Regional synapse gain and loss accompany memory formation in larval zebrafish.

Defining the structural and functional changes in the nervous system underlying learning and memory represents a major challenge for modern neuroscience. Although changes in neuronal activity following memory formation have been studied [B. F. Grewe et al., Nature 543, 670-675 (2017); M. T. Rogan, U. V. Stäubli, J. E. LeDoux, Nature 390, 604-607 (1997)], the underlying structural changes at the synapse level remain poorly understood. Here, we capture synaptic changes in the midlarval zebrafish brain that occur during associative memory formation by imaging excitatory synapses labeled with recombinant probes using selective plane illumination microscopy. Imaging the same subjects before and after classical conditioning at single-synapse resolution provides an unbiased mapping of synaptic changes accompanying memory formation. In control animals and animals that failed to learn the task, there were no significant changes in the spatial patterns of synapses in the pallium, which contains the equivalent of the mammalian amygdala and is essential for associative learning in teleost fish [M. Portavella, J. P. Vargas, B. Torres, C. Salas, Brain Res. Bull 57, 397-399 (2002)]. In zebrafish that formed memories, we saw a dramatic increase in the number of synapses in the ventrolateral pallium, which contains neurons active during memory formation and retrieval. Concurrently, synapse loss predominated in the dorsomedial pallium. Surprisingly, we did not observe significant changes in the intensity of synaptic labeling, a proxy for synaptic strength, with memory formation in any region of the pallium. Our results suggest that memory formation due to classical conditioning is associated with reciprocal changes in synapse numbers in the pallium.

Regulation of Lead Iodide Crystallization and Distribution for Efficient Perovskite Solar Cells.

At present, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has reached 26.1%. Polycrystalline perovskite films prepared by sequential deposition are often accompanied by excess PbI2. Although excess PbI2 can reduce the internal defects of the perovskites and promote charge transfer, excess PbI2 is unevenly distributed in the perovskites and easily decomposed into the composite center of charge. Therefore, the growth and distribution of PbI2 crystals can be regulated by introducing 4-fluoroaniline (4-FLA) as an additive into the precursor of PbI2. We observe that the presence of an amino group in 4-FLA leads to a reduction in the strength of van der Waals forces between PbI2 layer structures, thereby facilitating the uniform dispersion of excess PbI2 within the perovskites. Additionally, 4-FLA is restricted from being embedded in the PbI2 layer due to the steric hindrance of 4-FLA and the hydrogen bond interaction between nitrogen atoms and PbI2. Therefore, it leads to better dispersion of PbI2, resulting in better passivation and device efficiency. Based on the hydrophobicity of the benzene ring, the modified perovskite film shows excellent hydrophobicity. Ultimately, we achieved 21.63% PCE and 1.16V VOC. This provides an effective strategy for regulating excess PbI2 to achieve efficient and stable PSCs.

Slow-Release Effect Assisted Crystallization for Sequential Deposition Realizes Efficient Inverted Perovskite Solar Cells.

The two-step sequential deposition strategy has been widely recognized in promoting the research and application of perovskite solar cells, but the rapid reaction of organic salts with lead iodide inevitably affects the growth of perovskite crystals, accompanied by the generation of more defects. In this study, the regulation of crystal growth was achieved in a two-step deposition method by mixing 1-naphthylmethylammonium bromide (NMABr) with organic salts. The results show that the addition of NMABr effectively delays the aggregation and crystallization behavior of organic salts; thereby, the growth of the optimal crystal (001) orientation of perovskite is promoted. Based on this phenomenon of delaying the crystallization process of perovskite, the "slow-release effect assisted crystallization" is defined. Moreover, the incorporation of the Br element expands the band gap of perovskite and mitigates material defects as nonradiative recombination centers. Consequently, the power conversion efficiency (PCE) of the enhanced perovskite solar cells (PSCs) reaches 20.20%. It is noteworthy that the hydrophobic nature of the naphthalene moiety in NMABr can enhance the humidity resistance of PSCs, and the perovskite phase does not decompose for more than 3000 h (30-40% RH), enabling it to retain 90% of its initial efficiency even after exposure to a nitrogen environment for 1200 h.

