This work was supported by the National Institutes of Health grant R01DK117872 awarded to OO and the Larry L Hillblom Foundation Fellowship awarded to RCZ.

All procedures involving animal subjects have been approved by the Institutional Animal Care and Use Committee (IACUC) at the University of California, San Diego.
1. Making the drug-peanut butter pellet
<ol>
	<li>Calculate the amount of drug needed to make the desired dose of drug in a pellet of peanut butter and scale to the size of the batch required for an experiment. Importantly, pellets can be kept at -80 &#176;C, depending on drug stability.</li>
	<li>Pulverize the drug tablets using a mortar and pestle.</li>
	<li>Weigh the calculated amount peanut butter required by placing it in a weigh boat on a tared scale.</li>
	<li>Place the peanut butter over a beaker of warm water until melted.</li>
	<li>Add the required amount of pulverized drug into the melted peanut and mix thoroughly.</li>
	<li>Allow the drug-peanut butter mixture to cool so that it can be easily placed into the rubber molds.</li>
	<li>Place the peanut butter-drug mix into a mold. The one used here is a rubber corticosterone pellet mold and creates approximately ~100 mg peanut butter pellets. Adjustment of the ratio of drug to peanut butter may be necessary to ensure palatability.</li>
	<li>Repeat these steps with peanut butter alone to make placebo pellets.</li>
	<li>Freeze the mold at -20 &#176;C or -80 &#176;C (depending on drug stability) to allow the peanut butter to harden until use.</li>
</ol>
2. Mouse setup
<ol>
	<li>Singly house mice in standard mouse cages. Line with highly absorbent paper bedding and enrichment, including paper towels and housing dome. This paper bedding facilitates accurate food intake measurements by allowing quantification of spilled food from feces and bedding. 
	NOTE: ENsure IACUC approval for singly housing mice has been obtained.</li>
	<li>Provide ad libitum food and water and allow the mice to acclimate to the housing for approximately 3 days.</li>
</ol>
3. Training to self-dosing of drug-peanut butter
<ol>
	<li>Plan and select the optimum time of the day for the drug administration.</li>
	<li>Fast the mice for 24 hours and ensure that IACUC approval has been received for the chosen fasting duration.</li>
	<li>Take the mold out the freezer, let the rubber mold soften so that the pellets can be easily extruded out of the mold. All training can be completed using placebo control pellets.</li>
	<li>Place a placebo control peanut butter pellet on the wall of the cage approximately 1.5 inches from the base. On the first day, it may take approximately 1 hour for the mouse to consume the peanut butter pellet due to novelty.</li>
	<li>After the training session provide ad libitum access to food and water.</li>
	<li>On the following day, place the peanut butter pellet on the wall of the cage in the same location for further training on non-fasted mice.</li>
	<li>Repeat the training in fed mice for approximately 3 days. The time taken to consume the peanut butter will be less than 30 minutes by the third day of training.</li>
</ol>
4. Experiment
<ol>
	<li>Randomize mice to treatment groups based on body weight so the groups have the same average body weight before treatment.</li>
	<li>Plan to administer the peanut butter pills (treatment or placebo) to the mice at the same time they were trained to receive the peanut butter pellets.</li>
	<li>Weigh the food and mouse and record the values.</li>
	<li>Ensure that the peanut butter pills (treatment or placebo) are placed at the same location in the cage as established during training.</li>
	<li>Continue the dosing procedure daily for the duration of the experiment.</li>
</ol>

