Effect of midazolam and butorphanol premedication on inhalant isoflurane anesthesia in mice

Short-term dynamics of fecal microbiome and antibiotic resistance in juvenile rainbow trout (Oncorhynchus mykiss) following antibiotic treatment and withdrawal

BACKGROUND

In aquaculture, the secretions of cultured organisms contribute to the development of aquatic antibiotic resistance. However, the antibiotic-induced changes in fish feces remain poorly understood. This study aimed to assess the short-term dynamics of fecal microbiome and antibiotic resistance in juvenile rainbow trout (Oncorhynchus mykiss) upon antibiotic treatment and withdrawal period.

METHODS

Fish were orally administered diets supplemented with oxytetracycline (OTC) or sulfadiazine/trimethoprim (SDZ/TMP) for 10 consecutive days, followed by a 25-day withdrawal period. Fecal samples were collected before antibiotic treatment (day 0), and at 1, 3, 7, and 10 days post antibiotic administration (dpa), as well as 1, 3, 7, 14, and 25 days post antibiotic cessation (dpc). The fecal microbiome community was profiled using both culture-dependent and -independent methods. The relative abundance of antibiotic resistance genes (ARGs) and the class 1 integron-integrase gene (intI1) in the feces were quantified using real-time PCR.

RESULTS

Antibiotic treatment disrupted the fecal microbial communities, and this alteration persisted even after antibiotic cessation. Moreover, OTC treatment increased the relative abundance of tet genes, while sul and dfr genes increased in the SDZ/TMP-treated group. Notably, Flavobacterium, Pseudomonas, and Streptococcus exhibited a significant correlation with the abundance of ARGs, suggesting their potential role as carriers for ARGs.

CONCLUSION

This study demonstrates the antibiotic-induced changes in the fecal microbiome and the increase of ARGs in rainbow trout feces. These findings provide novel insights into the dynamics of microbiome recovery post-antibiotic cessation and suggest that fish feces provide a non-invasive approach to predict changes in the fish gut microbiome and resistome.

Butorphanol inhibits ferroptosis to attenuate PC12 cell injury by blocking JNK/p38 signaling

Butorphanol is a synthetic selective opioid receptor antagonist that exhibits substantial analgesic effects. The present study aimed to explore the effects of butorphanol on a neurodegenerative disease cell model and to investigate its specific regulatory mechanism. Cell viability of PC12 cells was assessed using the Cell Counting Kit-8 assay. Oxidative stress levels were measured by the corresponding kits and western blotting of specific protein markers. Apoptosis was determined using the terminal-deoxynucleoitidyl transferase mediated nick end labeling assay and by western blotting. Western blotting was used to analyze the expression levels of c-Jun NH2-terminal kinase (JNK)/p38 signaling pathway-related proteins. Thiobarbituric acid-reactive substances and Fe+2 content were detected using the corresponding assay kits and the expression levels of ferroptosis-associated proteins were assessed by western blotting following the addition of the JNK activator anisomycin (ANI). Oxidative stress and apoptosis were examined with the aforementioned assays following the supplementation of ANI or the ferroptosis inducer erastin (ERA). It was revealed that butorphanol dose-dependently enhanced the viability and suppressed the oxidative stress and apoptosis of H2O2-treated PC12 cells. In addition, butorphanol blocked JNK/p38 signaling and hampered ferroptosis, while this effect was reversed by ANI. ANI or ERA reversed the effects of butorphanol on oxidative stress and apoptosis of H2O2-treated PC12 cells. In summary, butorphanol suppressed ferroptosis by blocking JNK/p38 signaling to impart inhibitory effects on oxidative stress and apoptosis in a neurodegenerative disease cell model.

