Evaluation of Nanoparticle Uptake in Tumors in Real Time Using Intravital Imaging

Current technologies for tumor imaging, such as ultrasound, MRI, PET and CT, are unable to yield high-resolution images for the assessment of nanoparticle uptake in tumors at the microscopic level^1,2,3, highlighting the utility of a suitable xenograft model in which to perform detailed uptake analyses. Here, we use high-resolution intravital imaging to evaluate nanoparticle uptake in human tumor xenografts in a modified, shell-less chicken embryo model. The chicken embryo model is particularly well-suited for these in vivo analyses because it supports the growth of human tumors, is relatively inexpensive and does not require anesthetization or surgery 4,5. Tumor cells form fully vascularized xenografts within 7 days when implanted into the chorioallantoic membrane (CAM) ⁶. The resulting tumors are visualized by non-invasive real-time, high-resolution imaging that can be maintained for up to 72 hours with little impact on either the host or tumor systems. Nanoparticles with a wide range of sizes and formulations administered distal to the tumor can be visualized and quantified as they flow through the bloodstream, extravasate from leaky tumor vasculature, and accumulate at the tumor site. We describe here the analysis of nanoparticles derived from Cowpea mosaic virus (CPMV) decorated with near-infrared fluorescent dyes and/or polyethylene glycol polymers (PEG) ^{7, 8, 9,10,11}. Upon intravenous administration, these viral nanoparticles are rapidly internalized by endothelial cells, resulting in global labeling of the vasculature both outside and within the tumor^7,12. PEGylation of the viral nanoparticles increases their plasma half-life, extends their time in the circulation, and ultimately enhances their accumulation in tumors via the enhanced permeability and retention (EPR) effect ^{7, 10,11}. The rate and extent of accumulation of nanoparticles in a tumor is measured over time using image analysis software. This technique provides a method to both visualize and quantify nanoparticle dynamics in human tumors.     

采用活体成像技术监测肿瘤生长及转移模型的建立

目的采用活体成像技术监测稳定高表达荧光素酶报告基因的肿瘤细胞在小鼠体内生长及转移情况,为肿瘤治疗的药物研发提供新的有用工具。方法采用lipofectamine2000介导的基因转染方法,将pcDNA3．1 7Luc载体转染小鼠高转移乳腺癌细胞株4T1、EMT-6及结肠癌细胞株CT26,经G418抗性筛选及有限稀释法获得可稳定高表达荧光素酶的单克隆细胞;MTT法测定各转染细胞对不同化疗药物的抗性,并采用活体成像的方法检测各转染细胞在小鼠体内的成瘤和转移。结果获得了可稳定高表达荧光素酶基因的单克隆细胞株,该单克隆细胞株具有与亲本细胞系相同的对化疗药物的敏感性;将单克隆细胞株植入小鼠皮下,可采用活体成像技术准确监测肿瘤细胞体内生长及转移。结论采用活体成像技术构建的肿瘤动物模型是拓展肿瘤体内生长、转移及治疗相关研究的理想模型。     

Intravital Imaging of the Mouse Popliteal Lymph Node

Lymph nodes (LNs) are secondary lymphoid organs, which are strategically located throughout the body to allow for trapping and presentation of foreign antigens from peripheral tissues to prime the adaptive immune response. Juxtaposed between innate and adaptive immune responses, the LN is an ideal site to study immune cell interactions^1,2. Lymphocytes (T cells, B cells and NK cells), dendritic cells (DCs), and macrophages comprise the bulk of bone marrow-derived cellular elements of the LN. These cells are strategically positioned in the LN to allow efficient surveillance of self antigens and potential foreign antigens^3-5. The process by which lymphocytes successfully encounter cognate antigens is a subject of intense investigation in recent years, and involves an integration of molecular contacts including antigen receptors, adhesion molecules, chemokines, and stromal structures such as the fibro-reticular network^2,6-12. Prior to the development of high-resolution real-time fluorescent in vivo imaging, investigators relied on static imaging, which only offers answers regarding morphology, position, and architecture. While these questions are fundamental in our understanding of immune cell behavior, the limitations intrinsic with this technique does not permit analysis to decipher lymphocyte trafficking and environmental clues that affect dynamic cell behavior. Recently, the development of intravital two-photon laser scanning microscopy (2P-LSM) has allowed investigators to view the dynamic movements and interactions of individual cells within live LNs in situ^12-16. In particular, we and others have applied this technique to image cellular behavior and interactions within the popliteal LN, where its compact, dense nature offers the advantage of multiplex data acquisition over a large tissue area with diverse tissue sub-structures^11,17-18. It is important to note that this technique offers added benefits over explanted tissue imaging techniques, which require disruption of blood, lymph flow, and ultimately the cellular dynamics of the system. Additionally, explanted tissues have a very limited window of time in which the tissue remains viable for imaging after explant. With proper hydration and monitoring of the animal''s environmental conditions, the imaging time can be significantly extended with this intravital technique. Here, we present a detailed method of preparing mouse popliteal LN for the purpose of performing intravital imaging.     

