Food avoidance learning based on voluntary wheel running in laboratory mice (Mus musculus)

Running-based food aversion learning in freely-fed and hydrated rats: Daily monitoring of running-induced nausea by measuring kaolin clay ingestion

The main objective of this research was to demonstrate food aversion learning in rats with unrestricted access to food and water, using wheel running as the unconditioned stimulus. Experiment 1 showed that the target-running paired training group consumed a statistically smaller amount of the target food (tteok rice cakes) compared to the target/running unpaired control group, but the decrease in consumption over days in the paired group was not fully supported by a statistical test. Experiment 2a improved the methodology by familiarizing rats with tteok before training, which resulted in both a statistically significant group effect and a statistically significant daily decrease in tteok consumption. Experiment 2b demonstrated that tteok aversion could be reacquired after an extinction phase. These experiments indicate that running-based tteok aversion in non-deprived rats is a valid example of Pavlovian conditioning and suggest that wheel running can cause similar effects in unrestricted rats as observed in food- or water-restricted rats. Additionally, daily measurements of kaolin clay ingestion suggested that wheel running induced nausea in the rats of these experiments.

Food avoidance learning based on swimming in laboratory mice (Mus musculus)

Although it is now well documented that laboratory rats learn to avoid the flavored substance consumed immediately before running in activity wheels or swimming in water buckets, research on this activity-based flavor avoidance learning in other species is limited. Recently, running-based flavor avoidance learning has been demonstrated in laboratory mice by employing a method of resistance-to-habituation of neophobic reaction to novel food; mice that repeatedly experience running after encountering a novel food have a prolonged tendency to reject that food compared to control mice without paired running. The present article reports a series of attempts to obtain evidence of flavor avoidance learning based on swimming rather than running using this resistance-to-habituation method. Swimming-based flavor avoidance was clearly demonstrated in a differential conditioning paradigm; however, its demonstration in a simple conditioning paradigm requires a post-training choice test of the target food and another type of food. These results are likely due to the short swimming time (20min) and the formation of weak flavor aversion.

Food avoidance learning based on entirely voluntary wheel running in laboratory mice (Mus musculus)

Previous studies (Nakajima, 2019a,b) demonstrated food avoidance learning based on wheel running in laboratory mice: Consumption of a target snack becomes suppressed if it is repeatedly paired with an opportunity to run in an activity wheel. This is a kind of Pavlovian conditioning, because the avoidance is specific to the paired snack. For example, in an experiment, mice were initially trained to run in closed wheels. Then, access to one of the two kinds of snacks (cheese or raisins, counterbalanced) was followed by confinement in a large pet cage with an open wheel, while access to the other snack was not. After several repetitions of these two types of trials, differentiation in consumption between the two snacks emerged: The intake of the unpaired snack increased gradually over days, while the increase was attenuated for the running-paired snack. The present study replicated this food avoidance learning without the pretraining of running in a closed wheel, emphasizing the intrinsic capacity of running to establish food avoidance. The results somewhat suggest that pretraining in open wheels facilitates running-based food avoidance, but this effect was too weak in the present study to draw a clear conclusion.

Further demonstration of running-based food avoidance learning in laboratory mice (Mus musculus)

Voluntary wheel running has hedonically bivalent properties in laboratory rats and mice. While it works as a reward for instrumental performance such as bar pressing, it also functions as an aversive stimulus to establish Pavlovian conditioned avoidance of the paired stimulus. The present study focused on the latter case. Running in closed wheels hampered habituation of a reluctance to eat a target snack in rats (Experiment 1A) and mice (Experiment 1B) trained by pairing access to a target snack with confinement to a wheel attached to the cage. Experiment 2 successfully confirmed and extended this finding with mice running in both open and closed wheels. A differential conditioning procedure employed in Experiment 3 ensured that this phenomenon is specific to the snack paired with running, implying that it reflects Pavlovian conditioned flavor avoidance (CFA). Free exploration in cages without wheels, however, did not results in a CFA.