The authors wish to acknowledge funding from UL1TR000071 (NCATS), P30DK079638 (NIDDK), P30DA028821 (NIDA) and T32DA07287 (NIDA).

All experimental procedures are in accordance with the Guide for the Care and Use of Laboratory Animals (Institute of Laboratory Animal Resources (U.S.), 1996) and with the approval of the Institutional Animal Care and Use Committee at the University of Texas Medical Branch.
1. Subjects
<ol>
	<li>Single house male Sprague-Dawley rats weighing 225-250 g at 21 &#176;C and 30-50% relative humidity with a 12 hr light-dark cycle (lights on 6:00 am-6:00 pm).</li>
	<li>Maintain rats on a low fat food (10% fat by energy). Habituate rats to food and colony room for at least 7 days prior to experimentation. Animals are habituated to handling and dosing of vehicle for three days prior to starting the studies. The first day after habituation is experimental Day 1.</li>
</ol>
2. Baseline Preference
<ol>
	<li>Day 1, fill two clean food hoppers, one marked with an A and the other with B, with 10% fat food for each cage. Weigh the food hoppers (with food) and place them in the cage, ensuring the rat has access to both.</li>
	<li>Day 2, at approximately the same time food hoppers were placed in the cage the day before, record the food hopper weights and switch the positions of hopper A and hopper B. This mitigates position bias. Always examine the home cage for any food removed from the hopper, weigh it, and account for it. Food intake is measured by change in hopper weight between days.</li>
	<li>Day 3, record the food hopper weights as before. Examine the amount of food consumed in each food hopper position and food hopper identification (A and B). This data gives a baseline understanding of position bias and specific hopper preference, and should have a preference score of approximately 50% indicating no preference. Throw out the remaining food.</li>
</ol>
3. Fat Preference
<ol>
	<li>Day 3, obtain two clean food hoppers for each cage. It is important to use clean food hoppers whenever switching between the different foods to prevent confounding scents from previous experiments. Fill hopper A with 12.5% fat food and hopper B with 15% fat food (Table 1). Record the starting weights of each hopper and place both in the cage.</li>
	<li>Day 4, record the weights of each hopper, switching the positions of hopper A and hopper B upon placing them back in the cage.</li>
	<li>Day 5, record the weights of each hopper. After determining the grams of each food consumed on both days, the rat&#8217;s food preference can be determined.</li>
	<li>Repeat steps 3.1 through 3.3 multiple times with the same animals using 12.5% fat food as compared to foods with increasing fat content (e.g. first 15%, next 17.5%, then 20%, and lastly 45% fat).</li>
</ol>
4. Data Calculations and Analysis
<ol>
	<li>Calculate the daily food intake for each animal by subtracting the final mass of the food+hopper from the starting mass of the food+hopper. Because each food is measured over 2&#160;days, the 2&#160;day total can be added together for each % fat content.</li>
	<li>Calculate the fat preference score by dividing the intake of the higher fat food from the total food consumed over each two day period. For example, one rat ate 8.9 g&#160;of the 12.5% fat diet and 27.5 g &#160;of the 17.5% diet over 2&#160;days. Therefore the preference score for that individual animal is 76% (27.5 divided by 36.4).</li>
	<li>Average and graph the preference score for each diet (15%, 17.5%, 20%, and 45% fat) (Figure 3). The total food intake is also informative and can readily be plotted as grams (Figure 4).</li>
	<li>Express the preference score (Figure 5A) and total food intake (Figure 5B) as a function of total energy intake (kilocalories) using the energy density in Table 1.</li>
	<li>If using more than one group of animals, perform a two-way repeated measures ANOVA followed by a Bonferroni post-test. Power analysis indicates that n = 8 animals per group is appropriate for detecting a difference of 7% between treatment groups.</li>
</ol>

