Polyethylene glycol-fused allografts produce rapid behavioral recovery after ablation of sciatic nerve segments.

Restoration of neuronal functions by outgrowths regenerating at ∼1 mm/day from the proximal stumps of severed peripheral nerves takes many weeks or months, if it occurs at all, especially after ablation of nerve segments. Distal segments of severed axons typically degenerate in 1-3 days. This study shows that Wallerian degeneration can be prevented or retarded, and lost behavioral function can be restored, following ablation of 0.5-1-cm segments of rat sciatic nerves in host animals. This is achieved by using 0.8-1.1-cm microsutured donor allografts treated with bioengineered solutions varying in ionic and polyethylene glycol (PEG) concentrations (modified PEG-fusion procedure), being careful not to stretch any portion of donor or host sciatic nerves. The data show that PEG fusion permanently restores axonal continuity within minutes, as initially assessed by action potential conduction and intracellular diffusion of dye. Behavioral functions mediated by the sciatic nerve are largely restored within 2-4 weeks, as measured by the sciatic functional index. Increased restoration of sciatic behavioral functions after ablating 0.5-1-cm segments is associated with greater numbers of viable myelinated axons within and distal to PEG-fused allografts. Many such viable myelinated axons are almost certainly spared from Wallerian degeneration by PEG fusion. PEG fusion of donor allografts may produce a paradigm shift in the treatment of peripheral nerve injuries.

Photon-enhanced thermionic emission from heterostructures with low interface recombination.

Photon-enhanced thermionic emission is a method of solar-energy conversion that promises to combine photon and thermal processes into a single mechanism, overcoming fundamental limits on the efficiency of photovoltaic cells. Photon-enhanced thermionic emission relies on vacuum emission of photoexcited electrons that are in thermal equilibrium with a semiconductor lattice, avoiding challenging non-equilibrium requirements and exotic material properties. However, although previous work demonstrated the photon-enhanced thermionic emission effect, efficiency has until now remained very low. Here we describe electron-emission measurements on a GaAs/AlGaAs heterostructure that introduces an internal interface, decoupling the basic physics of photon-enhanced thermionic emission from the vacuum emission process. Quantum efficiencies are dramatically higher than in previous experiments because of low interface recombination and are projected to increase another order of magnitude with more stable, low work-function coatings. The results highlight the effectiveness of the photon-enhanced thermionic emission process and demonstrate that efficient photon-enhanced thermionic emission is achievable, a key step towards realistic photon-enhanced thermionic emission based energy conversion.

Prolongation of the QT interval by volatile anesthetics in chronically instrumented dogs.

The influence of volatile anesthetics on ventricular repolarization in vivo (QT interval) has not been studied in a systematic fashion. The purpose of this investigation was to characterize the electrocardiographic and hemodynamic actions of the volatile anesthetics halothane, isoflurane, and enflurane in chronically instrumented dogs. Because autonomic nervous system tone may influence ECG findings, experiments were completed with and without concomitant pharmacologic autonomic nervous system blockade. In six groups comprising 50 experiments with 21 instrumented dogs, anesthesia was mask-induced with nitrous oxide, oxygen, and one of the volatile anesthetics and maintained with the volatile anesthetic in 100% oxygen for 2 hours. Changes in the ECG and in hemodynamics were compared to the conscious state. In the absence of autonomic nervous system blockade, halothane and isoflurane significantly prolonged the QT interval (0.24 +/- 0.01 to 0.30 +/- 0.01 second and 0.22 +/- 0.01 to 0.28 +/- 0.01 second, respectively), whereas enflurane produced no change in ventricular repolarization (0.24 +/- 0.01 to 0.26 +/- 0.01 second). All of the volatile anesthetics increased the QT interval corrected for changes in basal heart rate (QTc), and all agents decreased intravascular pressure and dP/dt. Following autonomic nervous system blockade, halothane, isoflurane, and enflurane significantly increased the QT interval and QTc. The results demonstrate that ventricular repolarization is directly altered by the volatile anesthetics independent of changes in autonomic nervous tone. Whether or not such effects are additive with other congenital or acquired forms of QTc prolongation has yet to be examined. The present results indicate that caution should be used during the administration of volatile anesthetics to patients with abnormalities of the QT interval.

Specific bradycardic agents, a new therapeutic modality for anesthesiology: hemodynamic effects of UL-FS 49 and propranolol in conscious and isoflurane-anesthetized dogs.

A "specific bradycardic agent" has direct negative chronotropic actions without producing other systemic or coronary hemodynamic alterations. UL-FS 49, a recently synthesized structural analog of verapamil without classical slow channel calcium blocking activity, is proposed as such an agent. The purpose of this investigation was to characterize the hemodynamic and electrocardiographic actions of UL-FS 49 (0.25, 0.50, and 1.0 mg/kg) and compare its effects with those of propranolol (0.25, 0.50, and 1.0 mg/kg) in conscious or isoflurane-anesthetized (with and without neuromuscular blockade by pancuronium) chronically instrumented dogs. In six groups, comprising 52 experiments, UL-FS 49 was found to be more efficacious than propranolol in reducing heart rate, although this agent did not block the hemodynamic response to isoproterenol. UL-FS 49 produced 45-50% reductions in heart rate in dogs with isoflurane-induced tachycardia as compared to 15 and 30% reductions following propranolol. Furthermore, few other hemodynamic alterations were produced by UL-FS 49 indicating the remarkable specificity of this drug for reducing heart rate. A "specific bradycardic agent" such as UL-FS 49 may be useful clinically during the perioperative period. Such a drug may be especially advantageous for patients with documented or suspected ischemic heart disease, those who cannot tolerate the side effects of beta adrenergic blockade, as well as patients requiring a greater reduction in heart rate than can be obtained with beta adrenergic receptor antagonists.