<ol><li>de Meijer, V. E., Le, H. D., Meisel, J. A., Puder, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Repetitive+orogastric+gavage+affects+the+phenotype+of+diet-induced+obese+mice%5BTitle%5D)+AND+%22Physiology+and+Behavior%22%5BJournal%5D)">Repetitive orogastric gavage affects the phenotype of diet-induced obese mice.</a> Physiology and Behavior. 100 (4), 387-393 (2010).</li>
<li>Perez-Gomez, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+phenotypic+Caenorhabditis+elegans+screen+identifies+a+selective+suppressor+of+antipsychotic-induced+hyperphagia%5BTitle%5D)+AND+%22Nature+Communications%22%5BJournal%5D)">A phenotypic Caenorhabditis elegans screen identifies a selective suppressor of antipsychotic-induced hyperphagia.</a> Nature Communications. 9 (1), 5272(2018).</li>
<li>Corbett, A., McGowin, A., Sieber, S., Flannery, T., Sibbitt, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+method+for+reliable+voluntary+oral+administration+of+a+fixed+dosage+%28mg%2Fkg%29+of+chronic+daily+medication+to+rats%5BTitle%5D)+AND+%22Laboratory+Animal%22%5BJournal%5D)">A method for reliable voluntary oral administration of a fixed dosage (mg/kg) of chronic daily medication to rats.</a> Laboratory Animal. 46 (4), 318-324 (2012).</li>
<li>Teixeira-Santos, L., Albino-Teixeira, A., Pinho, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((An+alternative+method+for+oral+drug+administration+by+voluntary+intake+in+male+and+female+mice%5BTitle%5D)+AND+%22Laboratory+Animal%22%5BJournal%5D)">An alternative method for oral drug administration by voluntary intake in male and female mice.</a> Laboratory Animal. 55 (1), 76-80 (2021).</li>
<li>Zhang, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Method+for+voluntary+oral+administration+of+drugs+in+mice%5BTitle%5D)+AND+%22STAR+Protocols%22%5BJournal%5D)">Method for voluntary oral administration of drugs in mice.</a> STAR Protocols. 2 (1), 100330(2021).</li>
<li>Cope, M. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Risperidone+alters+food+intake%2C+core+body+temperature%2C+and+locomotor+activity+in+mice%5BTitle%5D)+AND+%22Physiology+and+Behaviour%22%5BJournal%5D)">Risperidone alters food intake, core body temperature, and locomotor activity in mice.</a> Physiology and Behaviour. 96 (3), 457-463 (2009).</li>
<li>Barton, B. B., Segger, F., Fischer, K., Obermeier, M., Musil, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Update+on+weight-gain+caused+by+antipsychotics%3A+a+systematic+review+and+meta-analysis%5BTitle%5D)+AND+%22Expert+Opinion+in+Drug+Safety%22%5BJournal%5D)">Update on weight-gain caused by antipsychotics: a systematic review and meta-analysis.</a> Expert Opinion in Drug Safety. 19 (3), 295-314 (2020).</li>
<li>Cope, M. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Antipsychotic+drug-induced+weight+gain%3A+development+of+an+animal+model%5BTitle%5D)+AND+%22International+Journal+of+Obesity%22%5BJournal%5D)">Antipsychotic drug-induced weight gain: development of an animal model.</a> International Journal of Obesity. 29 (6), 607-614 (2005).</li>
<li>Domecq, J. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Clinical+review%3A+Drugs+commonly+associated+with+weight+change%3A+a+systematic+review+and+meta-analysis%5BTitle%5D)+AND+%22Journal+of+Clinical+Endocrinology+and+Metabolism%22%5BJournal%5D)">Clinical review: Drugs commonly associated with weight change: a systematic review and meta-analysis.</a> Journal of Clinical Endocrinology and Metabolism. 100 (2), 363-370 (2015).</li>
<li>Wei, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dopamine+D2+receptor+signaling+modulates+pancreatic+beta+cell+circadian+rhythms%5BTitle%5D)+AND+%22Psychoneuroendocrinology%22%5BJournal%5D)">Dopamine D2 receptor signaling modulates pancreatic beta cell circadian rhythms.</a> Psychoneuroendocrinology. 113, 104551(2020).</li>
</ol>

The authors have no conflicts of interest to declare.