A Novel Model of IgE-Mediated Passive Pulmonary Anaphylaxis in Rats

Mast cells are central effector cells in allergic asthma and are augmented in the airways of asthma patients. Attenuating mast cell degranulation and with it the early asthmatic response is an important intervention point to inhibit bronchoconstriction, plasma exudation and tissue oedema formation. To validate the efficacy of novel pharmacological interventions, appropriate and practicable in vivo models reflecting mast cell-dependent mechanisms in the lung, are missing. Thus, we developed a novel model of passive pulmonary anaphylaxis in rats. Rats were passively sensitized by concurrent intratracheal and intradermal (ear) application of an anti-DNP IgE antibody. Intravenous application of the antigen, DNP-BSA in combination with Evans blue dye, led to mast cell degranulation in both tissues. Quantification of mast cell degranulation in the lung was determined by (1) mediator release into bronchoalveolar lavage, (2) extravasation of Evans blue dye into tracheal and bronchial lung tissue and (3) invasive measurement of antigen-induced bronchoconstriction. Quantification of mast cell degranulation in the ear was determined by extravasation of Evans blue dye into ear tissue. We pharmacologically validated our model using the SYK inhibitor Fostamatinib, the H₁-receptor antagonist Desloratadine, the mast cell stabilizer disodium cromoglycate (DSCG) and the β₂-adrenergic receptor agonist Formoterol. Fostamatinib was equally efficacious in lung and ear. Desloratadine effectively inhibited bronchoconstriction and ear vascular leakage, but was less effective against pulmonary vascular leakage, perhaps reflecting the differing roles for histamine receptor sub-types. DSCG attenuated both vascular leakage in the lung and bronchoconstriction, but with a very short duration of action. As an inhaled approach, Formoterol was more effective in the lung than in the ear. This model of passive pulmonary anaphylaxis provides a tissue relevant readout of early mast cell activity and pharmacological benchmarking broadly reflects responses observed in patients with asthma.     

A Novel Mouse Model of Soft-Tissue Infection Using Bioluminescence Imaging Allows Noninvasive,Real-Time Monitoring of Bacterial Growth

Musculoskeletal infections, including surgical-site and implant-associated infections, often cause progressive inflammation and destroy areas of the soft tissue. Treating infections, especially those caused by multi-antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) remains a challenge. Although there are a few animal models that enable the quantitative evaluation of infection in soft tissues, these models are not always reproducible or sustainable. Here, we successfully established a real-time, in vivo, quantitative mouse model of soft-tissue infection in the superficial gluteus muscle (SGM) using bioluminescence imaging. A bioluminescent strain of MRSA was inoculated into the SGM of BALB/c adult male mice, followed by sequential measurement of bacterial photon intensity and serological and histological analyses of the mice. The mean photon intensity in the mice peaked immediately after inoculation and remained stable until day 28. The serum levels of interleukin-6, interleukin-1 and C-reactive protein at 12 hours after inoculation were significantly higher than those prior to inoculation, and the C-reactive protein remained significantly elevated until day 21. Histological analyses showed marked neutrophil infiltration and abscesses containing necrotic and fibrous tissues in the SGM. With this SGM mouse model, we successfully visualized and quantified stable bacterial growth over an extended period of time with bioluminescence imaging, which allowed us to monitor the process of infection without euthanizing the experimental animals. This model is applicable to in vivo evaluations of the long-term efficacy of novel antibiotics or antibacterial implants.     

