Noradrenergic system contributes to the maintenance of social hierarchy in mice

[Speaker] Yuiko Nishihara:1
[Co-author] Yuki Kurauchi:1, Hina Kawamoto:1, Risako Tanaka:1, Akinori Hisatsune:2, Takahiro Seki:1, Hiroshi Katsuki:1
1:Department of chemico-pharmacological sciences, graduate school of pharmaceutical sciences, Kumamoto university, Japan, 2:Priority organization for innovation and excellence, Kumamoto university, Japan

 Social hierarchy is one of the structure of population in animals, and it is affected by mental strength. Although various systems in the brain and peripheral tissues have been reported to contribute to the formation of social hierarchy, it is poorly understood whether noradrenergic system, which plays an important role in the stress-related behavior, affects the maintenance of social hierarchy. In this study, we investigated the effect of propranolol, a β-blocker, which is clinically used for the treatment of anxiety disorder, on the maintenance of social hierarchy in mice.
 To evaluate the formation of social hierarchy, we performed the tube test. Eight-weeks old male C57BL/6J mice were housed in groups of 4 for 2 weeks before tube test. In test days, pairs of mice were released at two ends of a tube (30 cm in length, 3 cm in diameter) and met at the middle, and the mouse that retreated first from the tube was designated as loser. For a group of 4 mice, all 6 pairs of mice were daily tested with a round robin design and ranks were determined by winning percentage. At five days of tube test, we started intraperitoneal administration of propranolol (10 mg/kg) to 1 mouse (rank1, rank2, rank3 or rank4 mouse) out of 4 mice and also performed tube test for 5 consecutive days.
 Propranolol had no effect on the winning percentage of rank1, rank3, and rank4 mice. On the other hand, the winning percentage of each mouse in the group which received propranolol administration to rank2 mouse dynamically changed. We also found that daily administration of saline to each mouse did not change the social hierarchy.
 Noradrenergic system contributes to the maintenance of social hierarchy in mice, and rank2 mice are susceptible to the change in noradrenergic activity. These results provide an evidence for understanding the mechanism of pathological social behaviors.

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