The overall goal of this procedure is to assess the power of the social transmission of food preferences for the study of socially induced olfactory memory, and the detection of Alzheimer's disease. These methods can help answer key questions in the behavioral neuroscience field, such as how do rodents communicate to others or transmit olfactory cues. This technique has the potential for the diagnosis of Alzheimer's disease as olfactory cognition dysfunction during early stages of the disease, may be useful for the detection of Alzheimer's.
Before beginning the social transmission of food preferences, or STFP procedure, bury a chocolate chip cookie in a random corner of a clean individual housing cage approximately one centimeter beneath the bedding surface and place the observer mouse into the cage. Record the latency to find the cookie with a 15 minute cutoff to rule out olfaction detection deficits and to prevent time consuming, unnecessary STFP testing. Next, lower the walls to separate the right and left compartments and place one container filled with regular food chow pellets in each of two corners of the three chamber apparatus.
Gently place the observer mouse in the center chamber and let the subject mouse habituate to the apparatus for 10 minutes. Then, open the sliding doors and let the subject mouse freely explore the whole apparatus for another 10 minutes. The next day, lower the walls to separate the right and left compartments again, and place a demonstrator mouse inside a wire containment cup.
Place the cup in the center chamber and write the abbreviation of the food with which the demonstrator has been cued on the lid of the wire cup facing the mounted camera. Gently place the subject mouse in the center chamber and let the subject mouse freely explore the demonstrator mouse for 30 minutes. At the end of the exploration period, weigh each mouse and label each animal with an observed ID and flavor.
Then, remove the wall divides and place one food container of the cued food into one corner of the three chamber apparatus and one food container of a novel, uncued food into another corner of the apparatus. Gently place the subject mouse in the middle chamber and let the mouse freely explore the whole arena for 120 minutes. Then, measure the food preference by weighing the remaining food.
In the representative social exploration phase analysis, wild type mice did not demonstrate any differences in the total distance moved or time spent with the demonstrator mouse compared to the transgenic, Alzheimer's disease mice. During the food preference test phase, the wild type animal remembered its previous contact with the odor and preferred to eat more, and to spend more time with the matching flavored food, indicating an intact, socially induced food memory. The mutant animals, however, did not show a preference for the cued food over the novel, uncued food, indicative of a decreased, socially induced food memory.
Once mastered, this technique can be completed in three hours per subject mouse over three consecutive days, if performed properly. Before and after attempting this procedure, it's important to remember to thoroughly clean the equipment and the inside of the arena to prevent olfactory cue biases between mice. This technique is based on the phenomenon of a naive observer rodent exhibiting an enhanced preference for a specific food after interaction with the demonstrate rodents that ate the same food.
Though this methods can provide insights into olfactory learning and memory in Alzheimer's disease transgenic mouse models, it can also be used in other mouse models of neuropsychiatric disorders characterized by olfactory recondition and memory deficits. After watching this video, you should have a good understanding of how to assess social enhancements of diet preference in mice.
