Swimming-based pica in rats

Pica behavior of laboratory rats (Rattus norvegicus domestica): Nauseated animals ingest kaolin, zeolite, bentonite, but not calcium carbonate chalk

"Pica" refers to the ingestion of non-nutritive substances by animals that would not typically consume them. The pica behavior can be utilized to investigate the internal conditions of animals' bodies. For example, rats, due to neuroanatomical reasons, cannot vomit; nevertheless, when nauseated, they ingest kaolin clay. This renders the ingestion of kaolin a practical proxy for measuring nausea in rats. The question of whether rats consume minerals other than kaolin during nauseous episodes remains unanswered. This study aims to identify a mineral better suited for detecting nausea in rats. In two experiments, nausea was induced in laboratory rats by a single dose of lithium chloride (0.15 M, 2% bw), and their mineral consumption over the 24-hour period was measured. Experiment 1 compared three minerals between rat groups: kaolin sold for nausea detection (kaolin A), kaolin for ceramics (kaolin B), and zeolite. Nauseated rats consumed all minerals, with the highest consumption occurring with kaolin B. In Experiment 2, three commercially available health soils were compared: edible kaolin, edible bentonite, and edible chalk. The most significant consumption was observed in the kaolin group, followed by the bentonite group, while nauseated rats did not consume edible chalk. These findings underscore the suitability of kaolin for nausea detection, although the extent of consumption may vary depending on the product.

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.

Pica caused by emetic drugs in laboratory rats with kaolin, gypsum, and lime as test substances

Pica refers to eating nonfood substances. The pica behavior has been the focus of attention in physiological and pharmacological studies, because its consumption is a good marker of nausea in laboratory rats, which cannot vomit due to neuroanatomical reasons. Almost all pica studies with rats have used kaolin clay pellets as nonfood substances. The present study primarily aimed to explore an alternative (or more suitable) substance to kaolin for detection of nausea induced by emetic drugs. Two calcium compounds, gypsum and lime, were evaluated in this study. An injection of lithium chloride (LiCl) increased pica behavior not only in the rats given kaolin but also in the rats given gypsum, suggesting that gypsum consumption could be used as an indicator of nausea. However, its sensitivity was no greater than that of kaolin consumption. In addition, lime is not a useful marker for nausea because the size of pica was small in the LiCl-injected rats, and did not differ from the control in the cisplatin-injected rats. In short, the superiority of kaolin as a test substance for nausea could not be overturned. However, the fact that nauseous rats displayed pica behavior with gypsum and lime refutes the claim that aluminosilicate, the main component of kaolin, is the critical determinant of emetic-caused pica in laboratory rats.

Food aversion learning based on voluntary running in non-deprived rats: a technique for establishing aversive conditioning with minimized discomfort

This article presents an experimental preparation for establishing conditioned food aversion (CFA) by voluntary wheel running in rats with laboratory chow and water freely available. In Experiment 1, unfamiliar food (raisins) was avoided by rats when they first encountered it. This neophobic food avoidance was habituated by repeated tests; the rats gradually increased their raisin consumption. However, the consumption remained suppressed in rats that accessed the raisins after wheel running. This finding implies that running yielded CFA, which suppressed consumption of the unfamiliar food rather than increasing it. Because running generated kaolin clay ingestion, which is a behavioral marker of nausea, it is suggested that the running-based CFA was mediated by weak gastrointestinal discomfort. Experiment 2 supported the claim that the suppressed consumption is due to running-based CFA by showing the specificity of food suppression. Demonstration of CFA based on voluntary activity in non-deprived rats will contribute to basic research on learning and memory as an alternative technique for studying aversive conditioning with minimized discomfort in animals.

Running-based pica and taste avoidance in rats

Running in an activity wheel generates pica behavior (kaolin clay intake) in rats. Wheel running also results in Pavlovian conditioned avoidance of the taste solution consumed immediately before the running. Since pica has been considered a behavioral marker of nausea in rats, these findings suggest that wheel running induces nausea, which is the underlying physiological state for establishing taste avoidance. This article reports a replication of running-based pica in rats (Experiment 1) and concurrent demonstrations of running-based pica and taste avoidance in the same animals (Experiments 2 and 3). Also shown is that pica does not alleviate running-based taste avoidance (Experiment 3). Another finding is that pica is generated by a nausea-inducing lithium chloride injection but not by a pain-inducing hypertonic saline injection (Experiment 4). These results, when taken together, support the hypothesis that pica behavior generated by wheel running reflects nausea in rats.