A Novel Model of Mild Traumatic Brain Injury for Juvenile Rats

Despite growing evidence that childhood represents a major risk period for mild traumatic brain injury (mTBI) from sports-related concussions, motor vehicle accidents, and falls, a reliable animal model of mTBI had previously not been developed for this important aspect of development. The modified weight-drop technique employs a glancing impact to the head of a freely moving rodent transmitting acceleration, deceleration, and rotational forces upon the brain. When applied to juvenile rats, this modified weight-drop technique induced clinically relevant behavioural outcomes that were representative of post-concussion symptomology. The technique is a rapidly applied procedure with an extremely low mortality rate, rendering it ideal for high-throughput studies of therapeutics. In addition, because the procedure involves a mild injury to a closed head, it can easily be used for studies of repetitive brain injury. Owing to the simplistic nature of this technique, and the clinically relevant biomechanics of the injury pathophysiology, the modified weight-drop technique provides researchers with a reliable model of mTBI that can be used in a wide variety of behavioural, molecular, and genetic studies.     

Fat Preference: A Novel Model of Eating Behavior in Rats

Obesity is a growing problem in the United States of America, with more than a third of the population classified as obese. One factor contributing to this multifactorial disorder is the consumption of a high fat diet, a behavior that has been shown to increase both caloric intake and body fat content. However, the elements regulating preference for high fat food over other foods remain understudied.To overcome this deficit, a model to quickly and easily test changes in the preference for dietary fat was developed. The Fat Preference model presents rats with a series of choices between foods with differing fat content. Like humans, rats have a natural bias toward consuming high fat food, making the rat model ideal for translational studies. Changes in preference can be ascribed to the effect of either genetic differences or pharmacological interventions. This model allows for the exploration of determinates of fat preference and screening pharmacotherapeutic agents that influence acquisition of obesity.     

Functional Imaging of Rel Expression in Inflammatory Processes Using Bioluminescence Imaging System in Transgenic Mice

c-Rel plays important roles in many inflammatory diseases. Revealing the dynamic expression of c-Rel in disease processes in vivo is critical for understanding c-Rel functions and for developing anti-inflammatory drugs. In this paper, a transgenic mouse line, B6-Tg(c-Rel-luc)^Mlit, which incorporated the transgene firefly luciferase driven by a 14.5-kb fragment containing mouse c-Rel gene Rel promoter, was generated to monitor Rel expression in vivo. Luciferase expression could be tracked in living mice by the method of bioluminescence imaging in a variety of inflammatory processes, including LPS induced sepsis and EAE disease model. The luciferase expression in transgenic mice was comparable to the endogenous Rel expression and could be suppressed by administration of anti-inflammatory drug dexamethasone or aspirin. These results indicate that the B6-Tg(c-Rel-luc)^Mlit mouse is a valuable animal model to study Rel expression in physiological and pathological processes, and the effects of various drug treatments in vivo.     

Promotion of Endodontic Lesions in Rats by a Novel Extraradicular Biofilm Model Using Obturation Materials

Although extraradicular biofilm formation is related to refractory periapical periodontitis, the mechanism of extraradicular biofilm development, as well as its effect on periapical lesions, is unknown. Therefore, we aimed to develop an in vivo extraradicular biofilm model in rats and to identify and quantify extraradicular biofilm-forming bacteria while investigating the effect of extraradicular biofilms on periapical lesions. Periapical lesions were induced by exposing the pulpal tissue of the mandibular first molars of male Wistar rats to their oral environment. Four weeks later, gutta-percha points were excessively inserted into the mesial root canals of the right first molars (experimental sites) but not the left first molars (control sites). After 6 and 8 weeks of pulp exposure, the presence of extraradicular biofilms was confirmed histomorphologically, and biofilm-forming bacteria were identified by using classical culture methods. The biofilms were observed in the extraradicular area of the experimental sites. Similar species were detected both inside and outside the root canals. The bacterial count, quantified by real-time PCR assays, in the extraradicular area gradually increased in the experimental sites until 20 weeks after pulp exposure. After 8 weeks of pulp exposure, the periapical lesion volume that was measured by micro-computed tomography was significantly larger in the experimental sites than in the control sites (P < 0.05 by Welch''s t test). These results suggest that we developed an extraradicular biofilm model in rats and that extraradicular biofilms affect developing periapical lesions.     