<ol>
	<li>Flegal, K. M., Carroll, M. D., Ogden, C. L., Curtin, L. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prevalence+and+trends+in+obesity+among+US+adults.">Prevalence and trends in obesity among US adults.</a> JAMA. 303 (3), 235-241 (1999).</li><li>Mokdad, A. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prevalence+of+obesity,+diabetes,+and+obesity-related+health+risk+factors.">Prevalence of obesity, diabetes, and obesity-related health risk factors.</a> JAMA. 289 (1), 76-79 (2003).</li><li>Abete, I., Astrup, A., Mart&#237;nez, J. A., Thorsdottir, I., Zulet, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Obesity+and+the+metabolic+syndrome:+role+of+different+dietary+macronutrient+distribution+patterns+and+specific+nutritional+components+on+weight+loss+and+maintenance.">Obesity and the metabolic syndrome: role of different dietary macronutrient distribution patterns and specific nutritional components on weight loss and maintenance.</a> Nutr. Rev. 68 (4), 214-231 (2010).</li><li>Berthoud, H. R., M&#252;nzberg, H., Richards, B. K., Morrison, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+and+metabolic+regulation+of+macronutrient+intake+and+selection.">Neural and metabolic regulation of macronutrient intake and selection.</a> Proc. Nutr. Soc. 71 (3), 390-400 (2012).</li><li>Warwick, Z. S., Schiffman, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+dietary+fat+in+calorie+intake+and+weight+gain.">Role of dietary fat in calorie intake and weight gain.</a> Neurosci. Biobehav. Rev. 16 (4), 585-596 (1992).</li><li>Kendall, A., Levitsky, D. A., Strupp, B. J., Lissner, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Weight+loss+on+a+low-fat+diet:+consequence+of+the+imprecision+of+the+control+of+food+intake+in+humans.">Weight loss on a low-fat diet: consequence of the imprecision of the control of food intake in humans.</a> Am. J. Clin. Nutr. 53 (5), 1124-1129 (1991).</li><li>Ackroff, K., Sclafani, A., Montmayeur, J. P., leCoutre, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oral+and+Postoral+Determinants+of+Dietary+Fat+Appetite.">Oral and Postoral Determinants of Dietary Fat Appetite.</a> Fat Detection: Taste, Texture, and Post Ingestive Effects. Chapter 12. , (2010).</li><li>West, D. B., York, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dietary+fat,+genetic+predisposition,+and+obesity:+lessons+from+animal+models.">Dietary fat, genetic predisposition, and obesity: lessons from animal models.</a> Am. J. Clin. Nutr. 67, 505-512 (1998).</li><li>Sclafani, A., Ackroff, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+gut+nutrient+sensing+in+stimulating+appetite+and+conditioning+food+preferences.">Role of gut nutrient sensing in stimulating appetite and conditioning food preferences.</a> Am. J. Physiol. Regul. Integr. Comp. Physiol. 302 (10), (2012).</li><li>Velloso, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+brain+is+the+conductor:+diet-induced+inflammation+overlapping+physiological+control+of+body+mass+and+metabolism.">The brain is the conductor: diet-induced inflammation overlapping physiological control of body mass and metabolism.</a> Arq. Bras. Endocrinol. Metabol. 53 (2), 151-158 (2009).</li><li>Vanzela, E. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pregnancy+restores+insulin+secretion+from+pancreatic+islets+in+cafeteria+diet-induced+obese+rats.">Pregnancy restores insulin secretion from pancreatic islets in cafeteria diet-induced obese rats.</a> Am. J. Physiol. Regul. Integr. Comp. Physiol. 298 (2), (2010).</li><li>Johnson, S. L., McPhee, L., Birch, L. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conditioned+preferences:+young+children+prefer+flavors+associated+with+high+dietary+fat.">Conditioned preferences: young children prefer flavors associated with high dietary fat.</a> Physiol. Behav. 50 (6), 1245-1251 (1991).</li><li>Bolanos, C. A., Barrot, M., Berton, O., Wallace-Black, D., Nestler, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methylphenidate+treatment+during+pre-+and+periadolescence+alters+behavioral+responses+to+emotional+stimuli+at+adulthood.">Methylphenidate treatment during pre- and periadolescence alters behavioral responses to emotional stimuli at adulthood.</a> Biol. Psychiatry. 54, 1317-1329 (2003).</li><li>Ignar, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+Ingestive+Behaviors+in+the+Rat+by+GSK1521498,+a+Novel+{micro}-Opioid+Receptor-Selective+Inverse+Agonist.">Regulation of Ingestive Behaviors in the Rat by GSK1521498, a Novel {micro}-Opioid Receptor-Selective Inverse Agonist.</a> J. Pharmacol. Exp. Ther. 339, 24-34 (2011).</li><li>Benzon, C. R., Johnson, S. B., McCue, D. L., Li, D., Green, T. A., Hommel, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuromedin+U+receptor+2+knockdown+in+the+paraventricular+nucleus+modifies+behavioral+responses+to+obesogenic+high-fat+food+and+leads+to+increased+body+weight.">Neuromedin U receptor 2 knockdown in the paraventricular nucleus modifies behavioral responses to obesogenic high-fat food and leads to increased body weight.</a> Neuroscience. , (2013).</li><li>Lucas, F., Ackroff, K., Sclafani, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dietary+fat-induced+hyperphagia+in+rats+as+a+function+of+fat+type+and+physical+form.">Dietary fat-induced hyperphagia in rats as a function of fat type and physical form.</a> Physiol Behav. 45 (5), 937-946 (1989).</li></ol>