When conducting this protocol, it is important to be consistent with the accuracy of the measurements of food intake and body weight and the timing of drug administration throughout the study. While this self-administration method requires a significant training phase, this is particularly important to acclimate the mice to the novelty of the peanut butter and ensure mice consume the drug at the time given. Once established, it also offers great experimental flexibility and can be modified and adapted to deliver drugs at...

The goal of this method is to deliver drugs in mice via a non-invasive, minimally stressful procedure. Preclinical studies in mice often rely on stressful, invasive routes of drug administration that can have significant impacts on metabolic parameters. For example, repetitive daily oral gavage can significantly decrease caloric intake and weight gain in mice1. In addition, oral gavage can be technically challenging and has the potential to cause injuries. As an alternative, mice can self-administer compounds that are mixed in their food or dissolved in their drinking water 2. However, this approach has a major limitation, which is, it relies on the natural circadian timing of food or water intake. Furthermore, drug stability or solubility in water can be major issues when chronically delivered in this way. To overcome these limitations, drugs can be mixed with highly palatable foods, such as cookie dough 3, jelly 4,5 or peanut butter 6 to encourage self-administration in mice at a specified time. This approach has the advantage of facilitating drug delivery with minimal stress compared with an injection or daily gavage1. This procedure can be adapted to deliver a wide variety of drugs to mice. This protocol demonstrates the process of drug preparation, training, followed by drug delivery in highly palatable food. As an example, this method is used to administer the antipsychotic drug risperidone to C57BL/6J female mice. Risperidone is well known to have potent hyperphagic and weight gain effects in patients 7 that is well modelled in rodents 6,8. This system of administration facilitates a highly translational model that could be used to study a wide variety of drugs and their effects on pathways regulating food intake and body weight 9.

<table><tbody><tr><td>C57B6/J mice</td><td>Jackson Labs, Sacramento, CA, USA</td><td>664</td><td></td></tr><tr><td>corticosterone pellet mold</td><td>Ted Pella Inc, Redding, CA, USA</td><td>106A</td><td></td></tr><tr><td>Mouse igloo</td><td>VWR, Visalia, CA, USA</td><td>89067-850</td><td>cage enrichment</td></tr><tr><td>peanut butter</td><td>Jif Peanut Butter, Orrville, OH, USA</td><td></td><td>Creamy peanut butter</td></tr><tr><td>pestle and mortar</td><td>VWR, Visalia, CA, USA</td><td>470148-960</td><td></td></tr><tr><td>risperidone</td><td>Patriot Pharmaceuticals, Horsham, PA, USA</td><td>50458-593-50</td><td></td></tr><tr><td>rodent chow</td><td>LabDiet, St. Louis, MO, USA</td><td>5001</td><td></td></tr><tr><td>weigh boat</td><td>VWR, Visalia, CA, USA</td><td>10803-148</td><td></td></tr><tr><td>weighing scale</td><td>Mettler Toledo, Greifensee, Switzerland</td><td>MS104TS</td><td></td></tr><tr><td>Wypall paper X60</td><td>Kimberly-Clark, Corinth, MS, USA</td><td>34865-05</td><td>absorbent paper bedding</td></tr></tbody></table>

self-administration of drugs in mouse models of feeding and obesity

Preclinical studies in mice often rely on invasive protocols, such as injections or oral gavage, to deliver drugs. These stressful routes of administration have significant effects on important metabolic parameters including food intake and body weight. Although an attractive option to circumvent this is to compound the drug in rodent food or dissolve it in water, these approaches also have limitations as they are affected by drug stability at room temperature for extended periods of time, the drug's solubility in water, and that the dosing is highly dependent on timing of food or water intake. The constant availability of the drug also limits translational relevance on how drugs are administered to patients. To overcome these limitations, drugs can be mixed with highly palatable food, such as peanut butter, allowing mice to self-administer compounds. Mice reliably and reproducibly consume the drug/peanut butter pellet in a short time frame. This approach facilitates a delivery approach with minimal stress compared with an injection or gavage. This protocol demonstrates the approach of drug preparation, animal acclimatization to placebo delivery, and drug delivery. The implications of this approach are discussed in studies related to timing of drug administration and the circadian rhythm.

