Anesthesia for Echocardiography and Magnetic Resonance Imaging in the African Clawed Frog (Xenopus laevis)

This report describes an anesthesia technique that we used to study cardiovascular anatomy and physiology with echocardiography and cardiac magnetic resonance (CMR) in 46 African clawed frogs (Xenopus laevis) (n = 24 for electrocardiography and n = 22 for CMR). For administration of anesthesia, 3 holding tanks, one each for transportation, sedation, and recovery, were filled with filtered water, with 0.05% buffered tricaine methasulfonate solution (MS-222) added into the sedation tank. Fifteen minutes after the frog was placed in the sedation tank, a paper towel was soaked in MS-222 solution, and the frog was placed in a supine position and rolled 3 to 4 times in the soaked paper with the head and legs exposed. Vital signs were monitored and recorded throughout the procedure. After imagining, frogs were unrolled from the paper towel, placed in the recovery tank, and later returned to their home tank. Monitoring was discontinued when the frogs resumed typical activity. No mortality or complications were observed in frogs that underwent this procedure. Mean duration ±1 SD of anesthesia induction was 12 ± 5 min in the echocardiography group and 14 ± 6 min in the CMR group. The mean duration of anesthesia maintenance was 60 ± 18 min in the echocardiography group and 118 ± 37 min in the CMR group. An additional dose of anesthesia was necessary during maintenance for 9 of 24 (37%) frogs in the echocardiography group and 6 of 22 (27%) frogs in the CMR group. At the end of the procedure, the mean oxygen saturation was 66 ± 9% in the echocardiography group and 85 ± 6% in the CMR group, and heart rate was 48 ± 13 beats/min in the echocardiography group and 42 ± 7 beats/min in the CMR group. We conclude that the anesthesia technique of immersion in MS-222 is suitable for performing echocardiography and CMR imaging in this species without complications.

Characteristic pancreatic and splenic immune cell infiltration patterns in mouse acute pancreatitis

BACKGROUND

A systemic evaluation of immune cell infiltration patterns in experimental acute pancreatitis (AP) is lacking. Using multi-dimensional flow cytometry, this study profiled infiltrating immune cell types in multiple AP mouse models.

METHODS

Three AP models were generated in C57BL/6 mice via cerulein (CAE) injection, alcohol and palmitoleic acid (EtOH + POA) injection, and alcohol diet feeding and cerulein (EtOH + CAE) injection. Primary pancreatic cells and splenocytes were prepared, and multi-dimensional flow cytometry was performed and analyzed by manual gating and computerized PhenoGraph, followed by visualization with t-distributed stochastic neighbor embedding (t-SNE).

RESULTS

CAE treatment induced a time-dependent increase of major innate immune cells and a decrease of follicular B cells, and T^CD4+ cells and the subtypes in the pancreas, whereas elicited a reversed pattern in the spleen. EtOH + POA treatment resulted in weaker effects than CAE treatment. EtOH feeding enhanced CAE-induced amylase secretion, but unexpectedly attenuated CAE-induced immune cell regulation. In comparison with manual gating analysis, computerized analysis demonstrated a remarkable time efficiency and reproducibility on the innate immune cells and B cells.

CONCLUSIONS

The reverse pattern of increased innate and decreased adaptive immune cells was consistent in the pancreas in CAE and EtOH + POA treatments. Alcohol feeding opposed the CAE effect on immune cell regulation. Together, the immune profiling approach utilized in this study provides a better understanding of overall immune responses in AP, which may facilitate the identification of intervention windows and new therapeutic strategies. Computerized analysis is superior to manual gating by dramatically reducing analysis time.

