Further Evidence for 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.

Evaluating proxies for motion sickness in rodent

Motions sickness (MS) occurs when the brain receives conflicting sensory signals from vestibular, visual and proprioceptive systems about a person's ongoing position and/or motion in relation to space. MS is typified by symptoms such as nausea and emesis and implicates complex physiological aspects of sensations and sensorimotor reflexes. Use of animal models has been integral to unraveling the physiological causality of MS. The commonly used rodents (rat and mouse), albeit lacking vomiting reflex, reliably display phenotypic behaviors of pica (eating of non-nutritive substance) and conditioned taste aversion (CTAver) or avoidance (CTAvoi) which utilize neural substrates with pathways that cause gastrointestinal malaise akin to nausea/emesis. As such, rodent pica and CTAver/CTAvoi have been widely used as proxies for nausea/emesis in studies dealing with neural mechanisms of nausea/emesis and MS, as well as for evaluating therapeutics. This review presents the rationale and experimental evidence that support the use of pica and CTAver/CTAvoi as indices for nausea and emesis. Key experimental steps and cautions required when using rodent MS models are also discussed. Finally, future directions are suggested for studying MS with rodent pica and CTAver/CTAvoi models.

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.

A New Vestibular Stimulation Mode for Motion Sickness With Emphatic Analysis of Pica

Motion sickness (MS) was frequently introduced for rodents in research work through passive motion that disturbed vestibular signals in the presence of visual and aleatory, proprioceptive inputs. Inducement of MS in this way causes conflicting signals that activate intermixed neural circuits representing multimodal stimulation. From reductionism, a lab setup to elicit rat MS via vestibular stimulation was configured in the present study for MS study in connection with dissection of the central vestibular component causally underlying MS. The individual animal was blinded to light with a custom-made restrainer, and positioned at an inclination of 30° for otolith organs to receive unusual actions by gravitoinertial vector. Following a 2-h double-axis (earth–vertical) rotation involving angular acceleration/deceleration, a suit of behaviors characterizing the MS was observed to be significantly changed including pica (eating non-nutritive substance like kaolin), conditioned taste avoidance and locomotion (p < 0.05). Notably, for the statistical hypothesis testing, the utility of net increased amount of kaolin consumption as independent variables in data processing was expounded. In addition, Fos-immunostained neurons in vestibular nucleus complex were significantly increased in number, suggesting the rotation-induced MS was closely related to the vestibular activation. In conclusion, our work indicated that the present setup could effectively elicit the MS by disturbing vestibular signals in rat in the context of well-controlled proprioceptive inputs and lack of visual afference.