Dual antithrombotic therapy dose-dependently alters hemostatic plug structure and function

BACKGROUND

Antithrombotic medications carry an inherent risk of bleeding, which may be exacerbated when anticoagulant and antiplatelet therapeutics are combined. Prior studies have shown different effects of antiplatelet vs anticoagulant drugs on the structure and function of hemostatic plugs in vivo.

OBJECTIVES

We examined whether dual antithrombotic treatment consisting of combined antiplatelet and anticoagulant therapeutics alters hemostatic plug structure and function differently from treatment with either therapeutic alone.

METHODS

Mice were treated with the P2Y12 antagonist clopidogrel and the factor Xa inhibitor rivaroxaban across a range of doses, either alone or in combination. The hemostatic response was assessed using a mouse jugular vein puncture injury model. Platelet accumulation and fibrin deposition were evaluated using quantitative multiphoton fluorescence microscopy, and bleeding times were recorded.

RESULTS

Mice treated with clopidogrel alone exhibited a decrease in platelet accumulation at the site of injury, with prolonged bleeding times only at the highest doses of clopidogrel used. Mice treated with rivaroxaban alone instead showed a reduction in fibrin deposition with no impact on bleeding. Mice treated with both clopidogrel and rivaroxaban exhibited platelet and fibrin accumulation that was similar to that with either drug given alone; however, dual antithrombotic therapy resulted in impaired hemostasis at doses that had no impact on bleeding when given in isolation.

CONCLUSION

Combined administration of antiplatelet and anticoagulant therapeutics exacerbates bleeding as compared to that with either drug alone, potentially via combined loss of both adenosine 5'-diphosphate- and thrombin-mediated platelet activation. These findings enhance our understanding of the bleeding risk associated with dual antithrombotic therapy.

Investigation of intact mouse cochleae using two-photon laser scanning microscopy

OBJECTIVES

The investigation of cochlear hair cells and lateral wall is a time-consuming and labor-intensive process. However, it is a mandatory experiment in audiology research. Here we suggest a novel method for investigating the inner ear microstructures from intact cochleae using two-photon laser scanning microscopy (TPLSM). This technique guarantees fewer artifacts and technical simplicity.

METHODS

Using TPLSM, we investigated the whole mount cochleae, decalcified cochleae, and cleared cochleae of wild type C57BL/6 mice. CX3CR1^+/GFP mice were used to investigate the feasibility of visualizing cellular structures in the cochlear spiral ligament. All samples were investigated without staining.

RESULTS

Endogenous fluorescence emission from the outer hair cells was strong enough to be distinguished from the other structures in all samples. From the single apical view, 50 and 90% of the whole hair cells of the decalcified cochleae and cleared cochleae, respectively, could be visualized without staining using TPLSM. Capillary structure of stria vascularis and spiral ligament could be visualized by endogenous fluorescence without staining.

CONCLUSION

We successfully investigated the hair cells and lateral wall of mouse cochleae using TPLSM without using staining or any destructive procedures. This method is easier, faster, and more reliable than conventional methods.

Heterogeneous distribution of doublecortin-expressing cells surrounding the rostral migratory stream in the juvenile mouse

In the postnatal mammalian brain, neural stem cells of the ventricular-subventricular zone continue to generate doublecortin (Dcx)-expressing immature neurons. Throughout life, these immature neurons migrate to the olfactory bulb through the rostral migratory stream (RMS). In this study, we investigated the distribution of these putative immature neurons using enhanced green fluorescent protein (EGFP) expression in the area surrounding the RMS of the juvenile Dcx-EGFP mice. Through the combined use of an optical clearing reagent (a 2,2'-thiodiethanol solution) and two-photon microscopy, we visualized three-dimensionally the EGFP-positive cells in the entire RMS and its surroundings. The resulting wide-field and high-definition images along with computational image processing methods developed in this study were used to comprehensively determine the position of the EGFP-positive cells. Our findings revealed that the EGFP-positive cells were heterogeneously distributed in the area surrounding the RMS. In addition, the orientation patterns of the leading process of these cells, which displayed the morphology of migrating immature neurons, differed depending on their location. These novel results provide highly precise morphological information for immature neurons and suggest that a portion of immature neurons may be detached from the RMS and migrate in various directions.