Accuracy of 5 Point-of-Care Glucometers in C57BL/6J Mice

Despite few published studies that assess the accuracy of glucometers in laboratory animals, glucometers are commonly used in animal research. We set out to determine the accuracy of 5 point-of-care glucometers (POCG) when used to evaluate murine whole blood, plasma, and serum samples. The POCG tested included one veterinary device (POCG A) and 4 humanuse instruments (POCG B through E). Whole blood, plasma, and serum samples from 50 female C57BL/6J mice were analyzed on all POCG, and serum was analyzed on a reference biochemical analyzer. The mean blood glucose concentration (BGC) measured in whole blood by using POCG A was greater than that on the biochemical analyzer, whereas the mean BGC in whole blood according to POCG B through E did not differ significantly from that on the biochemical analyzer. Mean BGC in plasma and serum did not differ between POCG B and E and the biochemical analyzer, whereas the plasma and serum BGC values from POCG C and D were greater than the mean BGC from the biochemical analyzer. The accuracy of each POCG for each sample type was evaluated by analyzing mean differences, correlations, and Bland-Altman graphs. We found that the 4 human-use POCG are appropriate for use with whole blood from female C57BL/6J mice, whereas only 2 of the evaluated POCG were sufficiently accurate for use with plasma or serum.

Therapeutic effect of Lactobacillus reuteri DSM 17938 on Treg-deficiency-induced autoimmunity (IPEX syndrome) via the inosine-adenosine 2A receptors

Regulatory T-cell (Treg) deficiency causes lethal, CD4+T cell-driven autoimmune diseases. Stem cell transplantation is used to treat these diseases, but this procedure is limited by the availability of a suitable donor. The intestinal microbiota drives host immune homeostasis by regulating the development of Treg, Th1 and Th2 cells. It is currently unclear if Treg-deficiency autoimmune disorders can be treated by targeting the enteric microbiota. Our aims are to determine the autoimmunity, gut microbiota, and plasma metabolomics affected by probiotic Lactobacillus reuteri DSM 17938 (LR), and to further identify the mechanism of modulated metabolite(s) in suppressing autoimmunity in Treg-deficient scurfy (SF) mice. We demonstrated that Foxp3+Treg deficiency results in gut microbial dysbiosis and autoimmunity over the lifespan of SF mouse. Remodeling microbiota with LR prolonged survival and reduced multi-organ inflammation in SF mice. LR changed the metabolomics profile disrupted by Treg-deficiency with a major effect of restoring levels of the purine metabolite inosine. Feeding inosine itself prolonged life and inhibited multi-organ inflammation by reducing Th1/Th2 cells and their associated cytokines. Mechanistically, the inhibition of inosine on the differentiation of Th1 and Th2 cells in vitro depended on adenosine A2A receptors. Both A2A receptor specific antagonist or genetically knockout A2A to SF mice reversed the anti-inflammatory effects of both inosine and LR in vivo. In conclusions, A2A receptors mediate a substantial protective effect of inosine and LR. The LR-modulated-microbiota-inosine-A2A axis might represent a potential avenue for combatting autoimmune diseases mediated by Treg dysfunction.

Resetting microbiota by Lactobacillus reuteri inhibits T reg deficiency-induced autoimmunity via adenosine A2A receptors

He et al. show that T reg deficiency markedly induces autoimmunity and shifts gut microbiota. Remodeling microbiota by Lactobacillus reuteri was found to inhibit autoimmunity via the metabolite inosine, which interacts with the adenosine A_2A receptor. This finding establishes a link between the gut microbiota, A_2A receptors, and autoimmunity induced by T reg cell deficiency.

