Comparison of newly developed inhalation anesthesia system and intraperitoneal anesthesia on the hemodynamic state in mice

Rest/stress myocardial perfusion imaging by positron emission tomography with 18F-Flurpiridaz: A feasibility study in mice

BACKGROUND

Myocardial perfusion imaging by positron emission tomography (PET-MPI) is the current gold standard for quantification of myocardial blood flow. 18F-flurpiridaz was recently introduced as a valid alternative to currently used PET-MPI probes. Nonetheless, optimum scan duration and time interval for image analysis are currently unknown. Further, it is unclear whether rest/stress PET-MPI with 18F-flurpiridaz is feasible in mice.

METHODS

Rest/stress PET-MPI was performed with 18F-flurpiridaz (0.6-3.0 MBq) in 27 mice aged 7-8 months. Regadenoson (0.1 µg/g) was used for induction of vasodilator stress. Kinetic modeling was performed using a metabolite-corrected arterial input function. Image-derived myocardial 18F-flurpiridaz uptake was assessed for different time intervals by placing a volume of interest in the left ventricular myocardium.

RESULTS

Tracer kinetics were best described by a two-tissue compartment model. K1 ranged from 6.7 to 20.0 mL·cm-3·min-1, while myocardial volumes of distribution (VT) were between 34.6 and 83.6 mL·cm-3. Of note, myocardial 18F-flurpiridaz uptake (%ID/g) was significantly correlated with K1 at rest and following pharmacological vasodilation for all time intervals assessed. However, while Spearman's coefficients (rs) ranged between 0.478 and 0.681, R2 values were generally low. In contrast, an excellent correlation of myocardial 18F-flurpiridaz uptake with VT was obtained, particularly when employing the averaged myocardial uptake from 20 to 40 min post tracer injection (R2 ≥ 0.98). Notably, K1 and VT were similarly sensitive to pharmacological vasodilation induction. Further, mean stress-to-rest ratios of K1, VT, and %ID/g 18F-flurpiridaz were virtually identical, suggesting that %ID/g 18F-flurpiridaz can be used to estimate coronary flow reserve (CFR) in mice.

CONCLUSION

Our findings suggest that a simplified assessment of relative myocardial perfusion and CFR, based on image-derived tracer uptake, is feasible with 18F-flurpiridaz in mice, enabling high-throughput mechanistic CFR studies in rodents.

Multiphoton Phosphorescence Quenching Microscopy Reveals Kinetics of Tumor Oxygenation during Antiangiogenesis and Angiotensin Signaling Inhibition

PURPOSE

The abnormal function of tumor blood vessels causes tissue hypoxia, promoting disease progression and treatment resistance. Although tumor microenvironment normalization strategies can alleviate hypoxia globally, how local oxygen levels change is not known because of the inability to longitudinally assess vascular and interstitial oxygen in tumors with sufficient resolution. Understanding the spatial and temporal heterogeneity should help improve the outcome of various normalization strategies.

EXPERIMENTAL DESIGN

We developed a multiphoton phosphorescence quenching microscopy system using a low-molecular-weight palladium porphyrin probe to measure perfused vessels, oxygen tension, and their spatial correlations in vivo in mouse skin, bone marrow, and four different tumor models. Further, we measured the temporal and spatial changes in oxygen and vessel perfusion in tumors in response to an anti-VEGFR2 antibody (DC101) and an angiotensin-receptor blocker (losartan).

RESULTS

We found that vessel function was highly dependent on tumor type. Although some tumors had vessels with greater oxygen-carrying ability than those of normal skin, most tumors had inefficient vessels. Further, intervessel heterogeneity in tumors is associated with heterogeneous response to DC101 and losartan. Using both vascular and stromal normalizing agents, we show that spatial heterogeneity in oxygen levels persists, even with reductions in mean extravascular hypoxia.

CONCLUSIONS

High-resolution spatial and temporal responses of tumor vessels to two agents known to improve vascular perfusion globally reveal spatially heterogeneous changes in vessel structure and function. These dynamic vascular changes should be considered in optimizing the dose and schedule of vascular and stromal normalizing strategies to improve the therapeutic outcome.