Use of Ketamine or Xylazine to Provide Balanced Anesthesia with Isoflurane in C57BL/6J Mice

Balanced anesthesia-the use of a combination of drugs to achieve a desired anesthetic plane-offers many benefits, including smoother induction and recovery and fewer adverse effects than occur with individual drugs. Although premedication prior to inhalant anesthesia is routine in other species, mice are commonly induced with gas anesthesia alone. The hypothesis of this study was that premedication with ketamine or xylazine would safely reduce the stress of isoflurane induction and lower the minimum alveolar concentration (MAC) of isoflurane. Young adult male and female C57BL/6J mice were premedicated with ketamine (100 mg/kg), xylazine (4 mg/kg), or isotonic crystalloid (0.1 mL) and were used in 4 experiments. First, isoflurane induction was video recorded under all test conditions, and the videos were scored according to a behavioral ethogram to identify signs of distress. Mice in the ketamine group experienced tremors and ataxia before and dur- ing induction. Therefore, ketamine was given after induction with isoflurane in subsequent experiments. Second, the MAC value for each anesthetic protocol was determined by using quantal and bracketing analysis. Third, mice were anesthetized according to the 3 protocols, and vital parameters were monitored for 60 min. Finally, anesthetized mice were challenged with hypoxia and hypovolemia, and vital parameters were monitored. Premedication with xylazine significantly reduced the stress scores for isoflurane induction (control, 7.3 ± 1.5; ketamine, 6.0 ± 3.0; xylazine, 3.1 ± 1.0). Ketamine and xylazine both reduced the MAC of isoflurane (control, 1.89%; ketamine, 0.96%; xylazine, 1.20%). All mice survived 60 min of anesthesia and the hypoxia-hypovolemia challenge. Premedication with xylazine reduced the stress of induction and lowered the necessary dose of isoflurane in C57BL/6J mice to maintain a surgical plane of anesthesia. We recommend administering xylazine before isoflurane induction and anesthesia of healthy mice that are undergoing procedures in which 100% oxygen is provided and anticipated blood loss is less than 10% to 15% of the total blood volume.

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.

Comparative Metagenomic Analysis of Chicken Gut Microbial Community, Function, and Resistome to Evaluate Noninvasive and Cecal Sampling Resources

When conducting metagenomic analysis on gut microbiomes, there is no general consensus concerning the mode of sampling: non-contact (feces), noninvasive (rectal swabs), or cecal. This study aimed to determine the feasibility and comparative merits and disadvantages of using fecal samples or rectal swabs as a proxy for the cecal microbiome. Using broiler as a model, gut microbiomes were obtained from cecal, cloacal, and fecal samples and were characterized according to an analysis of the microbial community, function, and resistome. Cecal samples had higher microbial diversity than feces, while the cecum and cloaca exhibited higher levels of microbial community structure similarity compared with fecal samples. Cecal microbiota possessed higher levels of DNA replicative viability than feces, while fecal microbiota were correlated with increased metabolic activity. When feces were excreted, the abundance of antibiotic resistance genes like tet and ErmG decreased, but some antibiotic genes became more prevalent, such as fexA, tetL, and vatE. Interestingly, Lactobacillus was a dominant bacterial genus in feces that led to differences in microbial community structure, metabolism, and resistome. In conclusion, fecal microbiota have limited potential as a proxy in chicken gut microbial community studies. Thus, feces should be used with caution for characterizing gut microbiomes by metagenomic analysis.

Therapeutic Effect of an Anti-Human Programmed Death-Ligand 1 (PD-L1) Nanobody on Polymicrobial Sepsis in Humanized Mice