Regulatory T (T reg) cell deficiency causes lethal, CD4⁺ T cell–driven autoimmune diseases. Stem cell transplantation is used to treat these diseases, but this procedure is limited by the availability of a suitable donor. The intestinal microbiota drives host immune homeostasis by regulating the differentiation and expansion of T reg, Th1, and Th2 cells. It is currently unclear if T reg cell deficiency–mediated autoimmune disorders can be treated by targeting the enteric microbiota. Here, we demonstrate that Foxp3⁺ T reg cell deficiency results in gut microbial dysbiosis and autoimmunity over the lifespan of scurfy (SF) mouse. Remodeling microbiota with Lactobacillus reuteri prolonged survival and reduced multiorgan inflammation in SF mice. L. reuteri changed the metabolomic profile disrupted by T reg cell deficiency, and a major effect was to restore levels of the purine metabolite inosine. Feeding inosine itself prolonged life and inhibited multiorgan inflammation by reducing Th1/Th2 cells and their associated cytokines. Mechanistically, the inhibition of inosine on the differentiation of Th1 and Th2 cells in vitro depended on adenosine A_2A receptors, which were also required for the efficacy of inosine and of L. reuteri in vivo. These results reveal that the microbiota–inosine–A_2A receptor axis might represent a potential avenue for combatting autoimmune diseases mediated by T reg cell dysfunction.

Concurrent nonindependent fixed-ratio schedules of alcohol self-administration: Effects of schedule size on choice

Choice behavior was studied under concurrent nonindependent fixed‐ratio fixed‐ratio (nFR) schedules of reinforcement, as these schedules result in frequent changeover responses. With these schedules, responses on either operandum count toward the completion of the ratio requirements of both schedules. Five monkeys were subjects, and two pairs of liquid reinforcers were concurrently available: 16% (w/v) and 0% ethanol or 16% and 8% ethanol. For each pair of reinforcers, the nFR sizes were systematically altered across sessions while keeping the schedule size equal for both liquids. Responding varied as a function of reinforcer pair and nFR size. With the 16% and 0% pair, higher response rates were maintained by 16% and were an inverted U‐shape function of nFR size. With 16% and 8%, a greater number of responses initially occurred on the schedule that delivered 8% ethanol. However, as nFR size increased, preference reversed such that responses that delivered 16% ethanol were greater. When the nFR size was subsequently decreased, preference reverted back to 8%. Number of responses emitted per delivery was a dependent variable and, in behavioral economic terms, was the price paid for each liquid delivery. With 16% and 0%, changeover responses initially increased and then decreased as schedule size became larger. In contrast, with the 16% and 8% pair, changeover responses increased directly with schedule size. Responding under nFR schedules is sensitive to differences in reinforcer magnitude and demonstrates that relative reinforcing effects can change as a function of schedule size.

Effects of Environmental Enrichment on the Fertility and Fecundity of Zebrafish (Danio rerio)

Zebrafish (Danio rerio) are a popular vertebrate model in biomedical research, but information describing the effects of environmental enrichment on fertility and fecundity of zebrafish is sparse. In the current study, 18 breeding pairs were placed in divided 1.5-L breeding tanks containing 1 of 3 enrichment conditions: plastic grass (n = 6), plastic leaves (n = 6), or no enrichment (n = 6, control). The pairs were allowed to spawn for 3 h the next day, after which eggs were counted and breeding pairs were returned to holding tanks for use in subsequent sessions. Spawning sessions were repeated at 7-d intervals until the completion of 9 trials, with pairs rotating to a different condition at each interval. Total egg count (mean ± SEM) after 3 h was greater for zebrafish spawning in the grass environment (48.0 ± 7.7 eggs) than in the leaf or control environments (29.4 ± 5.3 and 20.4 ± 3.7 eggs, respectively). An interaction emerged between enrichment type and the age of the spawning pair on the number of fry at 6 d postfertilization (dpf). Initially, more fry were obtained from 110- and 160-dpf pairs with the grass enrichment, but from 173- and 180-dpf pairs there were more obtained with leaf enrichment than grass. A separate experiment showed that enrichment type did not have an effect on fry survivability. Overall, our data indicates that, under certain conditions, zebrafish fertility and fecundity are greater in a breeding tank containing environmental enrichment than in a bare tank.