Role of sex hormones in modulating myocardial perfusion and coronary flow reserve

Background

A growing body of evidence highlights sex differences in the diagnostic accuracy of cardiovascular imaging modalities. Nonetheless, the role of sex hormones in modulating myocardial perfusion and coronary flow reserve (CFR) is currently unclear. The aim of our study was to assess the impact of female and male sex hormones on myocardial perfusion and CFR.

Methods

Rest and stress myocardial perfusion imaging (MPI) was conducted by small animal positron emission tomography (PET) with [¹⁸F]flurpiridaz in a total of 56 mice (7–8 months old) including gonadectomized (Gx) and sham-operated males and females, respectively. Myocardial [¹⁸F]flurpiridaz uptake (% injected dose per mL, % ID/mL) was used as a surrogate for myocardial perfusion at rest and following intravenous regadenoson injection, as previously reported. Apparent coronary flow reserve (CFR_App) was calculated as the ratio of stress and rest myocardial perfusion. Left ventricular (LV) morphology and function were assessed by cardiac magnetic resonance (CMR) imaging.

Results

Orchiectomy resulted in a significant decrease of resting myocardial perfusion (Gx vs. sham, 19.4 ± 1.0 vs. 22.2 ± 0.7 % ID/mL, p = 0.034), while myocardial perfusion at stress remained unchanged (Gx vs. sham, 27.5 ± 1.2 vs. 27.3 ± 1.2 % ID/mL, p = 0.896). Accordingly, CFR_App was substantially higher in orchiectomized males (Gx vs. sham, 1.43 ± 0.04 vs. 1.23 ± 0.05, p = 0.004), and low serum testosterone levels were linked to a blunted resting myocardial perfusion (r = 0.438, p = 0.020) as well as an enhanced CFR_App (r = −0.500, p = 0.007). In contrast, oophorectomy did not affect myocardial perfusion in females. Of note, orchiectomized males showed a reduced LV mass, stroke volume, and left ventricular ejection fraction (LVEF) on CMR, while no such effects were observed in oophorectomized females.

Conclusion

Our experimental data in mice indicate that sex differences in myocardial perfusion are primarily driven by testosterone. Given the diagnostic importance of PET-MPI in clinical routine, further studies are warranted to determine whether testosterone levels affect the interpretation of myocardial perfusion findings in patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05675-2.

Mouse Anesthesia: The Art and Science

There is an art and science to performing mouse anesthesia, which is a significant component to animal research. Frequently, anesthesia is one vital step of many over the course of a research project spanning weeks, months, or beyond. It is critical to perform anesthesia according to the approved research protocol using appropriately handled and administered pharmaceutical-grade compounds whenever possible. Sufficient documentation of the anesthetic event and procedure should also be performed to meet the legal, ethical, and research reproducibility obligations. However, this regulatory and documentation process may lead to the use of a few possibly oversimplified anesthetic protocols used for mouse procedures and anesthesia. Although a frequently used anesthetic protocol may work perfectly for each mouse anesthetized, sometimes unexpected complications will arise, and quick adjustments to the anesthetic depth and support provided will be required. As an old saying goes, anesthesia is 99% boredom and 1% sheer terror. The purpose of this review article is to discuss the science of mouse anesthesia together with the art of applying these anesthetic techniques to provide readers with the knowledge needed for successful anesthetic procedures. The authors include experiences in mouse inhalant and injectable anesthesia, peri-anesthetic monitoring, specific procedures, and treating common complications. This article utilizes key points for easy access of important messages and authors’ recommendation based on the authors’ clinical experiences.

Use of an Integrated Low-Flow Anesthetic Vaporizer, Ventilator, and Physiological Monitoring System for Rodents

Low-flow digital vaporizers commonly utilize a syringe pump to directly administer volatile anesthetics into a stream of carrier gas. Per animal welfare recommendations, animals are warmed and monitored during procedures requiring anesthesia. Common anesthesia and physiological monitoring equipment include gas tanks, anesthetic vaporizers and stands, warming controllers and pads, mechanical ventilators, and pulse oximeters. A computer is also necessary for data collection and to run equipment software. In smaller spaces or when performing field work, it can be challenging to configure all this equipment in limited space. The goal of this protocol is to demonstrate best practices for use of a low-flow digital vaporizer using both compressed oxygen and room air, along with an integrated mechanical ventilator, pulse oximeter, and far infrared warming as an all-inclusive anesthesia and physiological monitoring suite ideal for rodents.