BACKGROUND Immunosuppression is regarded as the main cause of death induced by sepsis. Anti-programmed death-ligand 1 (PD-L1) therapy is promising in reversing sepsis-induced immunosuppression but no evidence is available on use of commercially available anti-PD-L1 medications for this indication. The present preclinical study was performed to investigate the therapeutic effect of an anti-PD-L1 nanobody (KN035) in sepsis. MATERIAL AND METHODS The level of expression of PD-L1 in PD-L1 humanized mice was confirmed with flow cytometry. Plasma concentrations of KN035 at different dosages at different time points were detected using an enzyme-linked immunosorbent assay. PD-L1 humanized mice were allocated into 4 groups: sham, cecal ligation and puncture (CLP), isotype (isotype+CLP), and PD-L1 (KN035+CLP). The 7-day survival rate was observed to investigate outcomes in CLP mice. Disease severity was assessed with histopathological scoring of mice lungs and livers. Immune status was assessed based on cell apoptosis in the spleen and bacterial clearance. RESULTS PD-L1 levels were significantly elevated in peripheral lymphocytes, monocytes, and neutrophils after CLP surgery. Blood concentrations of KN035 showed that 2.5 mg/kg had potential to be an ideal dosage for KN035 therapy. Survival analysis demonstrated that KN035 was associated with significantly reduced mortality on Day 7 after surgery (P=0.0083). The histopathological tests showed that KN035 alleviated sepsis-induced injury in the lungs and liver. KN035 reduced the number of apoptotic cells in the spleen and almost eliminated bacterial colonies in the peritoneal lavage fluid from the CLP mice. CONCLUSIONS KN035, an anti-PD-L1 antibody, can improve the rate of survival in CLP mice and alleviate sepsis-induced apoptosis in the spleen.

A novel ultrasound-guided mouse model of sudden cardiac arrest

AIM

Mouse models of sudden cardiac arrest are limited by challenges with surgical technique and obtaining reliable venous access. To overcome this limitation, we sought to develop a simplified method in the mouse that uses ultrasound-guided injection of potassium chloride directly into the heart.

METHODS

Potassium chloride was delivered directly into the left ventricular cavity under ultrasound guidance in intubated mice, resulting in immediate asystole. Mice were resuscitated with injection of epinephrine and manual chest compressions and evaluated for survival, body temperature, cardiac function, kidney damage, and diffuse tissue injury.

RESULTS

The direct injection sudden cardiac arrest model causes rapid asystole with high surgical survival rates and short surgical duration. Sudden cardiac arrest mice with 8-min of asystole have significant cardiac dysfunction at 24 hours and high lethality within the first seven days, where after cardiac function begins to improve. Sudden cardiac arrest mice have secondary organ damage, including significant kidney injury but no significant change to neurologic function.

CONCLUSIONS

Ultrasound-guided direct injection of potassium chloride allows for rapid and reliable cardiac arrest in the mouse that mirrors human pathology without the need for intravenous access. This technique will improve investigators' ability to study the mechanisms underlying post-arrest changes in a mouse model.

Butorphanol protects PC12 cells against OGD/R-induced inflammation and apoptosis

The aim of the present study was to examine the effects of butorphanol on neural injury in an oxygen glucose deprivation/reoxygenation (OGD/R) model using PC12 cells, and to investigate whether mitochondrial apoptosis was involved in these effects. To establish the OGD/R model, PC12 cells were cultured under hypoxia and low glucose conditions. Expression levels of inflammatory cytokines were evaluated by detecting the levels of tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and monocyte chemoattractant protein-1. Oxidative stress was evaluated by measuring the levels of reactive oxygen species, lactate dehydrogenase activity and myeloperoxidase concentration. Apoptosis, protein expression and cell viability were determined by flow cytometry, western blotting and by using a Cell Counting Kit-8, respectively. Compared with the control group, cell viability, expression of inflammatory factors and oxidative stress were all decreased in the OGD/R group. All the above changes could be mitigated by treatment with butorphanol. In addition, butorphanol treatment resulted in a significant upregulation of Bax, and downregulation of Bcl-2, activated caspase-3, caspase-9 and poly ADP-ribose polymerase, increased the expression of X-linked inhibitor of apoptosis protein and enhanced ATP activity. To conclude, these results suggested that the protective effects of butorphanol are associated with the inhibition of OGD/R-induced inflammation and apoptosis injury, and may be partially associated with the inhibition of mitochondrial apoptosis.

