Social Threat-Safety Test Uncovers Psychosocial Stress-Related Phenotypes

Summary

The social threat-safety test allows a simultaneous assessment of social avoidance development as a measurement of aversive conditioned learning and social threat-safety discrimination ability, both utilized to identify stress-susceptible and stress-resilient individuals within a single group of chronically socially defeated male mice.

Abstract

Social stress is a major cause of the development of mental disorders. To enhance the translational value of preclinical studies, social stress experience and its behavioral impact on mice should be comparable to humans. Chronic social defeat (CSD) utilizes a type of social stress involving physical attacks and sensory threats to induce mental dysfunctions resembling human affective disorders. To strengthen the psychosocial component of CSD, a 10-day CSD protocol was applied in which daily physical attacks are standardized to three 10 s episodes followed by a 24 h sensory phase. After the 10^th sensory phase, the CSD protocol is followed by a refined behavioral assay called the social threat-safety test (STST). Post-stress behavioral assays need to determine how and to what extent the social stressor has influenced behavior. The STST allows chronically socially defeated male mice to interact with 2 novel male individuals (social targets): one social target from the attacking strain encountered during the CSD days and the other from a novel strain. Both are presented simultaneously in different compartments of a three-chambered test arena. The test enables a simultaneous assessment of social avoidance development to measure successful aversive conditioned learning and social threat-safety discrimination ability. The development of social avoidance towards both strains reflects a generalized aversive response and thus, a measurement of stress susceptibility. Meanwhile, the development of social avoidance towards only the attacking strain reflects threat-safety discrimination and thus, a measurement of stress resilience. Finally, the absence of social avoidance towards the attacking strain reflects impaired aversive conditioned learning. The protocol aims to refine the currently used mouse models of stress susceptibility/resilience by including translational criteria, specifically threat-safety discrimination and aversive response generalization, to categorize a single group of chronically socially defeated animals into resilient and susceptible subgroups, eventually advancing future translational approaches.

Introduction

Stress is defined as the disruption of homeostasis caused by physical or psychological stimuli¹. Stress is a well-known major risk factor for the development of mental disorders such as post-traumatic stress disorder, depression, and anxiety^2,3. In particular, social stress is considered a major risk factor for the development of stress-related mental disorders⁴. One type of social stress that has gained particular importance in research is social subordination stress⁵. Mice, like humans, are capable of a rich set of social behavior

Protocol

All procedures were performed in accordance with the European Communities Council Directive regarding the care and use of animals for experimental procedures and were approved by local authorities (Landesuntersuchungsamt Rheinland-Pfalz). Figure 1 represents a schematic timeline.

1. Treatment

1. Animals of interest: Obtain C57BL6/J male mice at 7 weeks of age, and upon arrival, single-house in a temperature- and humidity-controlled facility on a 12 h light-dark cycle (lights on: 8:00; lights off: 20:00; 23 °C; 38% humidity) with food and water ad libitum.
2. Chronic social ....

Results

Social interaction index as a measurement of aversive conditioned response
A social interaction index ≥1 reflects greater social interaction with the respective social target compared to the exploration of the empty mesh enclosures. Under baseline conditions, defined here as having neither appetitive nor aversive experience with the characterizing traits of a specific strain (here both social targets to the control group and the 129/Sv social target to the treatment group), intact sociability.......

Discussion

The behavioral protocol here describes the Social Threat-Safety Test, used to divide a single group post-CSD treatment into three different subgroups, serving as a method to investigate the underlying biology of stress susceptibility and resilience and to test potential therapies. The biological context and technical details need to be carefully considered to guide a thorough experimental design.

Different housing conditions can alter aggression sociability levels, potentially influencing resu.......

Materials

Name	Company	Catalog Number	Comments
Arenas	Noldus, Sociability cage, Wageningen, the Netherlands	https://www.noldus.com/applications/sociability-cage	Three-chambered, rectangle in shape with a total size of 60 cm x  40 cm, made of acrylic transparent walls and smooth floors
Camera for video recording	Basler AG, Germany An der Strusbek 60-62 22926 Ahrensburg	ace Classic acA1300-60gc	If using automatic detection program, make sure cameras are compatible
Camera objective	KOWA Kowa Optimed Deutschland GmbH Fichtenstr. 123 40233 Duesseldorf: LMVZ4411 | 1/1.8" 4.4~11mm Varifokal Objektiv	Part-No. 10504
Detection program/Timer	Noldus, EthoVision-XT, Wageningen, the Netherlands	https://www.noldus.com/ethovision-xt	Detection can be achieved either manually (using a timer or a software for manual scoring) or automatically
Housing cages	ZOONLAB GmbH, Hermannstraße 6, 44579 Castrop-Rauxel	3010010	Type 2 cages: 265 mm x 205 mm x 140 mm (l x w x h) i.e. 360 cm² bottom area. Made of Polycarbonate (Makrolone©) and Polysulfone. Lids are made of stainless steel. European standard cages for up to 5 mice (20–25 g). Autoclavable up to 134 °C
Mesh enclosures	Part of the Arena Package: Noldus, Sociability cage, Wageningen, the Netherlands	https://www.noldus.com/applications/sociability-cage	Small acrylic or metal cage-like with a diameter of 100 mm and a height of 200 mm with openings of a 10 mm in size. Two mesh enclosures per arena would work but four is preferable (see point 2.5 in protocol)
Mesh wall	selfmade	N/A	Acrylic or metal, one for each cage. Size depends on cages used. The walls must not allow the two animals to have a physical contact
Social targets: Mice of the strains CD-1 and 129/Sv; retired male breeders	Mice provided by Charles River: Strain name: CD-1®IGS Mouse 129S2/SvPasCrl	Crl:CD1(ICR); 129S2/SvPasCrl	CD-1 and 129/Sv retired male breeders, single-housed, novel (unknown) conspecifics to the animals of interest. If retired male breeders are not available then males older than 1 year from both strains would suffice