Osteoporosis is a major public health problem worldwide. Here, we present a quantitative multispectral photoacoustic method for the evaluation of bone pathologies which has significant advantages over pure ultrasonic or pure optical methods as it provides both molecular information and bone mechanical status. This is enabled via a simultaneous measurement of the bone's optical properties as well as the speed of sound and ultrasonic attenuation in the bone. To test the method's quantitative predictions, a combined ultrasonic and photoacoustic system was developed. Excitation was performed optically via a portable triple laser‐diode system and acoustically via a single element transducer. Additional dual transducers were used for detecting the acoustic waves that were generated by the two modalities. Both temporal and spectral parameters were compared between different excitation wavelengths and measurement modalities. Short photoacoustic excitation wavelengths allowed sensing of the cortical layer while longer wavelengths produced results which were compatible with the quantitative ultrasound measurements.
How can adverse experiences in early life, such as maltreatment, exert such powerful negative effects on health decades later? The answer may lie in changes to DNA. New research suggests that exposure to stress can accelerate the erosion of DNA segments called telomeres. Shorter telomere length correlates with chronological age and also disease morbidity and mortality. Thus, telomere erosion is a potential mechanism linking childhood stress to health problems later in life. However, an array of mechanistic, methodological, and basic biological questions must be addressed in order to translate telomere discoveries into clinical applications for monitoring health and predicting disease risk. This paper covers the current state of the science and lays out new research directions. 相似文献
The visual system must make predictions to compensate for inherent delays in its processing. Yet little is known, mechanistically, about how prediction aids natural behaviors. Here, we show that despite a 20-30ms intrinsic processing delay, the vertical motion sensitive (VS) network of the blowfly achieves maximally efficient prediction. This prediction enables the fly to fine-tune its complex, yet brief, evasive flight maneuvers according to its initial ego-rotation at the time of detection of the visual threat. Combining a rich database of behavioral recordings with detailed compartmental modeling of the VS network, we further show that the VS network has axonal gap junctions that are critical for optimal prediction. During evasive maneuvers, a VS subpopulation that directly innervates the neck motor center can convey predictive information about the fly’s future ego-rotation, potentially crucial for ongoing flight control. These results suggest a novel sensory-motor pathway that links sensory prediction to behavior. 相似文献
Synaptic clustering on neuronal dendrites has been hypothesized to play an important role in implementing pattern recognition. Neighboring synapses on a dendritic branch can interact in a synergistic, cooperative manner via nonlinear voltage-dependent mechanisms, such as NMDA receptors. Inspired by the NMDA receptor, the single-branch clusteron learning algorithm takes advantage of location-dependent multiplicative nonlinearities to solve classification tasks by randomly shuffling the locations of “under-performing” synapses on a model dendrite during learning (“structural plasticity”), eventually resulting in synapses with correlated activity being placed next to each other on the dendrite. We propose an alternative model, the gradient clusteron, or G-clusteron, which uses an analytically-derived gradient descent rule where synapses are "attracted to" or "repelled from" each other in an input- and location-dependent manner. We demonstrate the classification ability of this algorithm by testing it on the MNIST handwritten digit dataset and show that, when using a softmax activation function, the accuracy of the G-clusteron on the all-versus-all MNIST task (~85%) approaches that of logistic regression (~93%). In addition to the location update rule, we also derive a learning rule for the synaptic weights of the G-clusteron (“functional plasticity”) and show that a G-clusteron that utilizes the weight update rule can achieve ~89% accuracy on the MNIST task. We also show that a G-clusteron with both the weight and location update rules can learn to solve the XOR problem from arbitrary initial conditions. 相似文献
Chilling temperatures (0–15°C) inhibit photosynthesis in most C4 grasses, yet photosynthesis is chilling tolerant in the ‘Illinois’ clone of the C4 grass Miscanthus x giganteus, a candidate cellulosic bioenergy crop. M. x giganteus is a hybrid between Miscanthus sacchariflorus and Miscanthus sinensis; therefore chilling‐tolerant parent lines might produce hybrids superior to the current clone. Recently a collection of M. sacchariflorus from Siberia, the apparent low temperature limit of natural distribution, became available, which may be a source for chilling tolerance. The collection was screened for chilling tolerance of photosynthesis by measuring dark‐adapted maximum quantum yield of PSII photochemistry (Fv/Fm) on plants in the field in cool weather. Superior accessions were selected for further phenotyping: plants were grown at 25°C, transferred to 10°C (chilling) for 15 days, and returned to 25°C for 7 days (recovery). Two experiments assessed: (a) light‐saturated net photosynthetic rate (Asat) and operating quantum yield of PSII photochemistry (ΦPSII), (b) response of net leaf CO2 uptake (A) to intercellular [CO2] (ci). Three accessions showed superior chilling tolerance: RU2012‐069 and RU2012‐114 achieved Asat up to double that of M. x giganteus prior to and during chilling, due to increased ci ‐ saturated photosynthesis (Vmax). RU2012‐069 and RU2012‐114 also maintained greater levels of ΦPSII during chilling, indicating reduced photodamage. Additionally, accession RU2012‐112 maintained a stable Asat throughout the 15‐day chilling period, while Asat continuously declined in other accessions; this suggests RU2012‐112 could outperform others in lengthy chilling periods. Plants were returned to 25°C after the chilling period; M. x giganteus showed the weakest recovery after 1 day, but a strong recovery after 1 week. This study has therefore identified important genetic resources for the synthesis of improved lines of M. x giganteus, which could facilitate the displacement of fossil fuels by cellulosic bioenergy. 相似文献
The mechanisms controlling wiring of neuronal networks are not completely understood. The stereotypic architecture of the Drosophila mushroom body (MB) offers a unique system to study circuit assembly. The adult medial MB γ‐lobe is comprised of a long bundle of axons that wire with specific modulatory and output neurons in a tiled manner, defining five distinct zones. We found that the immunoglobulin superfamily protein Dpr12 is cell‐autonomously required in γ‐neurons for their developmental regrowth into the distal γ4/5 zones, where both Dpr12 and its interacting protein, DIP‐δ, are enriched. DIP‐δ functions in a subset of dopaminergic neurons that wire with γ‐neurons within the γ4/5 zone. During metamorphosis, these dopaminergic projections arrive to the γ4/5 zone prior to γ‐axons, suggesting that γ‐axons extend through a prepatterned region. Thus, Dpr12/DIP‐δ transneuronal interaction is required for γ4/5 zone formation. Our study sheds light onto molecular and cellular mechanisms underlying circuit formation within subcellular resolution. 相似文献