Effects of Standard and Sustained-release Buprenorphine on the Minimum Alveolar Concentration of Isoflurane in C57BL/6 Mice

Both standard and sustained-release injectable formulations of buprenorphine (Bup and BupSR, respectively) are used as preemptive analgesics, potentially affecting gas anesthetic requirements. This study tested the effects of Bup and BupSR on isoflurane requirements and confirmed that buprenorphine could reduce isoflurane requirements during a laparotomy in mice. We hypothesized that both Bup and BupSR would significantly decrease the required minimum alveolar concentration (MAC) of isoflurane. C57BL/6 mice received either isotonic crystalloid fluid (control), Bup (0.1 mg/kg), or BupSR (1.2 mg/kg) subcutaneously 10 min prior to the induction of anesthesia. Each anesthetized mouse was tested at 2 isoflurane concentrations. A 300-g noxious stimulus was applied at each isoflurane concentration, alternating between hindfeet. In addition, a subset of mice underwent terminal laparotomy or 60 min of anesthesia after injection with Bup, BupSR, or saline to ensure an appropriate surgical plane of anesthesia. Mice were maintained at the lowest isoflurane concentration that resulted in 100% of mice at a surgical plane from the aforementioned MAC experiments (control, 2.0%; Bup and BupSR, 1.7%). Analysis showed that both Bup and BupSR significantly decreased isoflurane requirements by 25.5% and 14.4%, respectively. The isoflurane MAC for the control injection was 1.80% ± 0.09%; whereas Bup and BupSR decreased MAC to 1.34% ± 0.08% and 1.54% ± 0.09%, respectively. Sex was not a significantly different between the injection groups during MAC determination. All of the mice that underwent surgery achieved a surgical plane of anesthesia on the prescribed regimen and recovered normally after discontinuation of isoflurane. Lastly, heart and respiratory rates did not differ between mice that underwent surgery and those that were anesthetized only. Bup and BupSR are MAC-sparing in male and female C57BL/6 mice and can be used for effective multimodal anesthesia.

Edaravone at high concentrations attenuates cognitive dysfunctions induced by abdominal surgery under general anesthesia in aged mice

Postoperative cognitive dysfunction (POCD) is a common neurological disease affecting the elderly patients after surgery. Unfortunately, no effective treatment for this disease has been discovered. Edaravone, a clinical-used free radical scavenger, at 3 mg/kg has been reported to prevent neuroinflammation induced by the combination of surgery and lipopolysaccharide in adult rodents. However, we found that edaravone at such low concentration could not inhibit POCD in aged mice. Instead, edaravone at 33.2 mg/kg significantly prevented recognition and spatial cognitive dysfunctions in 14 month aged mice after abdominal surgery under general anesthesia with isoflurane. Furthermore, edaravone significantly prevented the increase of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) induced by abdominal surgery in aged mice. Edaravone could also decrease glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule-1 (Iba-1) positive areas in the hippocampal regions of surgery mice, suggesting that edaravone might inhibit surgery-induced over-activation of microglia and astrocytes. Moreover, edaravone substantially increased the expression of PSD-95 and pSer9-glycogen synthase kinase-3β (pSer9-GSK3β) as demonstrated by Western blotting assay. Furthermore, the activity of acetylcholinesterase (AChE) is decreased in the mice in edaravone group. All these results suggested that edaravone at high concentrations could inhibit surgery-induced cognitive impairments in aged animals, possibly via the attenuation of neuroinflammation, the increase of synaptic proteins, and the elevation of cholinergic transmission, providing a further support that edaravone might be developed as a treatment of POCD.

New evidence for refinement of anesthetic choice in procedures preceding the forced swimming test and the elevated plus-maze

Previous studies indicated that some general anesthetics induce long-term antidepressant and/or anxiolytic-like effects. This raises the concern about the use of anesthesia in surgeries that precede psychopharmacological tests, since it may be a potential bias on results depending on the experimental design used. Thus, we evaluated whether general anesthetics used in surgeries preceding psychopharmacological tests would affect rats behavior in tests predictive of antidepressant or anxiolytic-like effects. We tested if a single exposure to sub-anesthetic or anesthetic doses of tribromoethanol, chloral hydrate, thiopental or isoflurane would change rats behavior in the forced swimming test (FST) or in the elevated plus-maze (EPM) test, at 2 h or 7 days after their administration. We also evaluated whether prior anesthesia would interfere in the detection of the antidepressant-like effect of imipramine or the anxiolytic-like effect of diazepam. Previous anesthesia with the aforementioned anesthetics did not change rats behaviors in FST per se nor it changed the antidepressant-like effect induced by imipramine treatment. Rats previously anesthetized with tribromoethanol or chloral hydrate exhibited, respectively, anxiogenic-like and anxiolytic-like behaviors in the EPM. Prior anesthesia with thiopental or isoflurane did not produce any per se effect in rats behaviors in the EPM nor disturbed the anxiolytic-like effect of diazepam. Our results suggest that, in our experimental conditions, tribromoethanol and chloral hydrate are improper anesthetics for surgeries that precede behavioral analysis in the EPM. Isoflurane or thiopental may be suitable for anesthesia before evaluation in the EPM or in the FST.

