The overall goal of this procedure is to elicit positive affect and reduce fear of humans in rats. This method can help improve the welfare of rats in animal science. It also provides a tool for investigating affective states at the behavioral and neurobiological levels.
The main advantages to tickling rats is that it is an efficient and practical way of eliciting positive affect, reducing fear, and improving welfare. People who are new to this method may not tickle vigorously enough when attempting to mimic aspects of rat rough and tumble play. A visual demonstration of this method helps researchers to apply it in a standardized way that's comparable across studies.
Remove the cage from the rack and place it on a countertop at a height that allows the handler to readily reach the entire area of the floor. To begin, put on any required personal protective equipment. Remove any obstacles from the home cage.
Then position a timer near the handling box where the handler can easily see it. To record vocalizations, suspend the microphone to the side of the handling box low enough to clearly capture the vocalizations from the rats in the box. Begin the tickling session with a 15-second release by placing a hand motionless on one side of the handling box.
If a rat solicits interaction by licking or nibbling the hand, move the hand away to initiate playful chasing of the hand by the rat. Follow the release with 15 seconds of tickling which is made up of a series of rapidly alternating dorsal contacts and pins. Rats typically utter a positive 50 kilohertz ultrasonic vocalizations when tickled.
Tickling is initiated by a dorsal contact with the fingertips moving vigorously on the nape of a rat's neck as commonly performed in human tickling. During the dorsal contact, the fingers of one hand should make light, brisk, and vigorous tickling motions on the nape of the rat's neck. Then flip the rat over with one hand by placing the thumb and middle finger under the rat's forelegs, lifting the rat and using a flick of the wrist to turn the rat onto its back.
Finally, hold the rat in this pinned position with moderate pressure for two to four seconds while using the fingertips to tickle the rat's stomach. During the pin, the rat should be held down gently and once again the fingers of one hand should make light, brisk, and vigorous tickling motions on the rat's stomach. Continue tickling by performing additional dorsal contacts and pins.
There should be about four to five dorsal contacts and pins per 15 seconds of tickling. Then perform three additional cycles of 15-second releases alternating with 15-second tickles of the same rat for a total of two minutes. For rats in pairs, the release period for one rat provides time to perform tickling of the other rat.
Replace the previously removed enrichment objects in the home cage. Finally, return the home cage containing the rats to the housing rack. In a representative experiment, rats are given IP saline injections daily for 10 days.
The rats that are tickled for two minutes immediately before and after saline injections produced more 50 kilohertz ultrasonic vocalizations than rats exposed to a passive hand. Rat responses to tickling before, after, or before and after restraint are compared. Rats from treatments that received tickling before restraint produced the most 50 kilohertz vocalizations before and during the procedure.
In the two minutes after the restraint procedure, all of the tickled rats produced more vocalizations than those that are not tickled. While attempting this procedure, it's important to remember that it mimics aspects of rat rough and tumble play. Tickles should be boisterous, playful, and somewhat unpredictable.
Rat ultrasonic vocalizations can be recorded in order to answer questions about rat affect and assess the effectiveness of your tickling technique.