The authors have nothing to disclose.

The Fat Preference model is an informative and easy to perform assay of feeding behavior. This assay offers an opportunity to identify neural and molecular mechanisms which underlie food preference, which is an important yet understudied area of obesity research. Changes in fat preference from genetic differences or pharmacological manipulations could be visualized as rightward or leftward shifts in the preference curve (Figure 3B). It is important to include the middle fat foods (15%, 17.5%, and 20%) to...

Obesity is a prevalent problem in the United States1, with the Centers for Disease Control and Prevention estimating that over a third of American adults are obese. Obesity has also been identified as a risk factor for numerous health concerns, including type 2 diabetes, high blood pressure, and high cholesterol2. While many factors have been shown to influence the increase in obesity rates, there is ongoing interest and controversy in the role macronutrients play in obesity3,4.
One contributing factor to obesity is high dietary fat intake5. Increased dietary fat is correlated with increased human energy consumption6 and significant increases in body fat content7,8. Additionally, dietary fat has reward value both during and after consumption7,9. Therefore, determining what factors influence preference for high fat foods can both guide pharmacotherapeutic design and promote understanding of the underlying dietary choices that can lead to obesity. The Fat Preference model described here tests for rats&#8217; preference between foods of differing fat content, but similar nutritional value. Specifically, this model presents the rats with a choice of two different foods simultaneously thus enabling the quantification of preference based on grams consumed of the lower fat food verses the higher fat food. Pharmacological and genetic effects can be measured as a change in preference for the food with higher fat content.
The Fat Preference model serves to complement the widely used palatable food intake models10 but also offers several advantages. This model allows the experimenter to specifically assess feeding behavior in a controlled environment in which two food options are available. Traditional high fat feeding models only offer one food which eliminates the capacity to study food choice, an important aspect of human food intake. Some assays do offer multiple food types and are often referred to as &#34;cafeteria&#34; type feeding studies11. These studies suffer from reproducibility because human food is often used in the assay and is not well suited to the laboratory environment due to nutrient variability. We use defined diets which contain individual purified ingredients thus greatly improving reproducibility and flexibility to change macronutrient content such as dietary fat. With higher dietary fat intake associated with obesity in humans5 and the natural human preference for higher fat foods12, treatments that alter rat preference for high fat foods can provide valuable insight into obesity.