In the example presented here, peanut butter was used to deliver risperidone to mice daily for 14 days.
This study shows the chronic delivery of risperidone via this method facilitates highly reproducible increase in food intake and body weight compared with control (Figure 1a,b). In addition, this delivery method results in highly consistent data compared with alternative, more stressful delivery approaches such as intraperitoneal injections (<st...

Watch this Scientific Journal Video about Self-Administration of Drugs in Mouse Models of Feeding and Obesity at JoVE.com

Self-Administration of Drugs in Mouse Models of Feeding and Obesity

The overall goal of this procedure is to describe a method for self-administration of drugs that can be used in mouse models of feeding and obesity.

Preclinical studies in mice often rely on invasive protocols, such as injections or oral gavage, to deliver drugs. These stressful routes of ...

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4.4K Views.  University of California San Diego. The overall goal of this procedure is to describe a method for self-administration of drugs that can be used in mouse models of feeding and obesity. 

Video: Self-Administration of Drugs in Mouse Models of Feeding and Obesity

A Novel Procedure for Evaluating the Reinforcing Properties of Tastants in Laboratory Rats: Operant Intraoral Self-administration

This paper describes a novel method for studying the bio-behavioral basis of addiction to food. This method combines the surgical component of taste reactivity with the behavioral aspects of operant self-administration of drugs. Under very brief general anaesthesia, rats are implanted with an intraoral (IO) cannula that allows delivery of test solutions directly in the oral cavity. Animals are then tested in operant self-administration chambers whereby they can press a lever to receive IO infusions of test solutions. IO self-administration has several advantages over experimental procedures that involve drinking a solution from a spout&#160;or operant responding for solid pellets or solutions delivered in a receptacle. Here, we show that IO self-administration can be employed to study self-administration of high fructose corn syrup (HFCS). Rats were first tested for self-administration on a progressive ratio (PR) schedule, which assesses the maximum amount of operant behavior that will be emitted for different concentrations of HFCS (i.e.&#160;8%, 25%, and 50%). Following this test, rats self-administered these concentrations on a continuous schedule of reinforcement (i.e.&#160;one infusion for each lever press) for 10 consecutive days (1 session/day; each lasting 3 hr), and then they were retested on the PR schedule. On the continuous reinforcement schedule, rats took fewer infusions of higher concentrations, although the lowest concentration of HFCS (8%) maintained more variable self-administration. Furthermore, the PR tests revealed that 8% had lower reinforcing value than 25% and 50%. These results indicate that IO self-administration can be employed to study acquisition and maintenance of responding for sweet solutions. The sensitivity of the operant response to differences in concentration and schedule of reinforcement makes IO self-administration an ideal procedure to investigate the neurobiology of voluntary intake of sweets.

The current study evaluates a novel procedure for assessing the reinforcing effects of palatable solutions in laboratory rats: intraoral self-administration. To this end, operant responding (i.e.&#160;lever pressing) for intraoral infusions of sweet solutions at different concentrations was measured on continuous and progressive ratios schedules of reinforcement.

This paper describes a novel method for studying the bio-behavioral basis of addiction to food. This method combines the surgical component of taste ...

Behavior

Fat Preference: A Novel Model of Eating Behavior in Rats

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

Dietary fat content influences both energy intake and body fat composition in mammals. By examining rats&#8217; preference for high fat food in a series of choice experiments, it is possible to test genetic differences and pharmacological interventions on their preference for high fat food.

Obesity is a growing problem in the United States of America, with more than a third of the population classified as obese. One factor contributing to ...

