57BL/6J, BALB/cJ, CBA/J, and DBA/2J) were tested to determine their voluntary self-selection of a 10% solution of 1,2 propanediol (1,2 PD), A 3-carbon alcohol of low toxicity. As with ethanol, the C57BL/6J strain consumed significantly greater amounts that the 3 other low ethanol-selecting strains. A second experiment determined that the 3 low selecting strains suffered significantly greater depression of the central nervous system from 1,2 PD than the high selecting C57BL strain. It was also found that ethanol is a much more potent depressant that 1,2 PD. These results are discussed in terms of the possible role of neural sensitivity in regulating consumption levels of the 2 alcohols.