Direct relation between etonitazene dose and response rate: responding under a single FI per session

Response-contingent injections of etonitazene (ETZ) have been shown to reinforce rats' lever pressing behavior. The objective of the present study was to determine the relation between response rate and ETZ dose when ETZ was administered subcutaneously once per session by the experimenter contingent upon completion of a 10-min fixed-interval (FI) schedule. When injections of the saline vehicle replaced drug injections, response rates dropped to low levels; rates subsequently increased above saline levels when drug injections were reintroduced, demonstrating that ETZ was serving as a reinforcer. A range of ETZ doses (0.01, 0.1, 1, 5.7, and 10 microg/kg) was administered subcutaneously to six rats, resulting in response rates that were directly related to drug dose. These findings are consistent with other studies that have found an increase in reinforcing effects with increases in drug dose. Thus, studies in which drug is administered once per session may be used to measure the reinforcing effects of drugs directly from rate measures, as the response rate in these studies is unaffected by satiation or direct drug effects.

Relation between choice of ethanol concentration and response rates under progressive- and fixed-ratio schedules: studies with rhesus monkeys

RATIONALE

A fundamental problem in the study of drugs as reinforcers is the evaluation of a drug's relative reinforcing effects and changes in such effects. Relative reinforcing effects can be measured by determining the preference for one drug dose relative to another drug dose. However, in IV drug self-administration studies technical limitations make direct comparisons between drug doses difficult. An alternative procedure is to measure the relative persistence of behavior across increases in schedule size.

OBJECTIVE

To develop a more rapid method to measure the relative persistence of behavior. Instead of increasing the schedule size across sessions, schedule size was increased within sessions by use of a progressive-ratio schedule (PR).

METHODS

Male rhesus monkeys orally self-administered ethanol during daily 3-h sessions. At each concentration responding was measured with fixed-ratio (FR) 8 schedules to obtain baseline values. Subsequently behavior was studied with a PR schedule. Relative persistence of behavior was calculated by dividing the mean response rate under the PR schedule by the mean response rate under the FR8 schedules. To compare these findings with results of choice between concentrations, monkeys were given concurrent access to pairs of ethanol concentrations.

RESULTS

The relative persistence of behavior increased with increases in drug concentration. When two concentrations were concurrently available, the higher concentration maintained higher response rates.

CONCLUSIONS

The relative persistence of behavior can be efficiently measured by dividing the response rate under the PR schedule by the response rate under the FR schedule. Measures of relative persistence corresponded well with measures of choice and show that relative reinforcing effects increase as dose increases.

Relative reinforcing effects of different benzodiazepine doses for rhesus monkeys

The relative reinforcing effects of different doses of benzodiazepines were determined by giving rhesus monkeys concurrent access to different diazepam and midazolam concentrations. For each monkey a dose response function was obtained using three drug concentrations: low (L), intermediate (I), and high (H). The benzodiazepine and the water vehicle were concurrently available under independent fixed-ratio (FR) schedules. After establishing that each concentration was a reinforcer in comparison to vehicle, relative preference for the different concentrations was examined by making pairs of concentrations concurrently available under independent FR schedules. Three pairs were studied (H vs. L, H vs. I, and I vs. L). With both drugs, higher concentrations maintained greater response rates than lower concentrations. Thus, relative reinforcing effects increased with dose. These findings are similar to those obtained with other reinforcing drugs and provide further evidence that benzodiazepines share significant characteristics with other drug reinforcers. Importantly, absolute response rates (responses per session) obtained when only one drug dose was present were not reliably predictive of subsequent preferences for the dose. Both benzodiazepines served as effective reinforcers in that consistent levels of responding were maintained across doses and above vehicle levels under concurrent FR 32 schedules. As with other reinforcing drugs, the reinforcing effects of benzodiazepines increase with increases in dose over a broad range of values.

Orally delivered alprazolam, diazepam, and triazolam as reinforcers in rhesus monkeys

RATIONALE

Benzodiazepines are among the most frequently prescribed drugs and are usually taken by mouth. However, there have been few studies of oral self-administration of these drugs, and the results of IV self-administration studies indicate that benzodiazepines are modest reinforcers.