<table border="0" cellpadding="0" cellspacing="0" width="673">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:277px;">&#160;Rodent diet with 10 kcal% fat&#160;</td>
			<td style="width:111px;">Research Diets</td>
			<td style="width:119px;">D12450B</td>
			<td style="width:167px;">10 % fat rat food</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:277px;">&#160;Rodent diet with 12.5 kcal% fat&#160;</td>
			<td style="width:111px;">Research Diets</td>
			<td style="width:119px;">D07040501</td>
			<td>12.5 % fat rat food</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:277px;">&#160;Rodent diet with 15 kcal% fat&#160;</td>
			<td style="width:111px;">Research Diets</td>
			<td style="width:119px;">D07040502</td>
			<td>15 % fat rat food</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:277px;">&#160;Rodent diet with 17.5 kcal% fat&#160;</td>
			<td style="width:111px;">Research Diets</td>
			<td style="width:119px;">D07040503</td>
			<td>17.5 % fat rat food</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:277px;">&#160;Rodent diet with 20 kcal% fat&#160;</td>
			<td style="width:111px;">Research Diets</td>
			<td style="width:119px;">D07040504</td>
			<td>20 % fat rat food</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:277px;">&#160;Rodent diet with 45 kcal% fat&#160;</td>
			<td style="width:111px;">Research Diets</td>
			<td style="width:119px;">D12451</td>
			<td>45 % fat rat food</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:277px;">Rat feeders (3.75&#34;W x 2.875&#34;D x 5.25&#34;H)</td>
			<td style="width:111px;">Labex of MA</td>
			<td style="width:119px;">2528</td>
			<td>Food hoppers</td>
		</tr>
	</tbody>
</table>

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.

Rats had physical access to both food hoppers simultaneously (Figure 1) in order to demonstrate preference for available food choices with differing fat content (Table 1). Rat food was weighed daily and any food spillage was easily found and accounted for (Figure 2). Spillage of fine food particles was found to be minimal and does not substantially influence the data. Using the Fat Preference model, a clear preference between foods containing 12.5% fat and higher fat foo...

Watch this Scientific Journal Video about Fat Preference: A Novel Model of Eating Behavior in Rats at JoVE.com

Fat Preference: A Novel Model of Eating Behavior in Rats

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 ...

fat-preference-a-novel-model-of-eating-behavior-in-rats

Research

JoVE Journal

Behavior

13.1K Views.  University of Texas Medical Branch.  Влияет содержание пищевых жиров и потребление энергии и жира состава тела у млекопитающих. Изучив предпочтения крыс для высокой жирной пищи в серии экспериментов выбор, можно проверить генетические различия и фармакологические меры по их предпочтение высо?...

Video: Fat Preference: A Novel Model of Eating Behavior in Rats

High Fat Diet Feeding and High Throughput Triacylglyceride Assay in Drosophila Melanogaster

Heart disease is the number one cause of human death worldwide. Numerous studies have shown strong connections between obesity and cardiac malfunction in humans, but more tools and research efforts are needed to better elucidate the mechanisms involved. For over a century, the genetically highly tractable model of Drosophila has been instrumental in the discovery of key genes and molecular pathways that proved to be highly conserved across species. Many biological processes and disease mechanisms are functionally conserved in the fly, such as development (e.g., body plan, heart), cancer, and neurodegenerative disease. Recently, the study of obesity and secondary pathologies, such as heart disease in model organisms, has played a highly critical role in the identification of key regulators involved in metabolic syndrome in humans.
Here, we propose to use this model organism as an efficient tool to induce obesity, i.e., excessive fat accumulation, and develop an efficient protocol to monitor fat content in the form of TAGs accumulation. In addition to the highly conserved, but less complex genome, the fly also has a short lifespan for rapid experimentation, combined with cost-effectiveness. This paper provides a detailed protocol for High Fat Diet (HFD) feeding in Drosophila to induce obesity and a high throughput triacylglyceride (TAG) assay for measuring the associated increase in fat content, with the aim to be highly reproducible and efficient for large-scale genetic or chemical screening. These protocols offer new opportunities to efficiently investigate regulatory mechanisms involved in obesity, as well as provide a standardized platform for drug discovery research for rapid testing of the effect of drug candidates on the development or prevention of obesity, diabetes and related metabolic diseases.