General Anesthetic-Induced Neurotoxicity in the Immature Brain: Reevaluating the Confounding Factors in the Preclinical Studies

General anesthetic (GA) is used clinically to millions of young children each year to facilitate surgical procedures, relieve perioperative stress, and provide analgesia and amnesia. During recent years, there is a growing concern regarding a causal association between early life GA exposure and subsequently long-term neurocognitive abnormalities. To address the increasing concern, mounting preclinical studies and clinical trials have been undergoing. Until now, nearly all of the preclinical findings show that neonatal exposure to GA causally leads to acute neural cell injury and delayed cognitive impairment. Unexpectedly, several influential clinical findings suggest that early life GA exposure, especially brief and single exposure, does not cause adverse neurodevelopmental outcome, which is not fully in line with the experimental findings and data from several previous cohort trials. As the clinical data have been critically discussed in previous reviews, in the present review, we try to analyze the potential factors of the experimental studies that may overestimate the adverse effect of GA on the developing brain. Meanwhile, we briefly summarized the advance in experimental research. Generally, our purpose is to provide some useful suggestions for forthcoming preclinical studies and strengthen the powerfulness of preclinical data.

Impacts of Different Anesthetic Agents on Left Ventricular Systolic Function in Mice Assessed by Echocardiography

The present experiments were performed to study the effects and time trends of different anesthetic agents on the left ventricular (LV) systolic function and heart rate by high-resolution echocardiography in mice. Ten male C57BL/6J mice were submitted to echocardiography imaging separated by 72-hour intervals under the following conditions: 1) conscious mice, 2) mice anesthetized with isoflurane (ISO, inhaled), 3) mice anesthetized with tribromoethanol (TBE, intraperitoneal), 4) mice anesthetized with chloral hydrate (CH, intraperitoneal), and 5) mice anesthetized with pentobarbital sodium (PS, intraperitoneal). The effect of ISO, TBE, CH, and PS on LV systolic function was measured at 0, 1, 2, 3, 4, 6, 8, and 10 min after anesthesia. The results showed that LV systolic function and heart rate (HR) of anesthetized mice were reduced significantly (P<0.05), compared with results in the same mice studied in the conscious state. In addition, the results indicated that the anesthetic with the least effect on LV function was CH, and followed by TBE, PS, ISO. We conclude that different anesthetic agents always depressed the HR and LV systolic function of mice, and, furthermore, the effects and time trends of different anesthetics on LV function are different. In echocardiographic experiments, we should choose proper anesthetic agents according to the experimental requirements.

Test-retest reproducibility of cardiac magnetic resonance imaging in healthy mice at 7-Tesla: effect of anesthetic procedures

Cardiac magnetic resonance (CMR) has emerged as a powerful tool for in vivo assessments of cardiac parameters in experimental animal models of cardiovascular diseases, but its reproducibility in this setting remains poorly explored. To address this issue, we investigated the test-retest reproducibility of preclinical cardiac magnetic resonance imaging (CMR) at 7 Tesla in healthy C57BL/6 mice, including an analysis of the impact of different anesthetic procedures (isoflurane or pentobarbital). We also analyzed the intra-study reproducibility and the intra- and inter-observer post-processing reproducibility of CMR images. Test-retest reproducibility was high for left ventricular parameters, especially with the isoflurane anesthetic procedure, whereas right ventricular parameters and deformation measurements were less reproducible, mainly due to physiological variability. Post-processing reproducibility of CMR images was high both within and between observers. These results highlight that anesthetic procedures might influence CMR test-retest reproducibility, an important ethical consideration for longitudinal studies in rodent models of cardiomyopathy to limit the number of animals used.

Mir30c Is Involved in Diabetic Cardiomyopathy through Regulation of Cardiac Autophagy via BECN1