Operant Sensation Seeking in the Mouse

Operant methods are powerful behavioral tools for the study of motivated behavior. These 'self-administration' methods have been used extensively in drug addiction research due to their high construct validity. Operant studies provide researchers a tool for preclinical investigation of several aspects of the addiction process. For example, mechanisms of acute reinforcement (both drug and non-drug) can be tested using pharmacological or genetic tools to determine the ability of a molecular target to influence self-administration behavior1-6. Additionally, drug or food seeking behaviors can be studied in the absence of the primary reinforcer, and the ability of pharmacological compounds to disrupt this process is a preclinical model for discovery of molecular targets and compounds that may be useful for the treatment of addiction3,7-9. One problem with performing intravenous drug self-administration studies in the mouse is the technical difficulty of maintaining catheter patency. Attrition rates in these experiments are high and can reach 40% or higher10-15. Another general problem with drug self-administration is discerning which pharmacologically-induced effects of the reinforcer produce specific behaviors. For example, measurement of the reinforcing and neurological effects of psychostimulants can be confounded by their psychomotor effects. Operant methods using food reinforcement can avoid these pitfalls, although their utility in studying drug addiction is limited by the fact that some manipulations that alter drug self-administration have a minimal impact on food self-administration. For example, mesolimbic dopamine lesion or knockout of the D1 dopamine receptor reduce cocaine self-administration without having a significant impact on food self-administration 12,16. 
Sensory stimuli have been described for their ability to support operant responding as primary reinforcers (i.e. not conditioned reinforcers)17-22. Auditory and visual stimuli are self-administered by several species18,21,23, although surprisingly little is known about the neural mechanisms underlying this reinforcement. The operant sensation seeking (OSS) model is a robust model for obtaining sensory self-administration in the mouse, allowing the study of neural mechanisms important in sensory reinforcement24. An additional advantage of OSS is the ability to screen mutant mice for differences in operant behavior that may be relevant to addiction. We have reported that dopamine D1 receptor knockout mice, previously shown to be deficient in psychostimulant self-administration, also fail to acquire OSS24. This is a unique finding in that these mice are capable of learning an operant task when food is used as a reinforcer. While operant studies using food reinforcement can be useful in the study of general motivated behavior and the mechanisms underlying food reinforcement, as mentioned above, these studies are limited in their application to studying molecular mechanisms of drug addiction. Thus, there may be similar neural substrates mediating sensory and psychostimulant reinforcement that are distinct from food reinforcement, which would make OSS a particularly attractive model for the study of drug addiction processes. The degree of overlap between other molecular targets of OSS and drug reinforcers is unclear, but is a topic that we are currently pursuing. While some aspects of addiction such as resistance to extinction may be observed with OSS, we have found that escalation 25 is not observed in this model24. Interestingly, escalation of intake and some other aspects of addiction are observed with self-administration of sucrose26. Thus, when non-drug operant procedures are desired to study addiction-related processes, food or sensory reinforcers can be chosen to best fit the particular question being asked. 
In conclusion, both food self-administration and OSS in the mouse have the advantage of not requiring an intravenous catheter, which allows a higher throughput means to study the effects of pharmacological or genetic manipulation of neural targets involved in motivation. While operant testing using food as a reinforcer is particularly useful in the study of the regulation of food intake, OSS is particularly apt for studying reinforcement mechanisms of sensory stimuli and may have broad applicability to novelty seeking and addiction.

In this protocol we describe a method of operant learning using sensory stimuli as a reinforcer in the mouse. It requires no prior training or food restriction, and it allows the study of motivated behavior without the use of a pharmacological or natural reinforcer such as food.

Operant methods are powerful behavioral tools for the study of motivated behavior.  These 'self-administration' methods have been used extensively in drug ...

