An experimental rat model for studying pulmonary microcirculation by in vivo videomicroscopy

Multicolor two-photon imaging of in vivo cellular pathophysiology upon influenza virus infection using the two-photon IMPRESS

In vivo two-photon imaging is a valuable technique for studies of viral pathogenesis and host responses to infection in vivo. In this protocol, we describe a methodology for analyzing influenza virus-infected lung in vivo by two-photon imaging microscopy. We describe the surgical procedure, how to stabilize the lung, and an approach to analyzing the data. Further, we provide a database of fluorescent dyes, antibodies, and reporter mouse lines that can be used in combination with a reporter influenza virus (Color-flu) for multicolor analysis. Setup of this model typically takes ~30 min and enables the observation of influenza virus-infected lungs for >4 h during the acute phase of the inflammation and at least 1 h in the lethal phase. This imaging system, which we termed two-photon IMPRESS (imaging pathophysiology research system), is broadly applicable to analyses of other respiratory pathogens and reveals disease progression at the cellular level in vivo.

Intravital microscopy of the lung: minimizing invasiveness

In vivo microscopy has recently become a gold standard in lung immunology studies involving small animals, largely benefiting from the democratization of multiphoton microscopy allowing for deep tissue imaging. This technology represents currently our only way of exploring the lungs and inferring what happens in human respiratory medicine. The interest of lung in vivo microscopy essentially relies upon its relevance as a study model, fulfilling physiological requirements in comparison with in vitro and ex vivo experiments. However, strategies developed in order to overcome movements of the thorax caused by breathing and heartbeats remain the chief drawback of the technique and a major source of invasiveness. In this context, minimizing invasiveness is an unavoidable prerequisite for any improvement of lung in vivo microscopy. This review puts into perspective the main techniques enabling lung in vivo microscopy, providing pros and cons regarding invasiveness.

The cooling tube: A novel small animal model of systemic hypothermia in awake Syrian Golden Hamsters (mesocricetus auratus)

Hypothermia is increasingly used as a therapeutic strategy in a diversity of clinical scenarios. Its impact on mammalian physiology, particularly on the microcirculatory changes of critical organ systems, are, however, incompletely understood. Close examination of the literature reveals a marked paucity of small animal models of rapid systemic hypothermia. All published models introduce important microvascular confounders by investigating either local cooling processes or using anaesthetised animals. Here we present the first rapid systemic hypothermia model in an awake hamster. We developed a waterstream cooled copper tube system for standardized systemic temperature control. With this novel system core body temperature (Tc) in 14 awake animals could be precisely stabilised at temperatures of 30°C and 18°C (7 animals, respectively) within 10-20 min. Rewarming was achieved over 10-15 min. Tolerance of the procedure was excellent. Hamsters did not show any behavioural changes in the mild hypothermia group. In the deep hypothermia group 6 of 7 animals regained normal behaviour within 2-11 hs. As hypothermia was induced in dorsal skinfold chamber bearing animals this model seems suitable for investigation of microcirculatory purposes.Advantages over previously established experimental hypothermia models are significant. Amongst these, the possibility of visualization of microcirculation, the lack of microcirculation confounding factors such as anaesthetic drugs, the ability for precise Tc control and rapid induction of hypothermia are prominent.

Imaging Plasmodium immunobiology in the liver, brain, and lung

Plasmodium falciparum malaria is responsible for the deaths of over half a million African children annually. Until a decade ago, dynamic analysis of the malaria parasite was limited to in vitro systems with the typical limitations associated with 2D monocultures or entirely artificial surfaces. Due to extremely low parasite densities, the liver was considered a black box in terms of Plasmodium sporozoite invasion, liver stage development, and merozoite release into the blood. Further, nothing was known about the behavior of blood stage parasites in organs such as the brain where clinical signs manifest and the ensuing immune response of the host that may ultimately result in a fatal outcome. The advent of fluorescent parasites, advances in imaging technology, and availability of an ever-increasing number of cellular and molecular probes have helped illuminate many steps along the pathogenetic cascade of this deadly tropical parasite.

