Auditory fear conditioning facilitates neurotransmitter release at lateral amygdala to basal amygdala synapses.

The lateral amygdala (LA) is a main sensory input site from the cortical and thalamic regions. In turn, LA glutamatergic pyramidal neurons strongly project to the basal amygdala (BA). Although it is well known that auditory fear conditioning involves synaptic potentiation in the LA, it is not clear whether the LA-BA synaptic transmission is modified upon auditory fear conditioning. Here we found that high-frequency stimulation ex vivo resulted in long-term potentiation (LTP) with a concomitant enhancement of neurotransmitter release at LA-BA synapses. Auditory fear conditioning also led to the presynaptic facilitation at LA-BA synapses. Meanwhile, AMPA/NMDA current ratio was not changed upon fear conditioning, excluding the involvement of postsynaptic mechanism. Notably, fear conditioning occluded electrically induced ex vivo LTP in the LA-BA pathway, indicating that the conditioning and electrically induced LTP share common mechanisms. Our findings suggest that the presynaptic potentiation of LA-BA synapses may be involved in fear conditioning.

Flexopiezoelectricity at ferroelastic domain walls in WO3 films.

The emergence of a domain wall property that is forbidden by symmetry in bulk can offer unforeseen opportunities for nanoscale low-dimensional functionalities in ferroic materials. Here, we report that the piezoelectric response is greatly enhanced in the ferroelastic domain walls of centrosymmetric tungsten trioxide thin films due to a large strain gradient of 106 m-1, which exists over a rather wide width (~20 nm) of the wall. The interrelationship between the strain gradient, electric polarity, and the electromechanical property is scrutinized by detecting of the lattice distortion using atomic scale strain analysis, and also by detecting the depolarized electric field using differential phase contrast technique. We further demonstrate that the domain walls can be manipulated and aligned in specific directions deterministically using a scanning tip, which produces a surficial strain gradient. Our findings provide the comprehensive observation of a flexopiezoelectric phenomenon that is artificially controlled by externally induced strain gradients.

Chronic social defeat stress increases burst firing of nucleus accumbens-projecting ventral subicular neurons in stress-susceptible mice.

The ventral subiculum (vSub) is the major output structure of the hippocampus and serves as a main limbic region in mediating the brain's response to stress. Previously, we reported that there are three subtypes of vSub neurons based on their firing patterns: regular-spiking (RS), weak-bursting (WB) and strong-bursting (SB) neurons and chronic social defeat stress (CSDS) increased SB neurons especially in the proximal vSub. Here, we found that neurons in the proximal vSub projected to the nucleus accumbens (NAc). CSDS significantly increased SB neurons but decreased RS neurons among the NAc-projecting vSub neuronal population. Interestingly, these changes were only apparent in mice susceptible to CSDS, but not in CSDS-resilient ones. Given that ventral hippocampal inputs to the NAc regulate susceptibility to CSDS, the bursting activity of NAc-projecting vSub neurons might be functionally relevant to behavioral susceptibility to CSDS.

Chronic social defeat stress-induced enhancement of T-type calcium channels increases burst-firing neurons in the ventral subiculum.

The ventral subiculum (vSub), a representative output structure of the hippocampus, serves as a main limbic region in mediating the brain's response to stress. There are three subtypes of subicular pyramidal neurons based on their firing patterns: regular-spiking (RS), weak-bursting (WB) and strong-bursting (SB) neurons, located differently along proximal-distal axis. Here, we found that chronic social defeat stress (CSDS) in mice increased the population of SB neurons but decreased RS neurons in the proximal vSub. Specific blockers of T-type calcium channels inhibited the burst firings with a concomitant reduction of afterdepolarization, suggesting that T-type calcium channels underlie the burst-spiking activity. Consistently, CSDS increased both T-type calcium currents and expression of Cav3.1 proteins, a subtype of T-type calcium channels, in the proximal vSub. Therefore, we conclude that CSDS-induced enhancement of Cav3.1 expression increased bursting neuronal population in the vSub, which may contribute to stress-related behaviors.

Differential regulation of neuronal excitability by nicotine and substance P in subdivisions of the medial habenula.

The medial habenula (MHb) plays an important role in nicotine-related behaviors, such as aversion and withdrawal. The MHb is composed of distinct subregions with unique neurotransmitter expression and neuronal connectivity. Here, we showed that nicotine and substance P (SP) differentially regulate neuronal excitability in subdivisions of the MHb (ventrolateral division, MHbVL; dorsal division; MHbD and superior division: MHbS). Nicotine remarkably increased spontaneous neuronal firing in the MHbVL and MHbD, but not in the MHbS, which was consistent with different magnitudes of whole-cell inward currents evoked by nicotine in each subdivision. Meanwhile, SP enhanced neuronal excitability in the MHbVL and MHbS. Although the MHbD is composed of SP-expressing neurons, they did not respond to SP. Neurons in the MHbVL increased their firing in response to bath-applied nicotine, which was attenuated by neurokinin receptor antagonists. Furthermore, nicotine addiction and withdrawal attenuated and augmented excitatory SP effects in the MHbVL, respectively. On the whole, we suggest that MHb-involving nicotine-related behaviors might be associated with SP signaling in MHb subdivisions.

Nanospherical solid electrolyte interface layer formation in binder-free carbon nanotube aerogel/Si nanohybrids to provide lithium-ion battery anodes with a long-cycle life and high capacity.

