IntroductionRats initially fear humans which can increase stress and impact study results. Additionally, studying positive affective states in rats has proved challenging. Rat tickling is a promising habituation technique that can also be used to model and measure positive affect. However, current studies use a variety of methods to achieve differential results. Our objective was to systematically identify, summarize, and evaluate the research on tickling in rats to provide direction for future investigation. Our specific aims were to summarize current methods used in tickling experiments, outcomes from tickling, and moderating factors.MethodsWe systematically evaluated all articles about tickling identified from PubMed, Scopus, Web of Science, and PsychInfo. Our inclusion criteria were publication in a peer-reviewed journal and collection of original, empirical data on rats using the handling method of tickling. One researcher extracted information from each article. Bias was assessed by 2 investigators using the SYRCLE bias assessment tool.ResultsWe identified 32 articles (56 experiments) published in peer-reviewed journals about rat tickling for inclusion. A wide variety of strains, sexes, and ages of rats were included. The most common method used for tickling was cycling through 15 seconds of tickling and 15 seconds of rest for 2 minutes for 3 to 5 days. Experiments with a control for tickling (N = 22) showed that tickling increases positive vocalization, approach behavior, decreases anxiety measures, improves handling, and in some cases decreases stress hormones. Tickling juvenile, individually housed rats with a trait predisposition to respond more positively to tickling, results in the most positive outcomes. Methods to reduce bias were insufficiently reported.ConclusionsWe conclude that tickling is a promising method for improving rat welfare and investigating positive affect. However, the establishment of tickling best practices is essential as the outcomes from tickling can be moderated by several factors.

No abstract

high level throughout data collection. We documented the number of restraint attempts to assess rat handleability. A restraint attempt was defi ned as when the researcher's fi rst two fi ngers touched the animal's neck and ended when the rat was either lifted up or the fi ngers stopped touching the neck. The preliminary results indicate that all tickled rats required fewer restraint attempts than control rats, and low-calling rats reared less during both approach tests, a behavior indicative of comfort and exploration. These fi ndings support previous research, which has shown that tickling rats can help alleviate their stress and improve their welfare. Animal welfare and the effects of the human-animal bond are becoming increasingly important to researchers and the public. Animal use in biomedical research is indispensable and inevitably creates stressful situations for the animals. One way to mediate this stress and improve rat welfare is by using a handling technique called tickling. Tickling, which mimics rat rough-and-tumble play, reduces fear of humans and stress of injections (Cloutier & Newberry, 2007; Cloutier, Panksepp, & Newberry, 2012). When rats play or are tickled, they elicit ultrasonic vocalizations (USV), which cannot be heard by humans. These vocalizations can be recorded and analyzed using specialized sound equipment and software. USVs of 50 kHz indicate positive emotions, while 20-kHz USVs indicate negative emotions. Tickling has been shown to benefi t laboratory rats, but some individuals respond more positively to tickling and may receive greater benefi ts. Additionally, welfare improvements have yet to be empirically validated in pet rats. Research advisor BriannaThirty-six female pet store rats were sampled across two replicates. During each replicate, rats were randomly placed into one of three cages. One cage, designated as the control group, received standard, minimal handling throughout the study. After 3-4 days of acclimation, rats were tickled for 3 consecutive days by the researcher and their USVs were recorded. Based on the total number of positive vocalizations produced, the rats were then split into high-and low-calling cages. After 4 more days of being tickled by the employees, rats were evaluated using an unfamiliar approach and restraint test to evaluate fear behaviors and ease of restraint. We began the approach test by placing each rat in a glass tank opposite from an unfamiliar hand. After one minute had elapsed, the unfamiliar researcher picked up the rat to manually restrain it, using a technique commonly used at veterinary hospitals and in laboratories.After 30 seconds of restraint, the rat was then placed back into the tank for an additional 1-minute approach test. These approach and restraint tests were video-recorded for later analysis by video coders blinded to the treatment groups. Reliability of the coders was tested using intraclass correlation and was maintained at a AGRICULTURE