In vivo confocal laser scanning microscopy and micropuncture in intact rat

BACKGROUND

Intravital microscopy theoretically provides the optimal conditions for studying specific organ functions. However, the application of microscopy in intact organs in vivo has been limited so far due to technical difficulties. The purpose of this study was to establish a method of in vivo confocal laser scanning microscopy (CLSM) for the study of endocytosis in proximal tubules of intact kidney.

METHODS

The left kidney of rats placed on a modified microscope stage was exposed and stabilized in a thermostatically controlled cup. The stage was then attached to an upright confocal microscope. Surface proximal tubules were microinfused with fluorescent albumin or transferrin. Single or time-series images of microinfused proximal tubules were recorded in reflection and/or fluorescence mode.

RESULTS

The stability of the kidney and the resolution of images were sufficient to visualize intracellular vesicles. Albumin and transferrin were initially observed at the brush border, then later internalized by proximal tubules and accumulated in lysosomes over a time period of 15 min. Furthermore, fusion of vesicles was observed in time-lapse images.

CONCLUSION

These results show that in vivo CLSM in intact kidney may be an excellent method to evaluate proximal tubular endocytosis and ligand trafficking.

Protective effects of a selective neutrophil elastase inhibitor (sivelestat) on lipopolysaccharide-induced acute dysfunction of the pulmonary microcirculation

OBJECTIVE

The purpose of this study was to evaluate the effect of a neutrophil elastase inhibitor, sivelestat, on lipopolysaccharide-induced acute lung injury through analysis of hemodynamic changes in the pulmonary microcirculation.

DESIGN

Randomized animal study.

SETTING

Medical school laboratory.

SUBJECTS

Twenty-seven Wistar rats (15 rats for microspectroscopic observations, 12 rats for measurements of neutrophil elastase activity and wet-to-dry ratio).

INTERVENTIONS

Thoracosternotomy was performed on male Wistar rats under continuous anesthesia and mechanical ventilation. Rats were divided into three groups (n = 5 each groups) on the basis of the reagent used: lipopolysaccharide group (100 microg/kg lipopolysaccharide intravenously), sivelestat group (10 mg/kg sivelestat; 100 microg/kg lipopolysaccharide intravenously), and control group (saline only, intravenously).

MEASUREMENTS AND MAIN RESULTS

We measured morphologic changes and hemodynamic variables, including tissue blood flow, erythrocyte velocity, erythrocyte count, thickness of interalveolar septa, and leukocyte adhesion in the pulmonary microcirculation, with a video-rate (33 msec/frame) dual-spot microspectroscopy system (DSMSS) and a laser-Doppler flowmeter. Blood-free wet-to-dry ratio and neutrophil elastase activity in bronchoalveolar lavage fluid, serum, and supernatant of lung homogenate were measured in another set of experiments (n = 4 for each group). Sixty minutes after lipopolysaccharide administration, severe thickening of the interalveolar septa was observed in the lipopolysaccharide but not the sivelestat group. In the lipopolysaccharide group, DSMSS measurements of erythrocyte velocity and hemoglobin oxygenation in single capillaries were decreased significantly (vs. control p < .05, vs. sivelestat p < .01), whereas tissue blood flow and erythrocyte velocity measurements from laser-Doppler flowmeter were increased significantly (vs. control p < .05, vs. sivelestat p < .01). The number of adherent leukocytes was increased significantly in the lipopolysaccharide group at 30, 45, and 60 mins after lipopolysaccharide administration (vs. control p < .01, vs. sivelestat p < .05). The number of adherent leukocytes did not increase in the sivelestat group. The wet-to-dry ratio was significantly higher in the lipopolysaccharide group than in control (p < .05) and sivelestat (p < .05) groups. Neutrophil elastase activities in the bronchoalveolar lavage fluid, serum, and lung tissue were all significantly lower in the sivelestat group than in the lipopolysaccharide group (p < .05).