Fronto-parietal Cortical Circuits Encode Accumulated Evidence with a Diversity of Timescales

Decision-making in dynamic environments often involves accumulation of evidence, in which new information is used to update beliefs and select future actions. Using in vivo cellular resolution imaging in voluntarily head-restrained rats, we examined the responses of neurons in frontal and parietal cortices during a pulse-based accumulation of evidence task. Neurons exhibited activity that predicted the animal's upcoming choice, previous choice, and graded responses that reflected the strength of the accumulated evidence. The pulsatile nature of the stimuli enabled characterization of the responses of neurons to a single quantum (pulse) of evidence. Across the population, individual neurons displayed extensive heterogeneity in the dynamics of responses to pulses. The diversity of responses was sufficiently rich to form a temporal basis for accumulated evidence estimated from a latent variable model. These results suggest that heterogeneous, often transient sensory responses distributed across the fronto-parietal cortex may support working memory on behavioral timescales. VIDEO ABSTRACT.

Fast measurement of sarcomere length and cell orientation in Langendorff-perfused hearts using remote focusing microscopy

RATIONALE

Sarcomere length (SL) is a key indicator of cardiac mechanical function, but current imaging technologies are limited in their ability to unambiguously measure and characterize SL at the cell level in intact, living tissue.

OBJECTIVE

We developed a method for measuring SL and regional cell orientation using remote focusing microscopy, an emerging imaging modality that can capture light from arbitrary oblique planes within a sample.

METHODS AND RESULTS

We present a protocol that unambiguously and quickly determines cell orientation from user-selected areas in a field of view by imaging 2 oblique planes that share a common major axis with the cell. We demonstrate the effectiveness of the technique in establishing single-cell SL in Langendorff-perfused hearts loaded with the membrane dye di-4-ANEPPS.

CONCLUSIONS

Remote focusing microscopy can measure cell orientation in complex 2-photon data sets without capturing full z stacks. The technique allows rapid assessment of SL in healthy and diseased heart experimental preparations.

Coherent anti-stokes Raman scattering (CARS) microscopy: a novel technique for imaging the retina

PURPOSE

To image the cellular and noncellular structures of the retina in an intact mouse eye without the application of exogenous fluorescent labels using noninvasive, nondestructive techniques.

METHODS

Freshly enucleated mouse eyes were imaged using two nonlinear optical techniques: coherent anti-Stokes Raman scattering (CARS) and two-photon autofluorescence (TPAF). Cross sectional transverse sections and sequential flat (en face) sagittal sections were collected from a region of sclera approximately midway between the limbus and optic nerve. Imaging proceeded from the surface of the sclera to a depth of ∼60 μm.

RESULTS

The fluorescent signal from collagen fibers within the sclera was evident in the TPAF channel; the scleral collagen fibers showed no organization and appeared randomly packed. The sclera contained regions lacking TPAF and CARS fluorescence of ∼3 to 15 μm in diameter that could represent small vessels or scleral fibroblasts. Intense punctate CARS signals from the retinal pigment epithelial layer were of a size and shape of retinyl storage esters. Rod outer segments could be identified by the CARS signal from their lipid-rich plasma membranes.

CONCLUSIONS

CARS microscopy can be used to image the outer regions of the mammalian retina without the use of a fluorescent dye or exogenously expressed recombinant protein. With technical advancements, CARS/TPAF may represent a new avenue for noninvasively imaging the retina and might complement modalities currently used in clinical practice.

Integrated multimodal optical microscopy for structural and functional imaging of engineered and natural skin

An integrated multimodal optical microscope is demonstrated for high-resolution, structural and functional imaging of engineered and natural skin. This microscope incorporates multiple imaging modalities including optical coherence (OCM), multi-photon (MPM), and fluorescence lifetime imaging microscopy (FLIM), enabling simultaneous visualization of multiple contrast sources and mechanisms from cells and tissues. Spatially co-registered OCM/MPM/FLIM images of multi-layered skin tissues are obtained, which are formed based on complementary information provided by different modalities, i.e., scattering information from OCM, molecular information from MPM, and functional cellular metabolism states from FLIM. Cellular structures in both the dermis and epidermis, especially different morphological and physiological states of keratinocytes from different epidermal layers, are revealed by mutually-validating images. In vivo imaging of human skin is also investigated, which demonstrates the potential of multimodal microscopy for in vivo investigation during engineered skin engraftment. This integrated imaging technique and microscope show the potential for investigating cellular dynamics in developing engineered skin and following in vivo grafting, which will help refine the control and culturing conditions necessary to obtain more robust and physiologically-relevant engineered skin substitutes.