Neuroscience

Segmentation and Measurement of Fat Volumes in Murine Obesity Models Using X-ray Computed Tomography

Obesity is associated with increased morbidity and mortality as well as reduced metrics in quality of life.1 Both environmental and genetic factors are associated with obesity, though the precise underlying mechanisms that contribute to the disease are currently being delineated.2,3 Several small animal models of obesity have been developed and are employed in a variety of studies.4 A critical component to these experiments involves the collection of regional and/or total animal fat content data under varied conditions.
Traditional experimental methods available for measuring fat content in small animal models of obesity include invasive (e.g. ex vivo measurement of fat deposits) and non-invasive (e.g. Dual Energy X-ray Absorptiometry (DEXA), or Magnetic Resonance (MR)) protocols, each of which presents relative trade-offs. Current invasive methods for measuring fat content may provide details for organ and region specific fat distribution, but sacrificing the subjects will preclude longitudinal assessments. Conversely, current non-invasive strategies provide limited details for organ and region specific fat distribution, but enable valuable longitudinal assessment. With the advent of dedicated small animal X-ray computed tomography (CT) systems and customized analytical procedures, both organ and region specific analysis of fat distribution and longitudinal profiling may be possible. Recent reports have validated the use of CT for in vivo longitudinal imaging of adiposity in living mice.5,6 Here we provide a modified method that allows for fat/total volume measurement, analysis and visualization utilizing the Carestream Molecular Imaging Albira CT system in conjunction with PMOD and Volview software packages.

Fat content analysis is routinely conducted in studies utilizing murine obesity models. Emerging methods in small animal CT imaging and analysis are providing for longitudinal detail rich fat content analysis. Here we detail step by step procedures for performing small animal CT imaging, analysis, and visualization.

Obesity is associated with increased morbidity and mortality as well as reduced metrics in quality of life.1 Both environmental and genetic factors are ...

Methods for Intravenous Self Administration in a Mouse Model

Animal models have been developed to study the reinforcing effects of drugs, including the intravenous self-administration (IVSA) paradigm. The advantages of using an IVSA paradigm to study the reinforcing properties of drugs of abuse such as cocaine include the fact that the drug is self-administered instead of experimenter-administered, the schedule of reinforcement can be altered, and accurate measurement of the quantities of drug consumed as well as the timing and pattern of IV injections can be obtained. Furthermore, the intravenous route of administration avoids potential confounds related to first pass metabolism or taste, and produces rapid increases in blood and brain drug levels. As outlined in this video, intravenous self-administration can be obtained without prior food restriction or prior drug training following careful catheter placement during surgery and meticulous daily catheter flushing and maintenance. Experimental procedures outlined in this paper include a description of animal housing and acclimation methods, operant training using sweetened milk solutions, and catheter implantation surgery.

The intravenous self-administration (IVSA) paradigm is considered to be the gold standard in examining the reinforcing properties of drugs of abuse in rodents. This manuscript outlines the experimental procedures and surgical techniques necessary to obtain reliable IVSA data. In particular, meticulous catheter implantation and maintenance are highlighted.

Animal models have been developed to study the reinforcing effects of drugs, including the intravenous self-administration (IVSA) paradigm. The advantages ...

Progressive-ratio Responding for Palatable High-fat and High-sugar Food in Mice

Foods that are rich in fat and sugar significantly contribute to over-eating and escalating rates of obesity. The consumption of palatable foods can produce a rewarding effect that strengthens action-outcome associations and reinforces future behavior directed at obtaining these foods. Increasing evidence that the rewarding effects of energy-dense foods play a profound role in overeating and the development of obesity has heightened interest in studying the genes, molecules and neural circuitry that modulate food reward1,2. The rewarding impact of different stimuli can be studied by measuring the willingness to work to obtain them, such as in operant conditioning tasks3. Operant models of food reward measure acquired and voluntary behavioral responses that are directed at obtaining food. A commonly used measure of reward strength is an operant procedure known as the progressive ratio (PR) schedule of reinforcement.4,5 In the PR task, the subject is required to make an increasing number of operant responses for each successive reward. The pioneering study of Hodos (1961) demonstrated that the number of responses made to obtain the last reward, termed the breakpoint, serves as an index of reward strength4. While operant procedures that measure changes in response rate alone cannot separate changes in reward strength from alterations in performance capacity, the breakpoint derived from the PR schedule is a well-validated measure of the rewarding effects of food. The PR task has been used extensively to assess the rewarding impact of drugs of abuse and food in rats (e.g.,6-8), but to a lesser extent in mice9. The increased use of genetically engineered mice and diet-induced obese mouse models has heightened demands for behavioral measures of food reward in mice. In the present article we detail the materials and procedures used to train mice to respond (lever-press) for a high-fat and high-sugar food pellets on a PR schedule of reinforcement. We show that breakpoint response thresholds increase following acute food deprivation and decrease with peripheral administration of the anorectic hormone leptin and thereby validate the use of this food-operant paradigm in mice.

