Rat tickling: A systematic review of applications, outcomes, and moderators

Abstract

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.

Laboratory Animal Welfare Meets Human Welfare: A Cross-Sectional Study of Professional Quality of Life, Including Compassion Fatigue in Laboratory Animal Personnel

“…Considering these contrary effects, it is difficult to make general recommendations for personnel on these specific human-animal interactions in terms of human welfare. In terms of animal welfare, petting may be beneficial for some animals, such as dogs (32), but negative for others such as naïve laboratory rats, in which case rat tickling is recommended instead (33). Despite this, positive human-animal interactions should be beneficial for animal welfare although more research is needed in this area (34,35).…”

Tickling, a Technique for Inducing Positive Affect When Handling Rats

“…In contrast, abundant evidence supports the conclusion that tickling, a handling technique that mimics aspects of the playful rough-and-tumble behavior of rats, is a robustly beneficial form of social contact, especially for juvenile rats 10 11 12 13 . Rats are highly social mammals, which is clear from observing the time they spend playing together as juveniles 14 and their strong motivation to re-establish and maintain social contact with conspecifics 15 16 17 .…”

“…This concept was originally developed as a model for investigating the neurobiological basis of positive affective states evoked by social play behavior 7 . Since then, rat tickling has been used in over 56 different experiments, 22 of which compared tickling to other handling techniques 13 .…”

Assessing Affective State in Laboratory Rodents to Promote Animal Welfare—What Is the Progress in Applied Refinement Research?

“…While mice do vocalize in social contexts, examples are mating songs of male mice, social vocalization of female mice, and distress calls of mice pups [41], analyses of mouse vocalization have not revealed frequencies or patterns allowing for unambiguous discrimination between positive or negative affective states. In rats, ultrasonic vocalization has been used successfully in refinement research, for example, to prove the negative effects of gradual-fill CO 2 killing in rats [42] or to set out the welfare enhancing effects of rat tickling (heterospecific play) (e.g., [43,44]). Contrary to rats, in mice, no vocalization indicative for negative affective states was detectable when different inhalants for euthanasia were tested [45].…”