Amino Pyridine Iodine as an Additive for Defect-Passivated Perovskite Solar Cells.

Defect passivation of the perovskite surface and grain boundary (GBs) has become a widely adopted approach to reduce charge recombination. Research has demonstrated that functional groups with Lewis acid or base properties can successfully neutralize trap states and limit nonradiative recombination. Unlike traditional Lewis acid-base organic molecules that only bind to a single anionic or cationic defect, zwitterions can passivate both anionic and cationic defects simultaneously. In this work, zwitterions organic halide salt 1-amino pyridine iodine (AmPyI) is used as a perovskite for defect passivation. It is found that a pair of amino lone electrons in AmPyI can passivate defects surface and GBs through hydrogen bonding with perovskite, and the introduced I- can bind to uncoordinated Pb2+ while also controlling the surface morphology of the film and improving the crystallinity. In the presence of the AmPyI additive, we obtained about 1.24 µm of amplified perovskite grains and achieved an efficiency of 23.80% with minimal hysteresis.

Alteration of GABAergic neurotransmission in Huntington's disease.

Hereditary Huntington's disease (HD) is characterized by cell dysfunction and death in the brain, leading to progressive cognitive, psychiatric, and motor impairments. Despite molecular and cellular descriptions of the effects of the HD mutation, no effective pharmacological treatment is yet available. In addition to well-established alterations of glutamatergic and dopaminergic neurotransmitter systems, it is becoming clear that the GABAergic systems are also impaired in HD. GABA is the major inhibitory neurotransmitter in the brain, and GABAergic neurotransmission has been postulated to be modified in many neurological and psychiatric diseases. In addition, GABAergic neurotransmission is the target of many drugs that are in wide clinical use. Here, we summarize data demonstrating the occurrence of alterations of GABAergic markers in the brain of HD carriers as well as in rodent models of the disease. In particular, we pinpoint HD-related changes in the expression of GABAA receptors (GABAA Rs). On the basis that a novel GABA pharmacology of GABAA Rs established with more selective drugs is emerging, we argue that clinical treatments acting specifically on GABAergic neurotransmission may be an appropriate strategy for improving symptoms linked to the HD mutation.

Differential Alteration in Expression of Striatal GABAAR Subunits in Mouse Models of Huntington's Disease.

Huntington's disease (HD) is a neurodegenerative disorder characterized by progressive motor symptoms that are preceded by cognitive deficits and is considered as a disorder that primarily affects forebrain striatal neurons. To gain a better understanding of the molecular and cellular mechanisms associated with disease progression, we analyzed the expression of proteins involved in GABAergic neurotransmission in the striatum of the R6/1 transgenic mouse model. Western blot, quantitative PCR and immunohistochemical analyses were conducted on male R6/1 mice and age-matched wild type littermates. Analyses were performed on 2 and 6 month-old animals, respectively, before and after the onset of motor symptoms. Expression of GAD 67, GAD 65, NL2, or gephyrin proteins, involved in GABA synthesis or synapse formation did not display major changes. In contrast, expression of α1, α3 and α5 GABAAR subunits was increased while the expression of δ was decreased, suggesting a change in tonic- and phasic inhibitory transmission. Western blot analysis of the striatum from 8 month-old Hdh Q111, a knock-in mouse model of HD with mild deficits, confirmed the α1 subunit increased expression. From immunohistochemical analyses, we also found that α1 subunit expression is increased in medium-sized spiny projection neurons (MSN) and decreased in parvalbumin (PV)-expressing interneurons at 2 and 6 months in R6/1 mice. Moreover, α2 subunit labeling on the PV and MSN cell membranes was increased at 2 months and decreased at 6 months. Alteration of gene expression in the striatum and modification of GABAA receptor subtypes in both interneurons and projection neurons suggested that HD mutation has a profound effect on synaptic plasticity at an early stage, before the onset of motor symptoms. These results also indicate that cognitive and other behavioral deficits may be associated with changes in GABAergic neurotransmission that consequently could be a relevant target for early therapeutic treatment.

Early GABAergic transmission defects in the external globus pallidus and rest/activity rhythm alteration in a mouse model of Huntington's disease.