Multiple factors have been shown to promote the progression of diabetic cardiomyopathy. A link has previously been found between Mir30 and autophagy in cancer cells and in the heart, but the role of Mir30 in diabetic heart has not been studied. Using in vitro and in vivo approaches, we found that the depletion of Mir30c and induction of BECN1 enhanced autophagy in diabetic (db/db) hearts and in cardiomyocytes treated with the fatty acid palmitate. We verified that Mir30c repressed BECN1 expression by direct binding to the BECN1 3' UTRs. Mir30c overexpression inhibited the induction of BECN1 and subsequent autophagy in diabetic hearts and improved cardiac function and structure in diabetic mice. However, these effects were abrogated by BECN1 overexpression. Similarly, Mir30c knockdown resulted in increased BECN1 levels and autophagic flux, aggravating cardiac abnormalities. We also show that SP1, an important transcriptional factor in energy metabolism regulation, is a key upstream activator of Mir30c that binds the promoter region of Mir30c. Our findings indicate that downregulation of Mir30c and subsequent activation of BECN1 promotes autophagy, contributing to the pathogenesis of diabetic cardiomyopathy. This observation suggests a theoretical ground for developing microRNA-based therapeutics against diabetic cardiomyopathy by inhibiting autophagy.

Use of a Low-flow Digital Anesthesia System for Mice and Rats

A traditional vaporizer depends on flowing gas and atmospheric pressure for passive anesthetic vaporization. Newly developed direct injection vaporizers utilize a syringe pump to directly administer volatile anesthetics into a gas stream. Unlike a traditional vaporizer, it can be used at very low flow rates, making it ideal for use on mice and rats. The equipment's capability to use low flow rates could result in a substantial cost savings due to the reduced need for anesthetic agents, compressed gas, and charcoal scavenging filters(1). A lower flow rate means less waste of anesthetic gas and likely reduces the risk of anesthetic exposure to laboratory personnel. Thus, the high levels of precision and safety associated with direct injection vaporizers, along with a reduced need for anesthetic agents, compressed gas, and charcoal filters are beneficial for research requiring small animal anesthesia. The goal of this protocol is to demonstrate the use of a syringe-driven direct injection vaporizer as part of a digital, low-flow anesthesia system. The direct injection vaporizer is capable of accurately delivering anesthesia at very low flow rates compared to a traditional vaporizer, making it a promising alternative for controlled gas anesthetic delivery to rodents.

Effect of different anesthetic agents on left ventricular systolic function assessed by echocardiography in hamsters

Determination of left ventricular ejection fraction (LVEF) using in vivo imaging is the cardiac functional parameter most frequently employed in preclinical research. However, there is considerable conflict regarding the effects of anesthetic agents on LVEF. This study aimed at assessing the effects of various anesthetic agents on LVEF in hamsters using transthoracic echocardiography. Twelve female hamsters were submitted to echocardiography imaging separated by 1-week intervals under the following conditions: 1) conscious animals, 2) animals anesthetized with isoflurane (inhaled ISO, 3 L/min), 3) animals anesthetized with thiopental (TP, 50 mg/kg, intraperitoneal), and 4) animals anesthetized with 100 mg/kg ketamine plus 10 mg/kg xylazine injected intramuscularly (K/X). LVEF obtained under the effect of anesthetics (ISO=62.2±3.1%, TP=66.2±2.7% and K/X=75.8±1.6%) was significantly lower than that obtained in conscious animals (87.5±1.7%, P<0.0001). The K/X combination elicited significantly higher LVEF values compared to ISO (P<0.001) and TP (P<0.05). K/X was associated with a lower dispersion of individual LVEF values compared to the other anesthetics. Under K/X, the left ventricular end diastolic diameter (LVdD) was increased (0.60±0.01 cm) compared to conscious animals (0.41±0.02 cm), ISO (0.51±0.02 cm), and TP (0.55±0.01 cm), P<0.0001. The heart rate observed with K/X was significantly lower than in the remaining conditions. These results indicate that the K/X combination may be the best anesthetic option for the in vivo assessment of cardiac systolic function in hamsters, being associated with a lower LVEF reduction compared to the other agents and showing values closer to those of conscious animals with a lower dispersion of results.

Effects of anesthesia on conventional and speckle tracking echocardiographic parameters in a mouse model of pressure overload