OBJECTIVES

To determine if orally delivered alprazolam, diazepam, and triazolam could serve as reinforcers for rhesus monkeys, and to determine some of the conditions under which benzodiazepine reinforced behavior occurs.

METHODS

Diazepam or midazolam was initially established as a reinforcer by a fading procedure whereby increasing concentrations were added to a 1 or 2% ethanol solution, and subsequently the ethanol concentration was decreased in steps to zero. Diazepam- and midazolam-reinforced responding persisted in the absence of ethanol. Triazolam and alprazolam served as reinforcers when substituted for diazepam or midazolam.

RESULTS

Alprazolam, diazepam, and triazolam served as effective reinforcers across a wide range of concentrations and under fixed-ratio sizes of 16 and 32. Rates of responding were usually far higher than that for the concurrently available vehicle, water. Drug intake (mg drug/kg body weight) generally increased with increases in drug concentration. When large drug amounts were consumed, signs of intoxication were observed.

CONCLUSIONS

In contrast to reports of low response rates and weakly maintained behavior, the present results show that the three benzodiazepines can serve as effective reinforcers.

Reinforcing effects of contingently administered subcutaneous injections of etonitazene in rats

RATIONALE

Response-contingent injections of opioids have been shown to control behavior in various species.

OBJECTIVE

To determine whether s.c. injections of etonitazene (ETZ) could maintain behavior in rats when administered under a single fixed-interval schedule.

METHODS

Rats were trained to lever press for eight 45-mg food pellets under a single fixed-interval (FI) 10-min schedule of reinforcement: following passage of the 10-min interval, each lever press resulted in a pellet delivery until eight pellets were obtained. Delivery of the reinforcer was signaled by a change in visual stimulus conditions. Once stable responding for the food pellets under the FI 10-min schedule was established, a s.c. injection of 3.2 micrograms/kg ETZ was administered to the rat by the investigator following schedule completion and delivery of the food pellets. After receiving the drug injection, rats were returned to the experimental chamber for 30 min and exposed to the same stimulus conditions that accompanied food reinforcement. Across sessions, the number of food pellets was decreased until rats were responding solely for the drug.

RESULTS

Responding for the s.c. administered drug stabilized and persisted across sessions. When saline vehicle injections were substituted for the drug injections, responses diminished across sessions to levels below that of the drug baseline. Subsequent alternating blocks of ETZ and vehicle injections produced respective increases and decreases in responding.

CONCLUSION

This study demonstrates that response-contingent s.c. injections of a drug can control behavior in rats, systematically replicating a previous experiment that used the i.p. route. Since all pertinent operant behavior is emitted prior to the administration of drug, this procedure can be used for testing the reinforcing effects of a drug without interference from any direct (rate-altering) drug effects. The present findings also extend the conditions under which drugs of abuse may reinforce behavior.

Lever-press responding maintained by contingent intraperitoneal administration of etonitazene in Long Evans hooded rats

Lever pressing maintained by intraperitoneal (i.p.) injections of etonitazene was established in five Long Evans hooded rats. Each training session consisted of an 8-min fixed interval (FI) during which lever pressing was maintained by food pellets delivered at the end of the interval. Food delivery was accompanied by illumination of stimulus lights in the chamber. Every 20th response during the 8 min interval also produced a brief illumination of the stimulus lights (FI 8 min (FR 20:S)). Administration of etonitazene was then introduced. Immediately following food delivery, the rat received an i.p. drug injection and was returned to the operant chamber for 30 min. During this confinement, the stimulus lights remained illuminated. This procedure resembles conditioned place preference in that an environment is paired with the effects of an investigator-delivered drug. When food pellet delivery subsequently was discontinued, responding persisted when followed by drug, but not saline, administration. Alternating blocks of sessions with administration of etonitazene (6.0-9.0 microg/kg) or saline produced corresponding increases or decreases in responding. These results indicate that etonitazene can function as a reinforcer when administered to rats by the i.p. route, and thus extend the range of conditions under which drug reinforcement can be investigated.