Effect of the Degree of Li3PO4 Vapor Dissociation on the Ionic Conductivity of LiPON Thin Films

Thin films of solid-state lithium-ion electrolytes show promise for use in small-sized autonomous power sources for micro- and nanoelectronic elements. The high rate of vacuum-plasma synthesis (~0.5 μm/h) of lithium phosphor-oxynitride (LiPON) films with an ionic conductivity of ~2·10-6 S/cm is achieved through anodic evaporation of Li3PO4 in a low-pressure arc. The microstructure and ionic conductivity of LiPON films are influenced by the proportion of free lithium in the vapor flow. This paper presents the results of a study on the plasma composition during anodic evaporation of Li3PO4 in a discharge with a self-heating hollow cathode and a crucible anode. A method is proposed for adjusting the free lithium concentration in the gas-vapor (Li3PO4 + N2/Ar) discharge plasma based on changing the frequency of collisions of electrons with Li3PO4 vapor in the anodic region of the discharge. It is demonstrated that an increase in the proportion of free lithium in the flow of deposited particles leads to an enhancement in the concentration and mobility of lithium ions in the deposited films and, subsequently, an improvement in the ionic conductivity of LiPON films.

Exciton Luminescence and Optical Properties of Nanocrystalline Cubic Y2O3 Films Prepared by Reactive Magnetron Sputtering

This paper presents a comprehensive study of the energy structure, optical characteristics, and spectral-kinetic parameters of elementary excitations in a high-purity nanocrystalline cubic Y₂O₃ film synthesized by reactive magnetron sputtering. The optical transparency gaps for direct and indirect interband transitions were determined and discussed. The dispersion of the refractive index was established based on the analysis of interference effects. It was found that the refractive index of the Y₂O₃ film synthesized in this study is higher in order of magnitude than that of the films obtained with the help of other technologies. The intrinsic emission of Y₂O₃ film has been discussed and associated with the triplet-singlet radiative relaxation of self-trapped and bound excitons. We also studied the temperature behavior of the exciton luminescence of Y₂O₃ for the first time and determined thermal activation barriers. The optical energy and kinetic parameters of cubic Y₂O₃ films were analyzed in comparison with those of the monoclinic films of yttrium oxide. The main difference between the optical properties of cubic and monoclinic Y₂O₃ films was established, which allowed for a supposition of their application prospects.

Attenuation of the extracellular matrix increases the number of synapses but suppresses synaptic plasticity through upregulation of SK channels

The effect of brain extracellular matrix (ECM) on synaptic plasticity remains controversial. Here, we show that targeted enzymatic attenuation with chondroitinase ABC (ChABC) of ECM triggers the appearance of new glutamatergic synapses on hippocampal pyramidal neurons, thereby increasing the amplitude of field EPSPs while decreasing both the mean miniature EPSC amplitude and AMPA/NMDA ratio. Although the increased proportion of 'unpotentiated' synapses caused by ECM attenuation should promote long-term potentiation (LTP), surprisingly, LTP was suppressed. The upregulation of small conductance Ca²⁺-activated K⁺ (SK) channels decreased the excitability of pyramidal neurons, thereby suppressing LTP. A blockade of SK channels restored cell excitability and enhanced LTP; this enhancement was abolished by a blockade of Rho-associated protein kinase (ROCK), which is involved in the maturation of dendritic spines. Thus, targeting ECM elicits the appearance of new synapses, which can have potential applications in regenerative medicine. However, this process is compensated for by a reduction in postsynaptic neuron excitability, preventing network overexcitation at the expense of synaptic plasticity.