CONCLUSIONS

Lipopolysaccharide induces leukocyte adhesion in the pulmonary microcirculation, resulting in decreased tissue hemoglobin oxygen and alveolar and interstitial edema. The selective neutrophil elastase inhibitor sivelestat reduces neutrophil elastase activity and attenuates acute changes in the pulmonary microcirculation.

Pulmonary microcirculation in mild and severe experimental pancreatitis

BACKGROUND

Research aimed at elucidating the pathogenesis of pancreatitis-associated lung injury and evaluating novel strategies for preventing respiratory complications in acute pancreatitis (AP) has not yet involved intravital microscopic (IVM) studies of pulmonary microcirculation in animals with severe disease.

OBJECTIVE

To characterize and compare pulmonary microcirculation in severe/necrotizing (NP) and mild/edematous pancreatitis (EP) in the rat.

METHODS

EP was induced by intravenous cerulein infusion (n = 10) and NP by a standardized intraductal infusion of glycodeoxycholic acid followed by intravenous cerulein (n = 10). After 24 h a left-sided thoracotomy was performed for IVM examination of pulmonary capillary blood flow, permeability, leukocyte sticking and the thickness of alveolar septi. Further measurements included monitoring of arterial blood gases and histological evaluation of lung injury.

RESULTS

In animals with NP, histology revealed severe pulmonary edema together with clustering of polymorphonuclear leukocytes in pulmonary microvessels and alveoli. IVM showed a greater number (n) of leukocytes sticking on the endothelium of pulmonary capillaries (9.4 +/- 0.7 vs. 1.8 +/- 0.2 in healthy control animals) and increased capillary permeability (260 +/- 14 vs. 136 +/- 6% relative fluorescein intensity) while capillary blood flow was decreased (0.41 +/- 0.05 vs. 0.57 +/- 0.03 mm/s). In comparison, changes in EP were significantly less pronounced (flow 0.5 +/- 0.04 mm/s, permeability 156 +/- 4%, leukocyte sticking n = 4.6 +/- 0.7).

CONCLUSIONS

These findings suggest that deterioration of pulmonary microcirculation in AP correlates with disease severity and that a model featuring NP may therefore be more suitable to further study pancreatitis-associated pulmonary injury.

Temporary unilateral microembolization of the lung-a new approach to regional chemotherapy for pulmonary metastases

BACKGROUND

Except in patients with resectable disease, treatment of pulmonary metastases is still disappointing. Regional chemotherapy may be a suitable method for delivering more effective doses to regionally confined tumors while minimizing systemic toxicity. We propose an unilateral chemoembolization of the lung applicable by endovascular method.

MATERIALS AND METHODS

An unilateral microembolization of the lung with degradable starch microspheres (DSM) alone (group 1) and combined with carboplatin (group 2) was performed on Sprague-Dawley rats (n = 12). Microcirculatory parameters were studied by in vivo videomicroscopy and radiological pattern on pulmonary angiogram.

RESULTS

After injection of DSM, mean embolization time in subpleural capillaries was 7.1 +/- 2.3 min, followed by a mean flow retardation of 14.3 +/- 4.6 min; 21.4 +/- 4.7 min after embolization, original flow of erythrocytes was observed demonstrating reperfusion and reversibility of microembolization. After reperfusion relative fluorescence measured in subpleural alveoli was 0.13 +/- 0.049 in group 1, 0.105 +/- 0.016 in group 2, and 0.11 +/- 0.036 in control group (NS). Alveolar septal diameter was 17.3 +/- 1.13 microm in group 1, 16.8 +/- 1.25 microm in group 2, and 16.6 +/- 1.08 microm in control group (NS), demonstrating neither altered permeability nor pulmonary edema. Pulmonary angiogram confirmed patency of the central pulmonary artery.

CONCLUSION

For the first time unilateral microembolization of the lung could be established in an experimental model. By injection of DSM, reversible embolization on arteriolar and capillary level could be demonstrated without occlusion of the main branches of the pulmonary arteries. Alveolar-capillary membrane disorder as symptom of early toxicity could not be detected even with additional application of carboplatin.