High Fat Diet Feeding and High Throughput Triacylglyceride Assay in Drosophila Melanogaster

This is a high fat diet feeding protocol to induce obesity in Drosophila, a model for understanding fundamental molecular mechanisms implicated in lipotoxicity. It also provides a high throughput triacylglyceride assay for measuring fat accumulation in Drosophila and potentially other (insect) models under various dietary, environmental, genetic or physiological conditions.

Heart disease is the number one cause of human death worldwide. Numerous studies have shown strong connections between obesity and cardiac malfunction in ...

Genetics

Hyponeophagia: A Measure of Anxiety in the Mouse

Before the present day, when fast-acting and potent rodenticides such as alpha-chloralose were not yet in use, the work of pest controllers was often hampered by a phenomenon known as "bait shyness". Mice and rats cannot vomit, due to the tightness of the cardiac sphincter of the stomach, so to overcome the problem of potential food toxicity they have evolved a strategy of first ingesting only very small amounts of novel substances. The amounts ingested then gradually increase until the animal has determined whether the substance is safe and nutritious. So the old rat-catchers would first put a palatable substance such as oatmeal, which was to be the vehicle for the toxin, in the infested area. Only when large amounts were being readily consumed would they then add the poison, in amounts calculated not to affect the taste of the vehicle. The poisoned bait, which the animals were now readily eating in large amounts, would then swiftly perform its function.
Bait shyness is now used in the behavioural laboratory as a way of measuring anxiety. A highly palatable but novel substance, such as sweet corn, nuts or sweetened condensed milk, is offered to the mice (or rats) in a novel situation, such as a new cage. The latency to consume a defined amount of the new food is then measured.
Robert M.J. Deacon can be reach at <a href="mailto:robert.deacon@psy.ox.ac.uk">robert.deacon@psy.ox.ac.uk</a>

Mice and rats, due to their innate cautiousness, are initially slow in consuming a novel food, particularly in a novel place. This hyponeophagia can readily be measured in the laboratory, even though laboratory animals are much less anxious than their wild counterparts

Before the present day, when fast-acting and potent rodenticides such as alpha-chloralose were not yet in use, the work of pest controllers was often ...

Neuroscience

Assessment of Social Transmission of Food Preferences Behaviors

Olfactory recognition deficits are suggested to be able to serve as clinical marker to differentiate Alzheimer&#39;s disease (AD) subjects from healthy aging groups. For example, olfactory dysfunction in AD can present as impairment in olfactory recognition, emerging during early stages of the disease and worsening while the disease progresses. The social transmission of food preferences (STFP) task is based on a rudimentary form of communication between rodents concerning distant foods dependent on the transmission of olfactory cues. Healthy wild-type mice would prefer to eat a novel, flavored food that was previously cued by a conspecific, and this food preference would be hampered in transgenic AD mice, such as the APP/PS1 model. Indeed, a strong preference for the cued food in C57Bl6/J mice of 3 months of age was found, and this was reduced in 3 months old transgenic APP/PS1 mice. In summary, STFP task could be a powerful measure to be integrated in present subclinical detection assays of AD.

This paper presents a protocol for the investigation of social transmission of food preference in mice. The advantages and possible applications for this procedure, for instance, in detecting early changes in AD mouse models, are highlighted. To conclude, interpretation of the results in light of critical details are discussed.

Olfactory recognition deficits are suggested to be able to serve as clinical marker to differentiate Alzheimer&#39;s disease (AD) subjects from healthy ...

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 ...

A Complex Diving-For-Food Task to Investigate Social Organization and Interactions in Rats

For many species, where status is a vital motivator that can affect health, social hierarchies influence behavior. Social hierarchies that include dominant-submissive relationships are common in both animal and human societies. These relationships can be affected by interactions with others and with their environment, making them difficult to analyze in a controlled study. Rather than a simple dominance hierarchy, this formation has a complicated presentation that allows rats to avoid aggression. Status can be stagnant or mutable, and results in complex societal stratifications. Here we describe a complex diving-for-food task to investigate rodent social hierarchy and behavioral interactions. This animal model may allow us to assess the relationship between a wide range of mental illnesses and social organization, as well as to study the effectiveness of therapy on social dysfunction.