The present report details the protocol employed to measure the rewarding effects of high-fat food in mice using a progressive ratio operant conditioning task.

Foods that are rich in fat and sugar significantly contribute to over-eating and escalating rates of obesity. The consumption of palatable foods can ...

Reducing Research Animal Stress with Micropipette-Guided Drug Administration

Use of Micropipette-Guided Drug Administration as an Alternative Method to Oral Gavage in Rodent Models

Oral gavage (OG) with the use of a cannula attached to a syringe is one of the most common methods used to deliver precise dosing of compounds to the stomach of research animals. Unfortunately, this method comes with difficulties for both the operator and the research animal. Studies have shown that OG may lead to complications, including esophagitis, perforation of the esophagus, and inadvertent tracheal drug administration. In addition, OG is associated with increased plasma and fecal corticosterone levels (due to stress), altered blood pressure, and increased heart rate, which could negatively influence or bias study results. A previously developed alternative method termed micropipette-guided drug administration (MDA) incentivizes the animal to consume treatments readily in a minimally invasive manner. Herein, we present examples of the use of the MDA technique with treatments reconstituted in different vehicles and demonstrate effective delivery of the varied treatments to multiple different mouse strains. We further demonstrate that MDA is a technique that decreases the timing and invasiveness of drug administration and does not affect the gut microbiome composition as assessed by quantitative analysis of core gut microbial species. Overall, MDA may offer a less stressful and effective alternative to OG.

Here, we describe micropipette-guided drug administration (MDA) as an alternative method to oral gavage that incentivizes the research animal to ingest treatments readily with minimal stress and discomfort.

Oral gavage (OG) with the use of a cannula attached to a syringe is one of the most common methods used to deliver precise dosing of compounds to the ...

Cancer Research

Investigating Binge Eating Disorder with a Palatable Food Access Mouse Model

Intermittent Binge-Intake Model in Mice

Obesity affects one in eight individuals globally. Overeating, especially high-calorie foods, plays a significant role in obesity. Binge eating disorder (BED) is a complex condition caused by a combination of biological, psychological, and social factors. It involves excessive consumption of high-calorie foods in a short period and is often linked to anxiety and cravings.
Here, we present a protocol employing continuous and intermittent access to a new highly palatable food (HPF) -- M&amp;M&#39;s -- to develop a mouse model for investigating binge eating disorder (BED). The HPF, chosen for its high fat and sugar content, represents an optimal food source to study due to its strong palatability, which makes it particularly suited for examining compulsive eating behaviors. Using C57BL/6 mice, we provided continuous or intermittent access to M&amp;M&#39;s while allowing unrestricted access to standard chow and water. By the 8th day, the mice in the intermittent access group exhibited pronounced binge-eating behaviors, which persisted through the 26th day. These mice also consumed significantly more calories -- predominantly from the confectionary -- than those in the continuous access and control groups. The contrast between continuous and intermittent access underscores the critical role of feeding schedules in promoting the overconsumption of palatable foods.
Furthermore, behavioral assessments revealed intermittent access to the HPF-induced anxiety-like behaviors, highlighting the psychological impact of access patterns on both eating behavior and emotional states. By incorporating these two distinct feeding paradigms, this study offers valuable insights into how the availability of highly palatable foods can exacerbate binge-eating tendencies. This model provides a more realistic approach to studying binge-eating behaviors and their metabolic consequences. It highlights the importance of standardized models in biomedical research. Our findings offer insights into the physiological and neural mechanisms underlying BED, which could pave the way for developing effective therapeutic interventions for BED and obesity.

