Social avoidance behavior in male tree shrews and prosocial behavior in male mice toward unfamiliar conspecifics in the laboratory

Adult male tree shrews vigorously defend against intruding male conspecifics. However, the characteristics of social behavior have not been entirely explored in these males. In this study, male wild-type tree shrews(Tupaia belangeri chinensis)and C57 BL/6 J mice were first allowed to familiarize themselves with an open-field apparatus. The tree shrews exhibited a short duration of movement(moving) in the novel environment, whereas the mice exhibited a long duration of movement. In the 30 min social preference-avoidance test, target animals significantly decreased the time spent by the experimental tree shrews in the social interaction(SI)zone, whereas experimental male mice exhibited the opposite. In addition, experimental tree shrews displayed a significantly longer latency to enter the SI zone in the second 15 min session(targetpresent) than in the first 15 min session(targetabsent), which was different from that found in mice.Distinct behavioral patterns in response to a conspecific male were also observed in male tree shrews and mice in the first, second, and third 5 min periods. Thus, social behaviors in tree shrews and mice appeared to be time dependent. In summary,our study provides results of a modified social preference-avoidance test designed for the assessment of social behavior in tree shrews. Our findings demonstrate the existence of social avoidance behavior in male tree shrews and prosocial behavior in male mice toward unfamiliar conspecifics. The tree shrew may be a new animal model, which differs from mice, for the study of social avoidance and prosocial behaviors.

Cymbopogon citratus aqueous leaf extract attenuates neurobehavioral and biochemical changes induced by social defeat stress in mice

Objective:Psychosocial stress has been implicated in the genesis of psychiatric disorders such as memory deficits,depression,anxiety and addiction.Aqueous leaf extract of Cymbopogon citratus(CYC)otherwise known as lemongrass tea has antidepressant,anxiolytic and anti-amnesic effects in rodents.This study was designed to evaluate if C citratus could reverse the neurobehavioral and biochemical derangements induced by social defeat stress(SDS)in the resident/intruder paradigm.Methods:Intruder male mice were divided into five groups(n=7):group 1 received saline(10 mL/kg,p.o.;non-stress control),group 2 also received saline(10 mL/kg,p.o.;SDS control)while groups 3-5 had C.citratus(50,100 and 200 mg/kg,p.o.)daily for 14 d.The SDS was carried out 30 min after each treatment from day 7 to day 14 by exposing each intruder mouse in groups 2-5 to a 10 min confrontation in the home cage of an aggressive resident counterpart.The neurobehavioral features(spontaneous motor activity-SMA,anxiety,memory,social avoidance and depression were then evaluated.The concentrations of nitrite,malondialdehyde and glutathione as well as acetylcholinesterase activity in the brain tissues were also determined.Results:C.citratus(50,100 and 200 mg/kg)attenuated hypolocomotion,heightened anxiety,depressive-like symptom,memory deficit and social avoidance induced by SDS.The altered levels of oxidative stress and acetyl-cholinesterase in SDS-mice were positively modulated by C.citratus.Conclusion:The results of this study suggest that C.citratus might mitigate psychosocial stress-induced neurologic diseases in susceptible individuals.