Astrocytic Coverage of Dendritic Spines, Dendritic Shafts, and Axonal Boutons in Hippocampal Neuropil

Distal astrocytic processes have a complex morphology, reminiscent of branchlets and leaflets. Astrocytic branchlets are rod-like processes containing mitochondria and endoplasmic reticulum, capable of generating inositol-3-phosphate (IP₃)-dependent Ca²⁺ signals. Leaflets are small and flat processes that protrude from branchlets and fill the space between synapses. Here we use three-dimensional (3D) reconstructions from serial section electron microscopy (EM) of rat CA1 hippocampal neuropil to determine the astrocytic coverage of dendritic spines, shafts and axonal boutons. The distance to the maximum of the astrocyte volume fraction (VF) correlated with the size of the spine when calculated from the center of mass of the postsynaptic density (PSD) or from the edge of the PSD, but not from the spine surface. This suggests that the astrocytic coverage of small and larger spines is similar in hippocampal neuropil. Diffusion simulations showed that such synaptic microenvironment favors glutamate spillover and extrasynaptic receptor activation at smaller spines. We used complexity and entropy measures to characterize astrocytic branchlets and leaflets. The 2D projections of astrocytic branchlets had smaller spatial complexity and entropy than leaflets, consistent with the higher structural complexity and less organized distribution of leaflets. The VF of astrocytic leaflets was highest around dendritic spines, lower around axonal boutons and lowest around dendritic shafts. In contrast, the VF of astrocytic branchlets was similarly low around these three neuronal compartments. Taken together, these results suggest that astrocytic leaflets preferentially contact synapses as opposed to the dendritic shaft, an arrangement that might favor neurotransmitter spillover and extrasynaptic receptor activation along dendritic shafts.

Subcellular location of astrocytic calcium stores favors extrasynaptic neuron-astrocyte communication

Neuron-astrocyte interactions are important for brain computations and synaptic plasticity. Perisynaptic astrocytic processes (PAPs) contain a high density of transporters that are responsible for neurotransmitter clearance. Metabotropic glutamate receptors are thought to trigger Ca(2+) release from Ca(2+) stores in PAPs in response to synaptic activity. Our ultrastructural study revealed that PAPs are actually devoid of Ca(2+) stores and have a high surface-to-volume ratio favorable for uptake. Astrocytic processes containing Ca(2+) stores were located further away from the synapses and could therefore respond to changes in ambient glutamate. Thus, the anatomic data do not support communication involving Ca(2+) stores in tripartite synapses, but rather point to extrasynaptic communication.

[Thymectomy for myastenia gravis: 25-year experience]

OBJECTIVE

Thymectomy is considered an effective therapeutic option for patients with myasthenia gravis (MG). We reviewed our 25-years experience with surgical treatment of MG with respect to long-term results and factors affecting outcome.

METHODS

Between 1978 and 2002, we performed 232 thymectomies for MG. Fifteen patients were lost to follow-up; the remaining 217 form the object of our study. 32 patients (28.4%) had thymoma. Myasthenia was graded according to a modified Osserman classification: 51 patients (23.5%) were in class I, 81 (37.3%) in class IIA, 52 (24%) in class IIB, 26 (12%) in class III and seven (3.2%) in class IV. Mean duration of symptoms before the operation was 14 +/- 10 months. Fifty-eight thymectomies for thymoma were performed through a median sternotomy and four through a clamshell incision. Forty-six thymectomies for non-thymomatous MG were performed through a standard cervicotomy, 155 procedures through a partial upper sternal-splitting incision and eight through a complete median sternotomy.

RESULTS

Operative mortality was 0.92% (two patients). After a mean follow-up of 119 months, 77% of all patients improved their clinical status (26% without medications and asymptomatic; 45% with a reduction of medications and/or clinically improved); 39 (18%) have a stable disease with no clinical modifications; 12 (5%) presented a deterioration of their clinical status with worse symptoms, required more medications, or both. Thirteen patients (6%) died because of MG (mean survival 34.3 +/- 3.6 months). The presence of a thymoma negatively influenced the prognosis. Younger patients showed a more favorable outcome as well as patients with a shorter duration of symptoms before the operation; patients with lower classes of myasthenia showed a higher rate of remission.

CONCLUSIONS

Thymectomy is effective in the management of patients with MG at all stages with low morbidity. Patients with thymoma present a less favorable outcome.