A Novel GBM Saliency Detection Model Using Multi-Channel MRI

The automatic computerized detection of regions of interest (ROI) is an important step in the process of medical image processing and analysis. The reasons are many, and include an increasing amount of available medical imaging data, existence of inter-observer and inter-scanner variability, and to improve the accuracy in automatic detection in order to assist doctors in diagnosing faster and on time. A novel algorithm, based on visual saliency, is developed here for the identification of tumor regions from MR images of the brain. The GBM saliency detection model is designed by taking cue from the concept of visual saliency in natural scenes. A visually salient region is typically rare in an image, and contains highly discriminating information, with attention getting immediately focused upon it. Although color is typically considered as the most important feature in a bottom-up saliency detection model, we circumvent this issue in the inherently gray scale MR framework. We develop a novel pseudo-coloring scheme, based on the three MRI sequences, viz. FLAIR, T2 and T1C (contrast enhanced with Gadolinium). A bottom-up strategy, based on a new pseudo-color distance and spatial distance between image patches, is defined for highlighting the salient regions in the image. This multi-channel representation of the image and saliency detection model help in automatically and quickly isolating the tumor region, for subsequent delineation, as is necessary in medical diagnosis. The effectiveness of the proposed model is evaluated on MRI of 80 subjects from the BRATS database in terms of the saliency map values. Using ground truth of the tumor regions for both high- and low- grade gliomas, the results are compared with four highly referred saliency detection models from literature. In all cases the AUC scores from the ROC analysis are found to be more than 0.999 ± 0.001 over different tumor grades, sizes and positions.     

激肽释放酶转基因大鼠模型的建立

目的建立KLK1转基因大鼠模型。方法腹腔注射PMSG-HCG（150-150IU/kg）超排不同周龄（4-8周）SD大鼠比较超排效果的差异,以可用于注射胚胎数作为评判标准确定最佳超排周龄。构建pBC-klk1转基因构件,经酶切、纯化后通过显微注射方法导入SD大鼠受精卵原核并移植到同期受孕的SD受体母鼠输卵管内。出生后仔鼠用PCR和Southern方法检测鼠尾DNA鉴定基因型,通过RT-PCR和免疫组化方法检测klk1基因表达。结果4-8周SD大鼠超排后分别获得受精卵14±14.8、30±15.2、13.3±13.7、13±14.7、8±5.7,5周龄大鼠超排效果最好,与其他周龄大鼠相比有显差异,P〈0.05;显微注射1538枚卵,移植685（44.53%）枚卵于31只受体输卵管中,12（12/31,38.7%）只怀孕,共产仔62只,经PCR检测获得6只阳性鼠,Southern检测3只阳性。对Southern检测阳性转基因大鼠子代进行RT-PCR检测和免疫组化分析证明klk1基因在肾脏、胰腺和乳腺内表达。结论成功建立klk1基因表达的转基因大鼠模型,该模型是高血压病研究的理想动物模型。     

