Practical rat tickling: Determining an efficient and effective dosage of heterospecific play

摘要

Laboratory rats may experience stress during handling which can reduce their welfare. Rat tickling, a handling technique that mimics aspects of rat rough-and-tumble play, has been found to induce positive affect based on production of 50-kHz ultrasonic vocalizations (USVs). However, current protocols for rat tickling are time-intensive, making implementation difficult. Our objective was to determine a time-efficient and effective dosage of rat tickling that could be practically implemented in the laboratory. We hypothesized that affect and handling can be improved by short, daily doses of tickling within a 5-day work week. Long-Evans rats (N = 72) of both sexes, housed in pairs were sampled. Each pair was randomly assigned a tickling duration (15, 30 or 60 s per rat) and frequency (1, 3, or 5 days). After the final day of tickling, rats were tested for ease of, and reaction to, handling via an intraperitoneal injection of saline following a tickling session for their assigned duration. On test day, we measured production of USVs, home cage behavior (60 min before/after testing), approach behavior (30 s before/after testing), and fecal corticosterone. Periods before and after testing measured anticipatory and reactionary responses, respectively. In cage behaviors included social play, activity, and location. Approach behaviors included indicators of fear or anxiety such as rearing, location, and contact with the hand. Data were analyzed using general linear models. We found that 3-day rat tickling was most efficient and effective as it produced a higher rate of 50-kHz USVs before and during tickling (p & 0.0001), and rats played more and were less inactive in their cage for the hour before tickling and injection (p & 0.003) compared to 1-day of rat tickling, but there was no difference between 3- and 5-days of tickling. Only one outcome (play behavior after tickling) showed more positive results after 5- vs 3-days of tickling (p = 0.002). Tickling duration did not impact any outcome measures (p & 0.05). Neither tickling duration nor frequency impacted approach behavior, injection duration, or fecal corticosterone (p & 0.05). In conclusion, a time-efficient and effective rat tickling dosage was identified to be 15 s for 3-days before any potentially aversive procedures are applied. This conclusion is based on increased 50-kHz USVs (a measure of positive affect) and positive anticipatory behavior, including play. Overall, our results suggest that minimal rat tickling can effectively habituate rats to handling and prepare them for research procedures within a work week.