Synaptic plasticity is the process by which long-lasting changes take place at synaptic connections. The phenomenon itself is complex and can involve many levels of organization. Some authors separate forms into adaptations that have positive or negative consequences for the individual. It has been hypothesized that an increase in the number of synapses may represent a structural basis for the enduring expression of synaptic plasticity during some events that involve memory and learning; also, it has been suggested that perforated synapses increase in number after some diseases and experimental situations. The aim of this study was to analyze whether dopamine depletion induces changes in the synaptology of the corpus striatum of rats after the unilateral injection of 6-OHDA. The findings suggest that after the lesion, both contralateral and ipsilateral striata exhibit an increased length of the synaptic ending in ipsilateral (since third day) and contralateral striatum (since Day 20), loss of axospinous synapses in ipsilateral striatum and a significant increment in the number of perforated synapses, suggesting brain plasticity that might be deleterious for the spines, because this type of synaptic contacts are presumably excitatory, and in the absence of the modulatory effects of dopamine, the neuron could die through excitotoxic mechanisms. Thus, we can conclude that the presence of perforated synapses after striatal dopamine depletion might be a form of maladaptive synaptic plasticity.

Formation of nanoscale helium (He) bubbles in reduced activation ferritic/martensitic steels may lead to degradation of mechanical properties of materials. Transmission electron microscopy (TEM) has commonly been used to image the Fresnel contrast of He bubbles, using an underfocus of 0.5-1µm. This paper presents our study of multislice simulation of the size correlation between imaged Fresnel rings and the actual He bubbles. It was found that for bubbles equal to or >3nm in diameter, the imaged bubble size, represented by its inner diameter of the first dark Fresnel ring (D(in)) in underfocused imaging conditions, increases with increasing electron-beam incoherency, but decreases with increasing underfocus. The electron-beam accelerating voltage, bubble size, bubble position and TEM sample thickness were found to have no significant influence on the deviation of D(in) from the actual bubble size (D(0)). However, for bubbles equal to or <2nm, D(in)/D(0) increases dramatically with increasing underfocus when it is above a threshold limit (e.g. Δf=-1µm for a 2-nm bubble). The results of this study also suggested that He bubbles can be differentiated from argon (Ar) bubbles by contrast differences.

The dry weight of tendon tissue is accounted for mainly by collagen fibers. Accordingly, the tendon-healing process primarily involves repair of collagen fibers. During the remodeling phase of tendon healing, newly proliferating collagen fibers are transformed into a mature repaired tendon. Despite the importance of this phenomenon, the details of fibrous rebuilding have not been reported previously. The aim of this study was to visualize the ultrastructural changes and to obtain a clear understanding of the reorganization of the collagen fibers in the tendon repair site, using rat Achilles tendons. We used scanning electron microscopy (SEM) with cell maceration as the main method of analysis. Pretreatment with cell maceration removed the cellular components successfully. This allowed precise visualization of each collagen fiber and the three-dimensional network of the fibers. This study was the first to apply the cell-maceration/SEM method to observe tendon tissue. Seven days after surgery, new collagen fibers grew extensively in the repair site in a random arrangement. Fourteen days after surgery, the collagen fibers began to form an axial arrangement. Near the tendon stump, this change progressed from the outer layer to the core region. On the other hand, in the middle of the repair site, it progressed from the core to the outer layer. Change in the axial arrangement of collagen fibers contributes to the connection between the repair site and the tendon stump and to the separation of the repair site from the paratenon.

Journal Article JEM in this issue, 61:4 Get access Journal of Electron Microscopy, Volume 61, Issue 4, August 2012, Page NP, https://doi.org/10.1093/jmicro/dfs020 Published: 01 August 2012

Simulations were carried out for the orbit of electron-induced secondary electrons around a charged microfibril of a sciatic nerve tissue. In order to set the parameters for the simulation, the shape of the microfibril was determined from a transmission electron microscopy image, while the electric potential on the surface of the charged microfibril was evaluated from a reconstructed phase image obtained with electron holography. On the other hand, the passing point and the angle of secondary electrons at the microfibril surface were determined from a reconstructed amplitude image. Eventually, simulation of orbits of secondary electrons was carried out by changing the kinetic energy of the secondary electrons. Under the given conditions, the orbit of secondary electrons with a kinetic energy of 29.6eV fits the observations. If there are thin layers of electrons, the secondary electrons do not reach the surface but they go over it due to the repulsive Coulomb force resulting in successive revolving motion around the charged microfibril. Furthermore, the electric field variation due to the movement of the electric charges resulting from the specimen drift is also discussed briefly comparing it with electron holography data.

The nonuniformity in hydride vapor phase epitaxy (HVPE)-grown thick GaN was studied using cathodoluminescence (CL) technique. It was found that the nonuniform luminescence feature originated from pit-type defects. Two kinds of pit-type defects were distinguished by their morphology: one was hexagonal V-pit surrounded by {10−11} facets and the other was U-pit with {10−11} facets and the blunt bottom. The {10−11} facets of both pits with N-polarity show the strong CL emission due to the oxygen incorporation, while the matrix with Ga-polarity appeared dark in the CL image. The dim CL contrast was observed in the blunt bottom with the mixed polarities. The blunt bottom suggests the filling of pits during the growth, which may be the key to eliminate pit-type defects in free-standing GaN wafer.

A new grating (JS50XL) for ultrasoft-X-ray spectroscopy in an energy range 50–200 eV was designed, manufactured and tested. A spectrometer composed of the grating and a multi-channel plate detector was constructed. At the low-energy end of this spectrometer, a sharp Fermi edge of Mg-L emission was observed at 49.5 eV with an energy resolution of 0.15 eV. Li-K emission spectra were obtained from metal-Li, surface-oxidized metal-Li and 5% Li–Al. Relative energy shifts observed in Al-L emission spectra of Al, AlN and MgAl2O4 were explained by shifts in core binding energies (chemical shift) and bandgap energies of those materials. Si-L emissions from Si, SiC and SiO2 (quartz) and P-L emissions from GaP and InP were presented. Furthermore, the grating was tilted to extend the lower limit of detection energy to 32 eV, and the whole intensity distribution of Mg-L emission was successfully obtained. These ultrasoft-X-ray emission spectra show a successful extension to lower-energy range using the new soft-X-ray emission spectroscopy instrument in electron microscopy.

In order to obtain a large deflection angle without increasing the applied voltage to an electron biprism, we have developed a 'twin-electron biprism' (TBP), which is composed of two filament electrodes and a pair of ground plates. The observed interference-fringe spacing revealed that the deflection angle created by a TBP was about twice larger than that by a 'conventional electron biprism'. Also, we have suggested, in a double-electron biprism interferometry, the optimal disposition of a TBP for reducing the intensity of Fresnel fringes recorded in an electron hologram.

Noise is a primary issue in obtaining an image in a scanning microscope. This noise needs to be minimized in order to have a clear image of the sample in case of a nanosize level measurement. In this work, we propose a method to improve the image quality by applying dither signal injection to the scanning signal. This method involves minimizing the noise that occurs in scan control circuits, which results in a blurry or distorted image. The collected secondary electrons are first multiplied through a photomultiplier tube and are then converted into digital form using an analog/digital (A/D) converter. We propose a solution for the noise from the scan control circuit that appears on the image by adopting the spread spectrum method.