Author Spotlight: Accessible M&amp;M-Based Mouse Model for Investigating Binge Eating Disorder - Insights into Eating Behaviors, Anxiety, and Neural Mechanisms

A binge-eating model was established in mice using intermittent access to M&amp;M's (a highly palatable food made of fat and sugar). Mice with intermittent access to this high-fat, high-sugar food showed stress-like behaviors, increased caloric intake, and a preference for that food over standard chow compared to mice with continuous or no access to the food.

Obesity affects one in eight individuals globally. Overeating, especially high-calorie foods, plays a significant role in obesity. Binge eating disorder ...

An Advanced Murine Model for Nonalcoholic Steatohepatitis in Association with Type 2 Diabetes

Obesity is associated with chronic low-grade inflammation and insulin resistance, contributing to an increasing prevalence of chronic metabolic diseases, such as type 2 diabetes and nonalcoholic steatohepatitis (NASH). Recent research has established that pro-inflammatory immune cells infiltrate obese hypertrophic adipose tissue and liver. Given the emerging importance of immune cells in the context of metabolic homeostasis, there is a critical need to quantify and characterize their modification during the development of type 2 diabetes and NASH. However, animal models that induce pathophysiological features typical of human NASH are sparse.
In this article, we provide a detailed protocol to identify immune cell subsets isolated from liver and adipose tissue in a reliable mouse model of NASH, established by housing high-fat diet (HFD) mice under non-specific pathogen-free (SPF) conditions without a barrier for at least seven weeks. We demonstrate the handling of mice in non-SPF conditions, digestion of the tissues and identification of macrophages, natural killer (NK) cells, dendritic cells, B and T cell subsets by flow cytometry. Representative flow cytometry plots from SPF HFD mice and non-SPF mice are provided. To obtain reliable and interpretable data, the use of antibodies, accurate and precise methods for tissue digestion and proper gating in flow cytometry experiments are critical elements.
The intervention to restore physiological antigen exposure in mice by housing them in non-SPF conditions and unspecific exposure to microbial antigens could provide a relevant tool for investigating the link between immunological alterations, diet-induced obesity and related long term complications.

A simple and reliable diet-induced rodent animal model for nonalcoholic steatohepatitis (NASH) is described, achieved through non-SPF housing of the animals and administration of a specific high-fat diet. We describe identification of hepatic and adipose immune cell subsets to recapitulate human immunological conditions by exposing mice to environmental germs.

Obesity is associated with chronic low-grade inflammation and insulin resistance, contributing to an increasing prevalence of chronic metabolic diseases, ...

Immunology and Infection

Body Composition and Metabolic Caging Analysis in High Fat Fed Mice

Alterations to body composition (fat or lean mass), metabolic parameters such as whole-body oxygen consumption, energy expenditure, and substrate utilization, and behaviors such as food intake and physical activity can provide important information regarding the underlying mechanisms of disease. Given the importance of body composition and metabolism to the development of obesity and its subsequent sequelae, it is necessary to make accurate measures of these parameters in the pre-clinical research setting. Advances in technology over the past few decades have made it possible to derive these measures in rodent models in a non-invasive and longitudinal fashion. Consequently, these metabolic measures have proven useful when assessing the response of genetic manipulations (for example knockout or transgenic mice, viral knock-down or overexpression of genes), experimental drug/compound screening and dietary, behavioral or physical activity interventions. Herein, we describe the protocols used to measure body composition and metabolic parameters using an animal monitoring system in chow-fed and high fat diet-fed mice.

This protocol describes the use of a body composition analyzer and metabolic animal monitoring system to characterize body composition and metabolic parameters in mice. An obesity model induced by high-fat feeding is used as an example for the application of these techniques.