Genetically-modified mice are widely applied in cardiovascular studies as model organisms. Echocardiography is a key tool for evaluating cardiac and hemodynamic functions in mice. The present study aimed to examine the effects of isoflurane (ISF) on conventional and speckle tracking echocardiography (STE) parameters under healthy and pathological conditions using a murine model of pressure overload. In addition, the optimal dose of ISF in the process of echocardiographic measurement, with minimum cardiac contraction depression, was investigated. Conventional echocardiographic and STE examinations were performed on 38 adult C57BL/6 male mice. The mice were divided into the following three groups: The sham (n=15); mild thoracic aortic banding (TAB; n=15); and severe TAB (n=8) groups. ISF was administered under deep anesthesia (DA; 1-2% ISF), light anesthesia (LA; 0.5-1% ISF) and immediately prior to the mice waking up (awake; 0-0.5% ISF). Conventional echocardiographic parameters were preserved within the sham and mild TAB groups (P>0.05 for each parameter) under LA and awake conditions. However, under DA conditions, the majority of these parameters were reduced compared with the LA and awake conditions (P<0.05). In the severe TAB group, conventional echocardiographic parameters remained constant under LA, DA and awake conditions. STE parameters in the groups remained similar between the LA and awake conditions, but were significantly reduced under DA conditions. Therefore, conventional echocardiography and STE may be performed using LA induced with low doses of ISF, under various pathological conditions without affecting cardiac function.

Speckle tracking echocardiography in the diagnosis of early left ventricular systolic dysfunction in type II diabetic mice

Background

The leptin receptor-deficient db/db mouse is a well-established type II diabetes animal model used to investigate diabetic cardiomyopathy. Previous reports have documented diabetic cardiomyopathy is accompanied by cardiac structural and functional abnormalities. To better elucidate early or subtle changes in cardiac performance in db/db mice, we used speckle tracking echocardiography to assess systolic myocardial strain in vivo with diabetic db/db mice in order to study early changes of left ventricle contractile function in type II diabetes model.

Methods

Male diabetic db/db mice and age-matched control mice from C57BL/6J strain at 8,12 and 16 weeks of age were subjected to echocardiography. At the midpapillary level in the parasternal left ventricular short-axis view, end diastolic and systolic left ventricular diameter, interventricular septal thickness and posterior wall thicknesses, ejection fraction, fractional shortening were determined by M-mode echocardiography. Using speckle-tracking based strain analysis of two-dimensional echocardiographic images acquired from the parasternal short-axis views at the mid-papillary level, systolic global radial and circumferential strain values were analyzed.

Results

There was no significant difference in interventricular septal thickness, posterior wall thicknesses, end diastolic and systolic left ventricular diameter, ejection fraction and fractional shortening between db/db and age-matched control mice at 8,12 or 16 weeks of age (P > 0.05). At 8 and 12 weeks of age, there was no significant difference in left ventricular radial strain and circumferential strain between db/db mice and age-matched controls (P > 0.05). But at 16 weeks of age, the left ventricular radial strain and circumferential strain in db/db mice were lower than in control mice (P < 0.01).

Conclusion

The present study shows that speckle tracking echocardiography can be used to evaluate cardiac functional alterations in mouse models of cardiovascular disease. Radial and circumferential strain are more sensitive and can be used for detection of early left ventricular contractile dysfunction in db/db type II diabetic mice.

Doppler parameters of fetal lung hypoplasia and impact of sildenafil

OBJECTIVE

Congenital diaphragmatic hernia (CDH) is clinically challenging because of associated lung hypoplasia (LH). There have been no validated parameters to evaluate fetal LH severity. Sildenafil has been shown to improve LH mass in nitrofen-induced pulmonary artery (PA) models, but the pulmonary vascular tone has not been evaluated in vivo. The aim of this study was to identify the PA Doppler parameter that best predicts LH severity and to investigate the efficacy of antenatal sildenafil treatment in experimental CDH.

STUDY DESIGN

Nitrofen (50-60% CDH in offspring) or vehicle on E9.5 and sildenafil or vehicle on E11.5-20.5 were administrated to pregnant rats. On E20.5, PA Doppler indices were investigated with and without maternal hyperoxia. The presence/absence of CDH, lung/body weight ratio and radial saccular count were assessed at E20.5.

RESULTS

At baseline, CDH rats had lower PA Doppler acceleration/ejection time ratios and pulsatility index (PI). Maternal hyperoxia resulted in a significant decrease in the PA/PI suggesting pulmonary vasodilation. In contrast, in CDH fetuses, the ipsilateral PA/PI showed little or no response to hyperoxia (P > .05), and in those with LH, PI response to maternal hyperoxia correlated positively with hernia, lung/body weight ratio (r = 0.70, P = .01). Maternal sildenafil therapy significantly improved PA response to hyperoxia and lung growth in CDH fetuses (P < .01).

