Social Isolation Model: A Noninvasive Rodent Model of Stress and Anxiety

Summary

Presented here is a social isolation (SI)-induced anxiety mouse model that utilizes wild type C56BL/6J mice to induce stress and anxiety-like behavior with minimal handling and no invasive procedures. This model reflects modern life patterns of social isolation and is ideal for studying anxiety and related disorders.

Abstract

Anxiety disorders are one of the leading causes of disability in the United States (US). Current treatments are not always effective and less than 50% of patients achieve full remission. A critical step in developing a novel anxiolytic is to develop and utilize an animal model, such as mice, to study pathological changes and test drug target(s), efficacy, and safety. Current approaches include genetic manipulation, chronic administration of anxiety-inducing molecules, or the administration of environmental stress. These methods, however, may not realistically reflect anxiety induced throughout daily life. This protocol describes a novel anxiety model, which mimics the intentional or unintentional patterns of social isolation in modern life. The social isolation-induced anxiety model minimizes perceived distractions and invasiveness and utilizes wild type C57BL/6 mice. In this protocol, 6- to 8-week-old mice (male and female) are singly housed in opaque cages to visually block the external environment, such as neighboring mice, for 4 weeks. No environmental enrichments (such as toys) are provided, bedding material is reduced by 50%, any treatment of drug is administered as an agar form, and the exposure/handling of the mice is minimized. Socially isolated mice generated using this protocol exhibit greater anxiety-like behavior, aggression, as well as decreased cognition.

Introduction

Anxiety disorders represent the largest class and burden of mental diseases in the United States (US), with related annual costs exceeding US$42 billion^1,2,3. In recent years, anxiety and stress have heightened the prevalence of suicide and suicide ideation by over 16%⁴. Patients with chronic diseases are especially vulnerable to unintended secondary effects of mental distress or reduced cognitive function⁵. Current treatments for anxiety include psychotherapy, medications, or a combination of both⁶. Howe....

Protocol

All animal experiments are performed according to the protocols approved by the University of Southern California (USC) Institutional Animal Care and Use Committee (IACUC), and all methods are carried out in accordance with relevant guidelines, regulations, and recommendations.

1. Animals

1. Obtain approval from appropriate animal care committees for the study.
2. Set the vivarium to a dark-light 12 h cycle with controlled temperature and humidity between 24 ± 2 °C and 50%-60%, respectively.
3. Obtain male and/or female wild type C57BL/6 mice aged 6-8 weeks. After stratifying the animals by sex, rando....

Results

All representative results and figures were modified from our recent publications^22,23. To evaluate the effects of social isolation on anxiety and exploratory behavior, EPM and OF tests were performed 24 h following the end date of the 4 week social isolation period. Socially isolated mice spent significantly less time in the open arm (1.28 ± 0.17 min) compared to the control (2.31 ± 0.27 min), and a significantly longer time in the closed arm (3.31 ± 0.27 min) c.......

Discussion

Critical steps in the protocol include properly setting up the social isolation cages (i.e., wrapping of opaque bags and reducing the amount of bedding), minimizing the handling and disturbance of mice throughout the isolation period, and making sure the mice obtain and consume the agar with drug completely. It is critical that the vivarium or housing condition is maintained at a constant temperature and humidity, as well as minimized external interferences. Significant effort should be placed toward reducing as.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Black Plastic Bags	Office Depot	791932	24" x 32"
Elevated Plus Maze	SD Instruments	NA	Black color
Open Field enclosure	SD Instruments	NA	White color
Select Agar	Invitrogen	30391-023
Square cotton for nesting (nestlet)	Ancare Corporation	NC9365966	Divide a 2" square piece into 4 pieces to create a 1" square piece for isolation group
Sucrose	Sigma	S1888-1KG
Weigh boat	SIgma	HS1420A	Small, square white polystyrene