Differential Susceptibility of SD and CD Rats to a Novel Rat Theilovirus

Antibodies to rat theilovirus (RTV) have been detected in rats for many years because of their serologic crossreactivity with strains of Theiler murine encephalomyelitis virus (TMEV) of mice. Little information exists regarding this pathogen, yet it is among the most common viruses detected in serologic surveys of rats used in research. In the study reported here, a novel isolate of RTV, designated RTV1, was cultured from the feces of infected rats. The RTV1 genome contained 8094 nucleotides and had approximately 95% identity with another rat theilovirus, NSG910, and 73% identity with TMEV strains. In addition, the genome size of RTV1 was similar to those of TMEV strains but larger than that reported for NSG910. Oral inoculation of Sprague–Dawley (SD) and CD male rats (n = 10 each group) with RTV1 revealed that SD rats were more susceptible than CD rats to RTV1 infection. At 14 d postinoculation, 100% of SD rats shed virus in the feces, and 70% were positive for RTV serum antibodies. By 56 d postinoculation 30% of SD rats continued to have detectable virus in the feces, and 90% had seroconverted. In contrast, in inoculated CD rats RTV was detected only in the feces at 14 d postinoculation, at which time 40% of CD rats were fecal positive. By 56 d postinoculation only 20% of CD rats had detectable RTV serum antibodies. Our data provide additional sequence information regarding a rat-specific Cardiovirus and indicate that SD rats are more susceptible than CD rats to RTV1 infection.Abbreviations: RACE, rapid amplification of cDNA ends; RTV, rat theilovirus; SD, Sprague Dawley; TMEV, Theiler murine encephalomyelitis virusFor decades it has been known that rats used in research can develop antibodies to a Cardiovirus that is antigenically similar to Theiler murine encephalomyelitis virus (TMEV) of mice.^{4,6,10,12,13,20} Recent reports on the prevalence of antibodies in rats to this Cardiovirus vary from approximately 0.6% of sera tested from research rats in North America¹⁰ to 54.4% in a survey of 18 Brazilian research facilities.^3,6,20 Multiple designations have been used to identify the Cardiovirus that infects rats, including Theiler-like virus of rats,¹³ Theiler murine encephalomyelitis virus (TMEV),²⁰ rat enterovirus,¹ rat encephalomyelitis virus,⁷ rat cardiovirus,¹⁵ and recently rat theilovirus.² We have elected to refer to the virus as rat theilovirus (RTV), consistent with 1 of the cited references,² to indicate the relation of the rat virus to TMEV of mice and to identify it as a rat-specific agent.The first report of natural infection of rats with a Cardiovirus was in 1964 with the discovery of MHG virus.¹² The finding resulted from an isolated observation in which a few rats in a large research colony displayed clinical signs indicative of central nervous system deficits, including incoordination, torticollis, circling, and tremors. The MHG virus recovered from infected rats was antigenically crossreactive with TMEV strain GDVII and had physical properties consistent with viruses in the Picornaviridae family. The virus was propagated in cell culture, and neurologic disease was reproduced when virus was inoculated into suckling mice and suckling rats.¹² Subsequent serologic studies using crossneutralization, complement fixation, and hemagglutination inhibition assays further substantiated the antigenic relatedness between MHG virus and multiple strains of TMEV.^4,11 In addition, sera from ‘normal’ rats contained antibodies to the newly identified Theiler-like virus of rats, suggesting widespread infection of the virus in research rat colonies.¹² More recently in Japan, a Theiler-like virus was isolated after intracranial inoculation of newborn Wistar rats with intestinal homogenates from TMEV GDVII-seropositive rats.¹³ Inoculated rats did not develop clinical signs of infection, but virus was cultivated in BHK21 cells from brain homogenates of the 10-d-old Wistar rats inoculated intracranially. Physiochemical properties of the virus, designated NSG910, were consistent with those of the Cardiovirus genus. Sequence analysis also showed that NSG910 was a Cardiovirus in the family Picornaviridae that was related to, but distinct from MHG virus, and strains of TMEV. This report served to further document the existence of a unique Cardiovirus of rats closely related to, but distinct from, TMEV strains.¹³ In a recent report from Brazil, neonatal mice and rats inoculated with intestinal homogenates from rats with antibodies to TMEV strain GDVII developed neurologic signs of flaccid hindlimb paralysis and tremors. In addition, brain homogenates from the affected animals were positive by RT-PCR for cardioviral RNA.²⁰Picornavirus virions are approximately 30 nm in diameter, nonenveloped, with icosahedral symmetry and a single-stranded, positive-sense RNA genome.¹⁹ Encephalomyocarditis virus and Theilovirus are 2 species of Cardiovirus in the Picornaviridae family. Encephalomyocarditis virus species includes mengovirus, Maus Elberfeld virus, and Columbia SK virus.⁷ Strains of Theilovirus species include TMEV, Vilyuisk virus, and RTV.^13,18,22 Most often studied are the TMEV strains, which are classified according to their neurovirulence after intracerebral inoculation. Included are the highly neurovirulent GD VII and FA strains²³ and the less virulent, more persistent DA, BeAn 8386, WW, and TO (Theiler original) strains.^9,17,22 Studies have shown that the virus replicates in the alimentary tract and is shed in the feces of infected mice.^15,19 Mice rarely show clinical disease when infected under natural conditions; however, neurologic manifestations have been reported.^21,24Sentinel animals typically are used to survey rodent colonies for the presence or absence of infectious agents. Outbred stocks are frequently used as sentinels because of their vigor, relatively low cost, and ability to mount a robust humoral immune response to infectious agents.^8,14 Sprague–Dawley (SD) and CD rats are 2 stocks that are commonly used as sentinels for rat colonies. The origins of the SD rat (Rattus norvegicus) date back to the 1920s as a result of mating Wistar stock with a hybrid rat stock of unknown origin. In the 1950s, an SD breeding stock was cesarean derived in an effort to improve microbiologic status. This nucleus of cesarean-derived rats formed the foundation of the CD rat stock.²⁵ Because SD and CD rat stocks have a common ancestry, they frequently are considered to be interchangeable for the purpose of sentinel animals.In the studies reported here, we isolated and propagated a novel strain of Theilovirus, referred to as RTV1, from the feces of infected SD rats. The entire genome of RTV1 was sequenced and compared with those of isolates of TMEV and NSG910, the only other isolate of RTV to be sequenced in its entirety. In addition, we evaluated the susceptibility of SD and CD outbred rats to RTV1 after oral inoculation with the virus.     