This protocol describes a method of examining social hierarchy in a rat model. Rats perform a complex diving-for-food task in which they form a distinct hierarchy according to their willingness to dive underwater and swim to obtain a food pellet. This method is used to understand decision making and social relationships among highly social animals in small groups.

For many species, where status is a vital motivator that can affect health, social hierarchies influence behavior. Social hierarchies that include ...

Simultaneous Detection of c-Fos Activation from Mesolimbic and Mesocortical Dopamine Reward Sites Following Naive Sugar and Fat Ingestion in Rats

This study uses cellular c-fos activation to assess effects of novel ingestion of fat and sugar on brain dopamine (DA) pathways in rats. Intakes of sugars and fats are mediated by their innate attractions as well as learned preferences. Brain dopamine, especially meso-limbic and meso-cortical projections from the ventral tegmental area (VTA), has been implicated in both of these unlearned and learned responses. The concept of distributed brain networks, wherein several sites and transmitter/peptide systems interact, has been proposed to mediate palatable food intake, but there is limited evidence empirically demonstrating such actions. Thus, sugar intake elicits DA release and increases c-fos-like immunoreactivity (FLI) from individual VTA DA projection zones including the nucleus accumbens (NAC), amygdala (AMY) and medial prefrontal cortex (mPFC) as well as the dorsal striatum. Further, central administration of selective DA receptor antagonists into these sites differentially reduce acquisition and expression of conditioned flavor preferences elicited by sugars or fats. One approach by which to determine whether these sites interacted as a distributed brain network in response to sugar or fat intake would be to simultaneous evaluate whether the VTA and its major mesotelencephalic DA projection zones (prelimbic and infralimbic mPFC, core and shell of the NAc, basolateral and central-cortico-medial AMY) as well as the dorsal striatum would display coordinated and simultaneous FLI activation after oral, unconditioned intake of corn oil (3.5%), glucose (8%), fructose (8%) and saccharin (0.2%) solutions. This approach is a successful first step in identifying the feasibility of using cellular c-fos activation simultaneously across relevant brain sites to study reward-related learning in ingestion of palatable food in rodents.

The goal of this study is to identify reward-related distributed brain networks by delineating a reliable immunohistological technique using cellular c-fos activation to measure simultaneous changes in dopamine pathways and terminal sites after novel ingestion of fat and sugar in rats.

This study uses cellular c-fos activation to assess effects of novel ingestion of fat and sugar on brain dopamine (DA) pathways in rats. Intakes of sugars ...

A Rat Model of Central Fatigue Using a Modified Multiple Platform Method

In this article, we introduced a rat model of central fatigue using the modified multiple platform method (MMPM). The Multiple Platform box was designed as a water tank with narrow platforms on the bottom. The model rats were put into the tank and stood on the platforms for 14 h (18:00 - 8:00) per day for a consecutive 21 days, with a blank control group set for contrast. At the end of modeling, rats in the model group showed an obvious fatigued appearance. To assess the model, we performed several behavioral tests, including the open field test (OFT), the elevated plus maze (EPM) test, and the exhaustive swimming (ES) test. The results showed that anxiety, spatial cognition impairment, poor muscle performance, and declined voluntary activity presented in model rats confirm the diagnosis of&#160;central fatigue. Changes of the central neurotransmitters also verified the result. In conclusion, the model successfully simulated central fatigue, and future study with the model may help reveal the pathological mechanism of the disease.

Here, we present a protocol to introduce a rat model of central fatigue using the modified multiple platform method (MMPM).

In this article, we introduced a rat model of central fatigue using the modified multiple platform method (MMPM). The Multiple Platform box was designed ...

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.