Huntington's disease (HD) is characterized by progressive motor symptoms preceded by cognitive deficits and is regarded as a disorder that primarily affects the basal ganglia. The external globus pallidus (GPe) has a central role in the basal ganglia, projects directly to the cortex, and is majorly modulated by GABA. To gain a better understanding of the time course of HD progression and gain insight into the underlying mechanisms, we analyzed GABAergic neurotransmission in the GPe of the R6/1 mouse model at purportedly asymptomatic and symptomatic stages (i.e., 2 and 6months). Western blot and quantitative polymerase chain reaction (PCR) analyses revealed alterations in the GPe of male R6/1 mice compared with wild-type littermates. Expression of proteins involved in pre- and post-synaptic GABAergic compartments as well as synapse number were severely decreased at 2 and 6months. At both ages, patch-clamp electrophysiological recordings showed a decrease of spontaneous and miniature inhibitory post-synaptic currents (IPSCs) suggesting that HD mutation has an early effect on the GABA signaling in the brain. Therefore, we performed continuous locomotor activity recordings from 2 to 4months of age. Actigraphy analyses revealed rest/activity fragmentation alterations that parallel GABAergic system impairment at 2months, while the locomotor deficit is evident only at 3months in R6/1 mice. Our results reveal early deficits in HD and support growing evidence for a critical role played by the GPe in physiological and pathophysiological states. We suggest that actimetry may be used as a non-invasive tool to monitor early disease progression.

Chronic cannabinoid receptor stimulation selectively prevents motor impairments in a mouse model of Huntington's disease.

Huntington's disease (HD) is a devastating neurodegenerative disease characterized by a progressive decline in motor abilities, as well as in cognitive and social behaviors. Most of these behavioral deficits are recapitulated in the R6/1 transgenic mouse, which can therefore be used as an experimental model to identify the neurobiological substrates of HD pathology and to design novel therapeutic approaches. The endocannabinoid system (ECS) is a relevant candidate to participate in the etiopathology of HD as it is a key modulator of brain function, especially in areas primarily affected by HD dysfunction such as the striatum. Thus, some studies have demonstrated an association between HD progression and alterations in the expression of several ECS elements, thereby suggesting that improving ECS function may constitute a useful strategy to eliminate or at least delay the appearance of HD symptoms. Here this hypothesis was specifically tested by evaluating whether the administration of a well-characterized cannabinoid receptor agonist (WIN 55,212), either acutely or chronically, improves the HD-like symptoms in R6/1 mice. While acute treatment did not change the behavioral phenotype of transgenic animals, chronic administration was able to prevent the appearance of motor deficits, to increase the number of striatal huntingtin inclusions and to prevent the loss of striatal medium-sized spiny neurons, without affecting the social or cognitive alterations. These findings suggest that prolonged administration of cannabinoid receptor agonists could be an appropriate strategy for selectively improving motor symptoms and stimulating neuroprotective processes in HD patients.

Transition metals-based electrocatalysts on super-flat substrate for perovskite photovoltaic hydrogen production with 13.75% solar to hydrogen efficiency.

Harnessing the inexhaustible solar energy for water splitting is regarded one of the most promising strategies for hydrogen production. However, sluggish kinetics of oxygen evolution reaction (OER) and expensive photovoltaics have hindered commercial viability. Here, an adhesive-free electrodeposition process is developed for in-situ preparation of earth-abundant electrocatalysts on super-flat indium tin oxide (ITO) substrate. NiFe hydroxide exhibited prominent OER performance, achieving an ultra-low overpotential of 236 mV at 10 mA/cm2 in alkaline solution. With the superior OER activity, we achieved an unassisted solar water splitting by series connected perovskite solar cells (PSCs) of 2 cm2 aperture area with NiFe/ITO//Pt electrodes, yielding overall solar to hydrogen (STH) efficiency of 13.75 %. Furthermore, we upscaled the monolithic facility to utilize perovskite solar module for large-scale hydrogen production and maintained an approximate operating current of 20 mA. This creative strategy contributes to the decrease of industrial manufacturing expenses for perovskite-based photovoltaic-electrochemical (PV-EC) hydrogen production, further accelerating the conversion and utilization of carbon-free energy.