Microscopic Delineation of Medulloblastoma Margins in a Transgenic Mouse Model Using a Topically Applied VEGFR-1 Probe

The unambiguous demarcation of tumor margins is critical at the final stages in the surgical treatment of brain tumors because patient outcomes have been shown to correlate with the extent of resection. Real-time high-resolution imaging with the aid of a tumor-targeting fluorescent contrast agent has the potential to enable intraoperative differentiation of tumor versus normal tissues with accuracy approaching the current gold standard of histopathology. In this study, a monoclonal antibody targeting the vascular endothelial growth factor receptor 1 (VEGFR-1) was conjugated to fluorophores and evaluated as a tumor contrast agent in a transgenic mouse model of medulloblastoma. The probe was administered topically, and its efficacy as an imaging agent was evaluated in vitro using flow cytometry, as well as ex vivo on fixed and fresh tissues through immunohistochemistry and dual-axis confocal microscopy, respectively. Results show a preferential binding to tumor versus normal tissue, suggesting that a topically applied VEGFR-1 probe can potentially be used with real-time intraoperative optical sectioning microscopy to guide brain tumor resections.     

潮霉素抗性转基因BDF1小鼠模型的建立

目的建立具有潮霉素（hygromycin）抗性转基因BDF1小鼠,用于制备携有hygromycin抗性筛选标志ES阳性细胞克隆的饲养层。方法通过显微注射的方法,将含有潮霉素B磷酸转移酶基因片段（5.1kb）导入BDF1受精卵雄原核中,共注射169枚受精卵,然后将129枚受精卵细胞植入同期受孕的受体母鼠输卵管内。结果共产生37只转基因小鼠,经PCR和Southern检测获得9只阳性小鼠,对一只子代鼠进行RT-PCR检测证明hyg基因已经在肾、肌肉、脾内表达。结论成功的建立具有潮霉素抗性的BDF1转基因鼠,该模型动物可以为基因敲除研究提供良好的基础条件。     

A Novel Procedure for Rapid Imaging of Adult Mouse Brains with MicroCT Using Iodine-Based Contrast

