Helping-Like Behaviour in Mice Towards Conspecifics Constrained Inside Tubes

Abstract

Prosocial behaviour, including helping behaviour, benefits others. Recently, helping-like behaviour has been observed in rats, but whether it is oriented towards rescue, social contact with others, or other goals remains unclear. Therefore, we investigated whether helping-like behaviour could be observed in mice similar to that in rats. Because mice are social animals widely used in neuroscience, the discovery of helping-like behaviour in mice would be valuable in clarifying the psychological and biological mechanisms underlying pro-sociability. We constrained mice inside tubes. Subject mice were allowed to move freely in cages with tubes containing constrained conspecifics. The subject mice released both cagemates and stranger mice but did not engage in opening empty tubes. Furthermore, the same behaviour was observed under aversive conditions and with anesthetised conspecifics. Interestingly, hungry mice opened the tubes containing food before engaging in tube-opening behaviour to free constrained conspecifics. Mice showed equal preferences for constrained and freely moving conspecifics. We demonstrated for the first time that mice show tube-opening behaviour. Furthermore, we partly clarified the purpose and motivation of this behaviour. An effective mouse model for helping-like behaviour would facilitate research on the mechanisms underlying prosocial behaviour.

Figure 1

Training for opening the paper lid and tube-opening behaviour test. (A) Sample picture and schematic diagram of training for opening the paper lid. One side of the 50-mL tube was closed with a paper lid and the other with a plastic lid. (B) Sample picture and schematic diagram of the mouse waiting for release from the 50 mL tube. A 1-cm-diameter hole in front of the mouse and a paper lid at the back. (C) A sample image of the tube, containing the mouse, covered at the back with a paper lid. (D) Sample picture and schematic diagram of the tube-opening behaviour test in the new home cage. A tube containing the cagemate mouse on one side and an empty tube on the other side. (E) Sample picture during the test of tube-opening behaviour. The test mouse freely moves in the cage. (F) Tube-opening behaviour test for constrained cagemate: latency to paper lid-opening in each trial. All data are presented as box plots. The p values were calculated uisng one-way repeated measures ANOVA (F). n = 14 animals.

Figure 2

Tube-opening behaviour test for both cagemate and stranger mice, and tube-opening behaviour test for anesthetised cagemate mice. (A) Schematic diagram of the test. Tube-opening behaviour test for cagemate and stranger mice: time spent in the area (B) and latency to lid-opening (C). (D) Individual latency to lid-opening in the tube-opening behaviour test for both cagemate and stranger mice. (E) Schematic diagram of this test. (F) Tube-opening behaviour test for anesthetised cagemate mice: time spent in the anesthetised cagemate area or empty area. (G) Comparison of the latency to lid-opening for an anesthetised and a non-anesthetised mouse. All data are presented as box plots. The p values were calculated using paired t-test (B,F), Wilcoxon signed-rank test (C), and one-way repeated measures ANOVA (G). n = 9 animals per test.

Figure 3

Tube-opening behaviour test in hungry and non-hungry states. (A) Upper row: Sample picture of the 50-mL tube containing food. It is closed with a paper lid. Lower row: sample picture during the test of tube-opening behaviour in the hungry state. The tube containing the cagemate is located on the left side and the tube containing the food on the right side. The test mouse moves freely around the cage. (B) Schematic diagram of this test. The cagemate area refers to the half of the home cage with the tube containing the cagemate mouse, and the feed area refers to the half of the home cage with the tube containing the food. Tube-opening behaviour test for cagemate versus feed in the food-deprived state: time spent in the area (C) and latency to lid-opening (D). Tube-opening behaviour test for cagemate versus feed in the non-food deprived state: time spent in the area (E) and latency to lid-opening (F). All data are presented as box plots. The p values were calculated using paired t-test (C,E) and the Mann-Whitney’s U-test (D,F). n = 11 animals per test.

Figure 4

Tube-opening behaviour test under aversive conditions. (A) Schematic diagram of this test. Half of the home cage contains wet bedding and the other half contains dry, normal bedding. Tube containing the cagemate mouse on the wet bedding. (B) Tube-opening behaviour test for cagemate under the aversive condition: time spent in the area. (C) Average speed of the test mouse in each bedding. (D) Comparison of the latency to lid-opening when the tube contains the cagemate is placed on wet or normal bedding. (E) Latency to lid-opening in various conditions of the tube-opening behaviour test. All data are presented as box plots. (E) Statistical significance is represented by top bars: *p < 0.05. The p values were calculated using paired t-test (B,C) and one-way repeated measures ANOVA (D,E). n = 9 animals per test.

Figure 5

Preference tests for constrained cagemate and non-constrained cagemate mice in the social interaction test apparatus. (B) Schematic diagram of the apparatus of this experiment. Two transparent cages [(a), and (b)] are placed at both ends of a rectangular apparatus, and half of the area of the apparatus is taken as the respective area [area (a) and area (b)]. A radius of 20 cm around the transparent cage was set around the cage [around cage (a) and around cage (b)]. (B) Sample picture of the transparent cages containing constrained and non-constrained cagemates. (C) Test schedule. For each mouse, four tests were conducted according to the contents of the table. Cagemates in each state were placed in transparent cages (a) and (b). Preference tests for constrained cagemate and intact mice: time spent around the cage (D), and preference index defined as (time spent around cage (a))/(time spent around cage (a) + time spent around cage (b)). All data are presented as box plots. The p values were calculated using Wilcoxon signed-rank test (D) and one-way ANOVA (E). n = 16 animals per trial.