Alterations to body composition (fat or lean mass), metabolic parameters such as whole-body oxygen consumption, energy expenditure, and substrate ...

Medicine

Palatable Western-style Cafeteria Diet as a Reliable Method for Modeling Diet-induced Obesity in Rodents

Obesity is rapidly increasing in incidence in developed and developing countries and is known to induce or exacerbate many diseases.&#160;The health burden of obesity and its comorbid conditions highlight the need for better understanding of its pathogenesis, yet ethical constraints limit studies in humans. To this end externally valid models of obesity in laboratory animals are essential for the understanding of being overweight and obesity.&#160;While many species have been used to model the range of changes that accompany obesity in humans, rodents are most commonly used. Our laboratory has developed a western-style cafeteria diet that consistently leads to considerable weight gain and markers of metabolic disease in rodents. The diet exposes rodents to a variety of highly palatable foods to induce hyperphagia, modeling the modern western food environment. This diet rapidly induces weight gain and body fat accumulation in rats allowing for the study of effects of overeating and obesity. While the cafeteria diet may not provide the same control over macronutrient and micronutrient profile as purified high-fat or high-fat, high-sugar diets, the cafeteria diet typically induces a more severe metabolic phenotype than that observed with purified diets and is more in line with metabolic disturbances observed in the overweight and obese human population.

This protocol describes the use of a highly palatable, western-style cafeteria diet to model overeating and obesity in rodents. Here, we provide a detailed outline of food selection, preparation and measurement, and explain methodological factors that assist in generating a robust and reproducible phenotype.

Obesity is rapidly increasing in incidence in developed and developing countries and is known to induce or exacerbate many diseases.&#160;The health ...

A Chronic High-Intensity Interval Training and Diet-Induced Obesity Model to Maximize Exercise Effort and Induce Physiologic Changes in Rats

Compared to continuous-moderate or low-intensity training, high-intensity interval training (HIIT) is a more time-efficient alternative method that results in similar physiologic benefits. This paper presents a HIIT protocol that can be used to assess various health markers in a Sprague-Dawley rat model of diet-induced obesity. Female Sprague Dawley rats aged 21 days old were randomly assigned to the following groups: control (CON, n = 10), exercise-trained (TRN, n = 10), high-fat diet (HFD, n = 10), and high-fat diet/exercise training (HFD/TRN, n = 10). The control diets consisted of commercial laboratory chow with 10% kilocalories (kcal) from fat (3.82 kcal/g), and the high-fat diets (HFD) consisted of 45% kcal from fat (4.7 kcal/g). The animals had ad libitum access to their assigned diet throughout the study. After an 8 week diet induction period, the exercise cohorts completed four HIIT sessions per week for 8 weeks. Each HIIT session consisted of 10 intervals of 1 min sprints/2 min rest using a rodent treadmill with a motor-driven belt. After the 8 weeks of training, the animals were sacrificed for tissue collection. The results revealed no differences in the distance run between the TRN and HFD/TRN groups, and the training speed steadily increased over the duration of the study, with a final running speed of 115 cm/s and 111 cm/s for the TRN and HFD/TRN groups, respectively. The weekly caloric intake was decreased (p &#60; 0.05) in the TRN group relative to the CON group but increased (p &#60; 0.05) in the HFD/TRN group relative to the HFD group. Lastly, the animals on the HFD had greater (p &#60; 0.05) adiposity, and the trained animals had reduced (p &#60; 0.05) adiposity relative to controls. This protocol demonstrates an efficient method to evaluate the effects of HIIT on various physiologic outcomes in a diet-induced obesity model.

This paper presents the morphometric responses and training performance outcomes of a high-intensity interval training (HIIT) protocol in a Sprague-Dawley rat model of diet-induced obesity. The purpose of this protocol was to maximize exercise intensity and determine the physiologic responses to HIIT in lean and obese rats.

Compared to continuous-moderate or low-intensity training, high-intensity interval training (HIIT) is a more time-efficient alternative method that ...