High-resolution Magnetic Resonance Imaging (MRI) has been the primary modality for obtaining 3D cross-sectional anatomical information in animals for soft tissue, particularly brain. However, costs associated with MRI can be considerably high for large phenotypic screens for gross differences in the structure of the brain due to pathology and/or experimental manipulations. MicroCT (mCT), especially benchtop mCT, is becoming a common laboratory equipment with throughput rates equal or faster than any form of high-resolution MRI at lower costs. Here we explore adapting previously developed contrast based mCT to image adult mouse brains in-situ. We show that 2% weight per volume (w/v) iodine-potassium iodide solution can be successfully used to image adult mouse brains within 48 hours post-mortem when a structural support matrix is used. We demonstrate that hydrogel can be effectively used as a perfusant which limits the tissue shrinkage due to iodine.     

A Novel Application of Musculoskeletal Ultrasound Imaging

Ultrasound is an attractive modality for imaging muscle and tendon motion during dynamic tasks and can provide a complementary methodological approach for biomechanical studies in a clinical or laboratory setting. Towards this goal, methods for quantification of muscle kinematics from ultrasound imagery are being developed based on image processing. The temporal resolution of these methods is typically not sufficient for highly dynamic tasks, such as drop-landing. We propose a new approach that utilizes a Doppler method for quantifying muscle kinematics. We have developed a novel vector tissue Doppler imaging (vTDI) technique that can be used to measure musculoskeletal contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities using ultrasound. The goal of this preliminary study was to investigate the repeatability and potential applicability of the vTDI technique in measuring musculoskeletal velocities during a drop-landing task, in healthy subjects. The vTDI measurements can be performed concurrently with other biomechanical techniques, such as 3D motion capture for joint kinematics and kinetics, electromyography for timing of muscle activation and force plates for ground reaction force. Integration of these complementary techniques could lead to a better understanding of dynamic muscle function and dysfunction underlying the pathogenesis and pathophysiology of musculoskeletal disorders.     

Characterization of Gastric and Neuronal Histaminergic Populations Using a Transgenic Mouse Model

Histamine is a potent biogenic amine that mediates numerous physiological processes throughout the body, including digestion, sleep, and immunity. It is synthesized by gastric enterochromaffin-like cells, a specific set of hypothalamic neurons, as well as a subset of white blood cells, including mast cells. Much remains to be learned about these varied histamine-producing cell populations. Here, we report the validation of a transgenic mouse line in which Cre recombinase expression has been targeted to cells expressing histidine decarboxylase (HDC), which catalyzes the rate-limiting step in the synthesis of histamine. This was achieved by crossing the HDC-Cre mouse line with Rosa26-tdTomato reporter mice, thus resulting in the expression of the fluorescent Tomato (Tmt) signal in cells containing Cre recombinase activity. As expected, the Tmt signal co-localized with HDC-immunoreactivity within the gastric mucosa and gastric submucosa and also within the tuberomamillary nucleus of the brain. HDC expression within Tmt-positive gastric cells was further confirmed by quantitative PCR analysis of mRNA isolated from highly purified populations of Tmt-positive cells obtained by fluorescent activated cell sorting (FACS). HDC expression within these FACS-separated cells was found to coincide with other markers of both ECL cells and mast cells. Gastrin expression was co-localized with HDC expression in a subset of histaminergic gastric mucosal cells. We suggest that these transgenic mice will facilitate future studies aimed at investigating the function of histamine-producing cells.     

Physiological Characterization of Vestibular Efferent Brainstem Neurons Using a Transgenic Mouse Model

