The overall goal of this procedure is to evaluate the effects of genetic and pharmacological manipulation on preference for dietary fat, which is a key factor underlying overconsumption of food and obesity. This is accomplished by first filling hoppers A and B with 10%fat food and measuring food consumption 24 hours later. The second step is to switch the positions of hoppers A and B and weigh them again the next day to determine the baseline feeding position bias.
Next, the fat preference can be determined by repeating the above steps multiple times with 12 point half and higher percent fat food. The final step is to calculate the preference score by dividing the grams of intake of the higher fat diet by the total food consumed of both diets. Ultimately, the fat preference model is used to show how experimental manipulations may change rat's preference for high fat food.
This method can help answer key questions in the obesity field, such as what pathways in the brain mediate high fat feeding behavior. This technique can be extended toward the development of therapies to treat obesity and eating disorders in particular, because we can selectively reduce intake of foods that are high in fat and sugar For the following protocol. Male spra dolly rats are singly housed and kept on a 12 hour light dark cycle.
Build the food hopper with a low fat food and habituate the rats to the food and colony room for at least seven days prior to experimentation for each of the three days before taking baseline measurements. Handle each test animal to reduce stress and dose them with vehicle to familiarize them with the dosing process if necessary. To begin the study on day one, fill two clean food hoppers with food containing 10%fat, and label them hoppers A and B.Weigh the filled food hoppers and place them in the cage ensuring the rat has access to both.
Allow the rat to eat freely from both hoppers for 24 hours the next day. At approximately the same time, record the weight of both food hoppers. Always examine the home cage for any food removed from the hopper.
If spilled food is found, weigh it along with the rest of the food. Return the hoppers to the cage, but switch the positions of hopper A and B to mitigate position bias. On the third day, record the food hopper weights as before.
Examine the amount of food consumed in each food hopper position to obtain a baseline understanding of position bias. After collecting baseline measurements, obtain two clean food hoppers and fill hopper A with food containing 12.5%fat, and hopper B with 15%fat food. After recording the starting weights of each hopper, place them both in the cage the next day.
Record the weights of each hopper as demonstrated earlier and switch their positions upon placing them back in the cage. On the fifth day. Record the weights of each hopper to determine the grams of food consumed and determine the rat's food preference.
The steps above can be repeated multiple times with the same animals using food with increasing levels of fat content. To calculate the daily food intake for each animal, subtract the final mass of the food plus hopper from the starting mass. Because each food is measured over two days, the two day total can be added together for each group.
Next, calculate the fat preference score by dividing the intake of the higher fat food from the total food consumed over each two day period. To express the preference score and total food intake as a function of total energy intake and energy density table is used by rats, demonstrate an increasing preference for foods with higher fat content preference for 15%17.5%20%and 45%fat foods is significantly greater when compared to 12.5%The fat preference method results in a dose effect curve where preference changes with fat content as compared to 12.5%fat food. Here, the preference for higher fat food is expressed as grams of food consumed, providing additional information about changes in total food intake over the course of the experiment.
When examined for levels of energy intake, the data show that rats consume more of their calories from higher fat foods during preference testing, depending on the fat percentage of the foods offered. This technique paves the way for researchers in the field of metabolic diseases to explore the complex behavioral phenomenon that underlies why we prefer certain types of foods that are high in fats and sugars such as french fries, hamburgers, and cookies. Once mastered, this technique can be performed in 40 minutes per day for 10 days.
