April 19, 2017

Handling-Associated Stress Affects Test Performance in Mice

Research shows that the way in which mice are handled during research experiments can alter results.
By Karen Todd-Jenkins, VMD
According to researchers at the University of Liverpool, picking mice up by their tail is a relatively common practice in laboratory settings. However, this type of handling stresses the mice, which can adversely affect their behavior and test performance. The end result is that data from these studies may be unreliable because of stress-associated alterations in performance. Their research was published recently in Nature Scientific Reports.
 
Prior to the experiment, mice arriving at the laboratory were divided into three groups. During cage cleaning, Group 1 mice were transferred to clean cages by picking them up by the tail (tail handling). Group 2 mice were transferred using an acrylic handling tunnel (present in all the cages) that didn’t require direct touching by the handlers, and Group 3 mice were transferred using a cupped hand.

This initial handling continued for several weeks to accustom the mice in each group to the selected form of handling.
 
In the experiment, female mice were presented with the scent of male mouse urine repeatedly over the course of several days. The scent induced the expected level of interest (ie, approach and investigation) in the mice initially. After the initial response to the “novel” stimulus waned, the female mice were exposed to a different scent to see if they could discern the difference between the previous scent and the new one (as indicated by renewed interest and investigation of the new scent).

During the experiment, the mice were transferred to the location of the new scent via the method that had been used since the mice arrived (tail handling, tube, or cupped hand). Their responses were observed and recorded.
 
The experimenters also assessed whether the location of the scent (near the edges or in the center of the test arena) affected the willingness of the mice to explore the scent. 
 
Results and Discussion
The researchers reported that mice subjected to tail handling were disinterested in investigating the test stimuli and reluctant to explore the test area. Some of them refused to sniff the scent at all during any of the repeated exposures. Further, tail-handled mice were anxious, more cautious, and reluctant to move into the center of the arena. These mice were also less willing to interact with handlers.

In contrast, mice that were handled using a handling tunnel or cupped hand performed better, as evidenced by their willingness to explore the new area and the novel scents. These mice performed similarly in terms of willingness to explore, but mice handled using a tunnel did better overall than mice in either of the other two groups (sniffing the scent longer and performing more consistently). 
 
The authors note, “We show that the use of tail handling creates a substantial interference with test responses, as animals failed to show free exploration of the test arena or pay sufficient attention to urine test stimuli. This led to very poor performance measures in a test that should have been easy to perform.” In contrast, mice that were not subjected to aversive handling readily explored the test arena and performed better.
 
In addition to improved handling being an animal welfare issue, this study suggests that replicating test results in other studies and between different groups of mice is complicated when mice are tail-handled, as this handling skews the test results and produces data that can be misleading.
 
The authors further caution that assessment of physiologic parameters affected by stress, such as glucose tolerance, should also be interpreted in light of how the mice were handled during the investigation.

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