Faculty Bibliography

BACKGROUND:Ischemia can induce rapid activation of microglia in the brain. As key immunocompetent cells, reactive microglia play an important role in pathological development of ischemic stroke. However, the role of activated microglia during the development of ischemia remains controversial. Thus, we aimed to investigate the function of reactive microglia in the early stage of ischemic stroke. METHODS:mice were used to specifically deplete resident microglia through intragastric administration of tamoxifen (Ta) and intraperitoneal injection of diphtheria toxin (DT). At day 3 after ischemic stroke, behavioral tests were performed. After that, mouse brains were collected for further histological analysis and detection of mRNA expression of inflammatory factors. RESULTS:) cells. Importantly, depleting microglia induced a significant increase in the mRNA expression level of anti-inflammatory factors TGF-β1, Arg1, IL-10, IL-4, and Ym1 as well as a significant decline of pro-inflammatory factors TNF-α, iNOS, and IL-1β 3 days after stroke. CONCLUSIONS:These results suggest that activated microglia is an important modulator of the brain's inflammatory response in stroke, contributing to neurological deficit and infarct expansion. Modulation of the inflammatory response through the elimination of microglia at a precise time point may be a promising therapeutic approach for the treatment of cerebral ischemia.

Hydrodynamic drag not only results in high-energy consumption for water vehicles but also impedes the increase of vehicle speed. The introduction of a low-viscosity gas lubricating film is assumed to be an effective and promising method to reduce hydrodynamic drag. However, the poor stability of the gas film and massive extra energy consumption restricts the practical application of the gas lubricating method. Herein, inspired by the microhairs with low surface energy wax covering the abdomen of water spiders, superhydrophobic sphere surfaces were designed. Attributed to numerous neighboring nanoneedle branches with low surface energy chemicals, an air-entrained cavity with a large surface area was captured and stabilized by the superhydrophobic sphere, changing its shape from a sphere to a streamlined body. The cavity continued attaching to the superhydrophobic sphere without bursting at a depth of 70.0-90.0 cm underwater and reduced the hydrodynamic drag by more than 90%. This work provides a simple, cost-effective, and energy-efficient way to stabilize the underwater gas-liquid interface to achieve a reduction in the hydrodynamic drag.

Perturbed neuronal Ca²⁺ homeostasis is implicated in Alzheimer's disease, which has primarily been demonstrated in mice with amyloid-β deposits but to a lesser and more variable extent in tauopathy models. In this study, we injected AAV to express Ca²⁺ indicator in layer II/III motor cortex neurons and measured neuronal Ca²⁺ activity by two photon imaging in awake transgenic JNPL3 tauopathy and wild-type mice. Various biochemical measurements were conducted in postmortem mouse brains for mechanistic insight and a group of animals received two intravenous injections of a tau monoclonal antibody spaced by four days to test whether the Ca²⁺ dyshomeostasis was related to pathological tau protein. Under running conditions, we found abnormal neuronal Ca²⁺ activity in tauopathy mice compared to age-matched wild-type mice with higher frequency of Ca²⁺ transients, lower amplitude of peak Ca²⁺ transients and lower total Ca²⁺ activity in layer II/III motor cortex neurons. While at resting conditions, only Ca²⁺ frequency was increased. Brain levels of soluble pathological tau correlated better than insoluble tau levels with the degree of Ca²⁺ dysfunction in tauopathy mice. Furthermore, tau monoclonal antibody 4E6 partially rescued Ca²⁺ activity abnormalities in tauopathy mice after two intravenous injections and decreased soluble pathological tau protein within the brain. This correlation and antibody effects strongly suggest that the neuronal Ca²⁺ dyshomeostasis is causally linked to pathological tau protein. These findings also reveal more pronounced neuronal Ca²⁺ dysregulation in tauopathy mice than previously reported by two-photon imaging that can be partially corrected with an acute tau antibody treatment.

Laser scanning plays an important role in a broad range of applications. Toward 3D aberration-free scanning, a remote focusing technique has been developed for high-speed imaging applications. However, the implementation of remote focusing often suffers from a limited axial scan range as a result of unknown aberration. Through simple analysis, we show that the sample-to-image path length conservation is crucially important to the remote focusing performance. To enhance the axial scan range, we propose and demonstrate an image-plane aberration correction method. Using a static correction, we can effectively improve the focus quality over a large defocusing range. Experimentally, we achieved ∼three times greater defocusing range than that of conventional methods. This technique can broadly benefit the implementations of high-speed large-volume 3D imaging.