CONCLUSION

Pulmonary vasodilation that occurs in E20.5 fetal rats in response to maternal hyperoxia is blunted in CDH. Change in PA/PI with hyperoxia is a useful predictor of LH severity. Sildenafil improves pulmonary vascular response and lung growth in fetal CDH.

Imaging windows for long-term intravital imaging: General overview and technical insights

Intravital microscopy is increasingly used to visualize and quantitate dynamic biological processes at the (sub)cellular level in live animals. By visualizing tissues through imaging windows, individual cells (e.g., cancer, host, or stem cells) can be tracked and studied over a time-span of days to months. Several imaging windows have been developed to access tissues including the brain, superficial fascia, mammary glands, liver, kidney, pancreas, and small intestine among others. Here, we review the development of imaging windows and compare the most commonly used long-term imaging windows for cancer biology: the cranial imaging window, the dorsal skin fold chamber, the mammary imaging window, and the abdominal imaging window. Moreover, we provide technical details, considerations, and trouble-shooting tips on the surgical procedures and microscopy setups for each imaging window and explain different strategies to assure imaging of the same area over multiple imaging sessions. This review aims to be a useful resource for establishing the long-term intravital imaging procedure.

Protective effects of losartan in mice with chronic viral myocarditis induced by coxsackievirus B3

AIM

To investigate whether losartan has protective effects in mice with chronic viral myocarditis induced by coxsackievirus B3 (CVB3).

MAIN METHODS

Thirty two male Balb/c mice were intraperitoneally injected with CVB3 (10×TCID50) to induce chronic viral myocarditis (CVM). Losartan at 12.5mg/kg (n=16) or normal saline (n=16) were orally administered daily for 28 days to these mice. Uninfected mice (n=6) were used as controls. On day 29, all mice underwent anesthesia and echocardiography prior to sacrifice. Serum IL-17, IL-4, IFN-γ and TNF-α levels were measured by enzyme-linked immunosorbent assay, and cardiac tissues were histologically examined after hematoxylin & eosin staining. In addition, the effect of losartan on the virus titers in primary cultured neonatal rat cardiomyocytes infected with CVB3 was measured on Hep-2 cells at 72 h post infection.

KEY FINDINGS

Mice infected with CBV3 had significantly increased mortality, heart/body weight ratios, necrosis and inflammatory scores and decreased cardiac ejection fractions, compared with the controls (all P<0.05). Losartan significantly decreased mortality from 40.0% to 12.5%, heart/body weight ratios from 7.08 ± 2.17 to 4.15 ± 0.99, and necrosis and inflammatory scores from 3.33 ± 0.50 to 2.50 ± 0.65 (all P<0.05), and increased ejection fractions from 55.80 ± 9.25 to 72.31 ± 12.15 (P<0.05). Losartan significantly enhanced IL-4, and decreased IFN-γ, TNF-α and IL-17 (all P<0.05). In the in vitro experiment, losartan had no influence on virus titers.

SIGNIFICANCE

Losartan protects mice against CVB3-induced CVM, most likely through upregulating Th2 responses, and down-regulating Th1 and Th17 responses.

Inhibition of firefly luciferase by general anesthetics: effect on in vitro and in vivo bioluminescence imaging

Bioluminescence imaging is routinely performed in anesthetized mice. Often isoflurane anesthesia is used because of its ease of use and fast induction/recovery. However, general anesthetics have been described as important inhibitors of the luciferase enzyme reaction.

Aim

To investigate frequently used mouse anesthetics for their direct effect on the luciferase reaction, both in vitro and in vivo.

Materials and Methods

isoflurane, sevoflurane, desflurane, ketamine, xylazine, medetomidine, pentobarbital and avertin were tested in vitro on luciferase-expressing intact cells, and for non-volatile anesthetics on intact cells and cell lysates. In vivo, isoflurane was compared to unanesthetized animals and different anesthetics. Differences in maximal photon emission and time-to-peak photon emission were analyzed.

Results

All volatile anesthetics showed a clear inhibitory effect on the luciferase activity of 50% at physiological concentrations. Avertin had a stronger inhibitory effect of 80%. For ketamine and xylazine, increased photon emission was observed in intact cells, but this was not present in cell lysate assays, and was most likely due to cell toxicity and increased cell membrane permeability. In vivo, the highest signal intensities were measured in unanesthetized mice and pentobarbital anesthetized mice, followed by avertin. Isoflurane and ketamine/medetomidine anesthetized mice showed the lowest photon emission (40% of unanesthetized), with significantly longer time-to-peak than unanesthetized, pentobarbital or avertin-anesthetized mice. We conclude that, although strong inhibitory effects of anesthetics are present in vitro, their effect on in vivo BLI quantification is mainly due to their hemodynamic effects on mice and only to a lesser extent due to the direct inhibitory effect.