Different sensitivity to the suppressive effects of isoflurane anesthesia on cardiorespiratory function in SHR/Izm, WKY/Izm, and Crl:CD (SD) rats

Isoflurane is a widely used anesthetic, but its effects with increase in inspired concentration on cardiovascular function have not yet been clarified in rodents. Additionally, there are only a few studies comparing isoflurane-induced cardiorespiratory effects between rat strains. Thus, we investigated the differences in cardiorespiratory responsiveness to increasing concentration of inspired isoflurane in SHR/Izm, WKY/Izm and Crl:CD (SD) rats, by increasing the setting values of vaporizer's dial indicator. The rats were anesthetized with 1.5% isoflurane, and electrocardiograms, blood pressure, and respiratory rate were recorded simultaneously. Thereafter, the inspired concentration was increased stepwise to 2%, 3%, 4%, and 5%, and cardiorespiratory parameters were obtained at each concentration. Under anesthesia at more than 4%, although prolongation of the RR and PR intervals was observed in all strains, shortening of the QT_C interval was found only in SHR/Izm rats. From frequency domain analysis of heart rate variability, an increase in LF/HF ratio and a decrease of HF components were observed in SHR/Izm and WKY/Izm rats, respectively, with 5% isoflurane anesthesia. Blood pressure and heart rate were remarkably reduced in SHR/Izm rats at higher concentrations, whereas the reduction was smallest in WKY/Izm rats among the three strains examined. Respiratory rate was inspired concentration-dependently decreased in all strains. These results suggested that SHR/Izm rats are more sensitive to suppressive effects of isoflurane anesthesia on cardiovascular function among these rat strains.

Combining isoflurane anesthesia with midazolam and butorphanol in rats

Representative inhalant anesthetic agent, isoflurane is commonly used during surgery in rats. However, isoflurane mediates relatively strong respiratory depression. In human and veterinary medicine, sedatives and analgesics are co-administered to complement the anesthetic action of inhalant anesthesia. The present study aimed to establish the novel balanced anesthesia that combines midazolam and butorphanol with isoflurane (MBI) in rats. Male Sprague Dawley rats were divided into 2 groups, and administered either isoflurane monoanesthesia or isoflurane with midazolam (2.5 mg/kg, ip) and butorphanol (2.0 mg/kg, ip). The minimum alveolar concentration (MAC) in each group was evaluated. Induction and recovery times were measured in each group. Adverse reactions during induction were also recorded. In each group, vital signs were assessed for 1 h under 1.5×MAC of isoflurane. Instability of vital signs was assessed under each anesthesia by calculating coefficient of variance. Compared with isoflurane monoanesthesia, MBI anesthesia caused 32% MAC reduction (isoflurane monoanesthesia: 1.30 ± 0.09%, MBI 0.87 ± 0.08%, P<0.05). MB premedication mediated smooth sedating action with low incidence of adverse reactions such as urination and defecation. Isoflurane monoanesthsesia remarkably decreased respiratory rate and saturation O₂ (SPO₂). In contrast, MBI anesthesia resulted in a relatively stable respiratory rate without decreases in SPO₂ during the anesthetic period. In summary, MB premedication is effective for attenuating respiratory depression induced by isoflurane, and achieving smooth induction. This anesthetic protocol serves as a novel option for appropriate anesthesia in rats.