The functional role of efferent innervation of the vestibular end-organs in the inner ear remains elusive. This study provides the first physiological characterization of the cholinergic vestibular efferent (VE) neurons in the brainstem by utilizing a transgenic mouse model, expressing eGFP under a choline-acetyltransferase (ChAT)-locus spanning promoter in combination with targeted patch clamp recordings. The intrinsic electrical properties of the eGFP-positive VE neurons were compared to the properties of the lateral olivocochlear (LOC) brainstem neurons, which gives rise to efferent innervation of the cochlea. Both VE and the LOC neurons were marked by their negative resting membrane potential <−75 mV and their passive responses in the hyperpolarizing range. In contrast, the response properties of VE and LOC neurons differed significantly in the depolarizing range. When injected with positive currents, VE neurons fired action potentials faithfully to the onset of depolarization followed by sparse firing with long inter-spike intervals. This response gave rise to a low response gain. The LOC neurons, conversely, responded with a characteristic delayed tonic firing upon depolarizing stimuli, giving rise to higher response gain than the VE neurons. Depolarization triggered large TEA insensitive outward currents with fast inactivation kinetics, indicating A-type potassium currents, in both the inner ear-projecting neuronal types. Immunohistochemistry confirmed expression of Kv4.3 and 4.2 ion channel subunits in both the VE and LOC neurons. The difference in spiking responses to depolarization is related to a two-fold impact of these transient outward currents on somatic integration in the LOC neurons compared to in VE neurons. It is speculated that the physiological properties of the VE neurons might be compatible with a wide-spread control over motion and gravity sensation in the inner ear, providing likewise feed-back amplification of abrupt and strong phasic signals from the semi-circular canals and of tonic signals from the gravito-sensitive macular organs.     

A Distinct Smoothened Mutation Causes Severe Cerebellar Developmental Defects and Medulloblastoma in a Novel Transgenic Mouse Model

Deregulated developmental processes in the cerebellum cause medulloblastoma, the most common pediatric brain malignancy. About 25 to 30% of cases are caused by mutations increasing the activity of the Sonic hedgehog (Shh) pathway, a critical mitogen in cerebellar development. The proto-oncogene Smoothened (Smo) is a key transducer of the Shh pathway. Activating mutations in Smo that lead to constitutive activity of the Shh pathway have been identified in human medulloblastoma. To understand the developmental and oncogenic effects of two closely positioned point mutations in Smo, we characterized NeuroD2-SmoA2 mice and compared them to NeuroD2-SmoA1 mice. While both SmoA1 and SmoA2 transgenes cause medulloblastoma with similar frequencies and timing, SmoA2 mice have severe aberrations in cerebellar development, whereas SmoA1 mice are largely normal during development. Intriguingly, neurologic function, as measured by specific tests, is normal in the SmoA2 mice despite extensive cerebellar dysplasia. We demonstrate how two nearly contiguous point mutations in the same domain of the encoded Smo protein can produce striking phenotypic differences in cerebellar development and organization in mice.     

Investigation of Oncogenic Cooperation in Simple Liver-Specific Transgenic Mouse Models Using Noninvasive In Vivo Imaging

Liver cancer is a complex multistep process requiring genetic alterations in multiple proto-oncogenes and tumor suppressor genes. Although hundreds of genes are known to play roles in hepatocarcinogenesis, oncogenic collaboration among these genes is still largely unknown. Here, we report a simple methodology by which oncogenic cooperation between cancer-related genes can be efficiently investigated in the liver. We developed various non-germline transgenic mouse models using hydrodynamics-based transfection which express HrasG12V, SmoM2, and a short-hairpin RNA down-regulating p53 (shp53) individually or in combination in the liver. In this transgenic system, firefly luciferase was co-expressed with the oncogenes as a reporter, allowing tumor growth in the liver to be monitored over time without an invasive procedure. Very strong bioluminescence imaging (BLI) signals were observed at 4 weeks post-hydrodynamic injection (PHI) in mice co-expressing HrasG12V and shp53, while only background signals were detected in other double or single transgenic groups until 30 weeks PHI. Consistent with the BLI data, tumors were observed in the HrasG12V plus shp53 group at 4 weeks PHI, while other transgenic groups failed to exhibit a hyperplastic nodule at 30 weeks PHI. In the HrasG12V plus shp53 transgenic group, BLI signals were well-correlated with actual tumor growth in the liver, confirming the versatility of BLI-based monitoring of tumor growth in this organ. The methodology described here is expected to accelerate and facilitate in vivo studies of the hepatocarcinogenic potential of cancer-related genes by means of oncogenic cooperation.