Effects of heart rate and anesthetic timing on high-resolution echocardiographic assessment under isoflurane anesthesia in mice

OBJECTIVE

Anesthesia provides sedation and immobility, facilitating echocardiography in mice, but it influences cardiovascular function and therefore outcomes of measurement. This study aimed to determine the effect of the optimal heart rate (HR) and anesthetic timing on echocardiographic reproducibility under isoflurane anesthesia.

METHODS

Male C57BL/6J mice underwent high-resolution echocardiography with relative fixed HRs and anesthetic timing. The same experiment was repeated once again after 1 week.

RESULTS

Echocardiography was highly reproducible in repeated measurements under low-HR (350-400 beats per minute [bpm]) and high-HR (475-525 bpm) conditions except some M-mode parameters under low-HR conditions. With similar anesthetic timing, mice with a high HR had decreased preload indices and increased ejection phase and Doppler indices. Inversely, when the HR was similar, the echocardiographic results of mice under short anesthetic timing showed little difference from the ones under long anesthetic timing.

CONCLUSIONS

This study shows that echocardiographic assessment is greatly reproducible under a high HR. The HR is more important than anesthetic timing for echocardiographic evaluation in mice.

Isoflurane and sevoflurane provide equally effective anaesthesia in laboratory mice

Isoflurane is currently the most common volatile anaesthetic used in laboratory mice, whereas in human medicine the more modern sevoflurane is often used for inhalation anaesthesia. This study aimed to characterize and compare the clinical properties of both anaesthetics for inhalation anaesthesia in mice. In an approach mirroring routine laboratory conditions (spontaneous breathing, gas supply via nose mask, preventing hypothermia by a warming mat) a 50 min anaesthesia was performed. Anaesthetics were administered in oxygen as carrier gas at standardized dosages of 1.5 minimum alveolar concentrations, which was 2.8% for isoflurane and 4.9% for sevoflurane. Both induction and recovery from anaesthesia proceeded quickly, within 1-2 min. During anaesthesia, all reflex testing was negative and no serious impairment of vital functions was found; all animals survived. The most prominent side-effect during anaesthesia was respiratory depression with hypercapnia, acidosis and a marked decrease in respiration rate. Under anaesthesia, heart rate and core body temperature remained within the normal range, but were significantly increased for 12 h after anaesthesia. Locomotor activity, daily food and water consumption and body weight progression showed no abnormalities after anaesthesia. No significant difference was found between the two anaesthetics. In conclusion, isoflurane and sevoflurane provided an equally reliable anaesthesia in laboratory mice.

Left ventricular function in the post-infarct failing mouse heart by magnetic resonance imaging and conductance catheter: a comparative analysis

AIM

Murine myocardial infarction (MI) models are increasingly used in heart failure studies. Magnetic resonance imaging (MRI) and pressure-volume loops by conductance catheter (CC) enable physiological phenotyping. We performed a comparative analysis of MRI vs. CC to assess left ventricular (LV) function in the failing mouse heart.

METHODS

MI was created by LAD ligation. MRI (day 14) and CC (day 15) were used to determine LV end-diastolic volume (EDV), end-systolic volume (ESV) and ejection fraction (EF).

RESULTS

Pooled data yielded moderate-to-strong linear correlations: EDV: R = 0.61; ESV: R = 0.72; EF: R = 0.81. We analysed three groups, no MI (sham, n = 10), small MI (<30% of LV, n = 14) and large MI (>30%, n = 20). Volumes and EF were consistently lower by CC than by MRI, but group differences were evident for both techniques. Receiver-operating characteristic analysis indicated good sensitivity and specificity for both techniques, with superior results for MRI.

CONCLUSIONS

CC and MRI are highly valuable for evaluation of LV volume and function. MRI is recommended for longitudinal studies, accurate absolute volumes and anatomical information. Unique features of CC are its online signal with high temporal resolution, and advanced analysis of LV function and energetics.