Silicon anodes for lithium ion batteries (LiBs) have been attracting considerable attention due to a theoretical capacity up to about 10 times higher than that of conventional graphite. However, huge volume expansion during the cycle causes cracks in the silicon, resulting in the degradation of cycling performance and eventual failure. Moreover, low electrical conductivity and an unstable solid electrolyte interface (SEI) layer resulting from repeated changes in volume still block the next step forward for the commercialization of the silicon material. Herein we demonstrate the carbon nanotube (CNT) aerogel/Si nanohybrid structure for anode materials of LiBs via freeze casting followed by an RF magnetron sputtering process, exhibiting improved capacity retention compared to Si only samples during 1000 electrochemical cycles. The CNT aerogels as 3D porous scaffold structures could provide buffer volume for the expansion/shrinkage of Si lattices upon cycling and increase electrical conductivity. In addition, the nanospherical and relatively thin SEI layers of the CNT aerogel/Si nanohybrid structure show better lithium ion diffusion characteristics during cycling. For this reason, the Si@CNT aerogel anode still yielded a high specific capacity of 1439 mA h g-1 after 1000 charge/discharge cycles with low capacity fading. Our approach could be applied to other group IV LiB materials that undergo large volume changes, and also has promising potential for high performance energy applications.

Observation of partial reduction of manganese in the lithium rich layered oxides, 0.4Li2MnO3-0.6LiNi1/3Co1/3Mn1/3O2, during the first charge.

Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large capacities. However, questions remain regarding the large irreversible loss in capacities for the first charge-discharge cycle due to oxygen removal in lattices related to layered Li2MnO3. Herein we present detailed studies on Li-rich Mn-based layered oxides of 0.4Li2MnO3-0.6LiNi1/3Co1/3Mn1/3O2 (Li-rich NCM) electrochemically activated between 2.5 V and 4.3 or 4.7 V vs. Li+/Li. Electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) revealed unusual manganese reduction after the first charge up to a high voltage of 4.7 V. Moreover, the electronic structure did not fully recover to the original pristine of Mn4+ state after discharge. Interestingly, these phenomena were not limited to a single particle, but were observed across the entire electrode. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and electron dispersive spectra (EDS) also showed a dramatic decline in oxygen content with highly porous morphologies, associated with oxygen vacancy formation following oxidation of O2- ions to O2. Our analysis suggests that an unstable manganese valence state with severe defects due to oxygen vacancies may lead to large irreversible capacity loss during the first charge-discharge cycle of Li-rich layered oxides.

Enhancement of the anisotropic photocurrent in ferroelectric oxides by strain gradients.

The phase separation of multiple competing structural/ferroelectric phases has attracted particular attention owing to its excellent electromechanical properties. Little is known, however, about the strain-gradient-induced electronic phenomena at the interface of competing structural phases. Here, we investigate the polymorphic phase interface of bismuth ferrites using spatially resolved photocurrent measurements, present the observation of a large enhancement of the anisotropic interfacial photocurrent by two orders of magnitude, and discuss the possible mechanism on the basis of the flexoelectric effect. Nanoscale characterizations of the photosensitive area through position-sensitive angle-resolved piezoresponse force microscopy and electron holography techniques, in conjunction with phase field simulation, reveal that regularly ordered dipole-charged domain walls emerge. These findings offer practical implications for complex oxide optoelectronics.

Thermal Cycling Behavior of Zinc Antimonide Thin Films for High Temperature Thermoelectric Power Generation Applications.

The zinc antimonide compound ZnxSby is one of the most efficient thermoelectric materials known at high temperatures due to its exceptional low thermal conductivity. For this reason, it continues to be the focus of active research, especially regarding its glass-like atomic structure. However, before practical use in actual surroundings, such as near a vehicle manifold, it is imperative to analyze the thermal reliability of these materials. Herein, we present the thermal cycling behavior of ZnxSby thin films in nitrogen (N2) purged or ambient atmosphere. ZnxSby thin films were prepared by cosputtering and reached a power factor of 1.39 mW m(-1) K(-2) at 321 °C. We found maximum power factor values gradually decreased in N2 atmosphere due to increasing resistivity with repeated cycling, whereas the specimen in air kept its performance. X-ray diffraction and electron microscopy observations revealed that fluidity of Zn atoms leads to nanoprecipitates, porous morphologies, and even growth of a coating layer or fiber structures on the surface of ZnxSby after repetitive heating and cooling cycles. With this in mind, our results indicate that proper encapsulation of the ZnxSby surface would reduce these unwanted side reactions and the resulting degradation of thermoelectric performance.

Thermal Spreading in Carbon Nanotube Coating.

Carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, have attracted significant attention as good candidates for next-generation heat-spreading materials because of their high thermal conductivity, mechanical flexibility, etc. Regarding the thermal spreading performance of carbon-based nanofilms, remarkable test results have been reported mainly from the industrial side, but their validity and the physical mechanism underlying the heat transfer enhancement are still under debate. In this study, we assess the thermal spreading performance of a multi-walled CNT film on a copper foil using a non-contact characterization method in a simple and methodical manner, and discuss the possibility of carbon nanofilms as heat spreaders based on the experimental and numerical results. This study provides useful information on heat transfer enhancement by carbon nanofilms and could contribute to the development of high-performance carbon-based heat-spreading coatings.

Tensile testing of ultra-thin films on water surface.

The surface of water provides an excellent environment for gliding movement, in both nature and modern technology, from surface living animals such as the water strider, to Langmuir-Blodgett films. The high surface tension of water keeps the contacting objects afloat, and its low viscosity enables almost frictionless sliding on the surface. Here we utilize the water surface as a nearly ideal underlying support for free-standing ultra-thin films and develop a novel tensile testing method for the precise measurement of mechanical properties of the films. In this method, namely, the pseudo free-standing tensile test, all specimen preparation and testing procedures are performed on the water surface, resulting in easy handling and almost frictionless sliding without specimen damage or substrate effects. We further utilize van der Waals adhesion for the damage-free gripping of an ultra-thin film specimen. Our approach can potentially be used to explore the mechanical properties of emerging two-dimensional materials.