In many parts of the nervous system, experience-dependent refinement of neuronal circuits predominantly involves synapse elimination. The role of sleep in this process remains unknown. We investigated the role of sleep in experience-dependent dendritic spine elimination of layer 5 pyramidal neurons in the visual (V1) and frontal association cortex (FrA) of 1-month-old mice. We found that monocular deprivation (MD) or auditory-cued fear conditioning (FC) caused rapid spine elimination in V1 or FrA, respectively. MD- or FC-induced spine elimination was significantly reduced after total sleep or REM sleep deprivation. Total sleep or REM sleep deprivation also prevented MD- and FC-induced reduction of neuronal activity in response to visual or conditioned auditory stimuli. Furthermore, dendritic calcium spikes increased substantially during REM sleep, and the blockade of these calcium spikes prevented MD- and FC-induced spine elimination. These findings reveal an important role of REM sleep in experience-dependent synapse elimination and neuronal activity reduction.

Phosphorescence lifetime measurement holds great importance in life sciences and material sciences. Due to the long lifetime of phosphorescence emission, conventional approaches based on point scanning time-domain recording suffer from long recording time and low signal-to-noise ratio (SNR). To overcome these difficulties, we developed a line scanning mechanical streak camera for parallel and high SNR imaging. This design offers three key advantages. First, hundreds to thousands of pixels can be recorded simultaneously at high throughput. Second, hundreds of excitation can be accumulated on a single camera frame and read out at once with high quantum efficiency (QE) and low read noise. Third, the system is very simple, only requiring a camera and a scanner. Using a confocal line scanning configuration, we imaged samples of various lifetime ranging from tens of nanoseconds to hundreds of microseconds, which demonstrated the versatility and advantages of this method.

Laser scanning has been widely used in material processing and optical imaging. Among the established scanners, resonant galvo scanners offer high scanning throughput and 100% duty cycle and have been employed in various laser scanning microscopes. However, the common applications of resonant galvo often suffer from position jitters which could introduce substantial measurement artifacts. In this work, we systematically quantify the impact of position sensor, data acquisition system and air turbulence and provide a simple solution to achieve jitter free high-throughput measurement.

Laser scanning is widely employed in imaging and material processing. Common laser scanners are often fast for 2D transverse scanning. Rapid focal depth control is highly desired in many applications. Although remote focusing has been developed to achieve fast focal depth control, the implementation is limited by the laser damage to the actuator near laser focus. Here, we present a new method named pupil plane actuated remote focusing, which enables sub-millisecond response time while avoiding laser damage. We demonstrate its application by implementing a dual-plane two-photon laser scanning fluorescence microscope for in vivo recording of calcium transient of neurons in mouse neocortex.

Large-scale fluorescence calcium imaging methods have become widely adopted for studies of long-term hippocampal and cortical neuronal dynamics. Pyramidal neurons of the rodent hippocampus show spatial tuning in freely foraging or head-fixed navigation tasks. Development of efficient neural decoding methods for reconstructing the animal's position in real or virtual environments can provide a fast readout of spatial representations in closed-loop neuroscience experiments. Here, we develop an efficient strategy to extract features from fluorescence calcium imaging traces and further decode the animal's position. We validate our spike inference-free decoding methods in multiple in vivo calcium imaging recordings of the mouse hippocampus based on both supervised and unsupervised decoding analyses. We systematically investigate the decoding performance of our proposed methods with respect to the number of neurons, imaging frame rate, and signal-to-noise ratio. Our proposed supervised decoding analysis is ultrafast and robust, and thereby appealing for real-time position decoding applications based on calcium imaging.

Wide field fluorescence microscopy is the most commonly employed fluorescence imaging modality. However, a major drawback of wide field imaging is the very limited imaging depth in scattering samples. By experimentally varying the control of illumination, we found that the optimized illumination profile can lead to large contrast improvement for imaging at a depth beyond four scattering path lengths. At such imaging depth, we found that the achieved image signal-to-noise ratio can rival that of confocal measurement. As the employed illumination control is very simple, the method can be broadly applied to a wide variety of wide field fluorescence imaging systems.