An Unpredictable Chronic Mild Stress Protocol for Instigating Depressive Symptoms, Behavioral Changes and Negative Health Outcomes in Rodents

Summary

The unpredictable chronic mild stress (UCMS) protocol is a validated method for studying behavioral and physiological changes associated with chronic stress and depressive symptoms. Eight weeks of imposition of the UCMS protocol induces behavioral changes and poor health outcomes in rodents of either gender.

Abstract

Chronic, unresolved stress is a major risk factor for the development of clinical depression. While many preclinical models of stress-induced depression have been reported, the unpredictable chronic mild stress (UCMS) protocol is an established translationally-relevant model for inducing behavioral symptoms commonly associated with clinical depression, such as anhedonia, altered grooming behavior, and learned helplessness in rodents. The UCMS protocol also induces physiological (e.g., hypercortisolemia, hypertension) and neurological (e.g., anhedonia, learned helplessness) changes that are clinically associated with depression. Importantly, UCMS-induced depressive symptoms can be ameliorated through chronic, but not acute, treatment with common SSRIs. As such, the UCMS protocol offers many advantages over acute stress protocols or protocols that utilize more extreme stressors. Our protocol involves randomized, daily exposures to 7 distinct stressors: damp bedding, removal of bedding, cage tilt, alteration of light/dark cycles, social stresses, shallow water bath, and predator sounds/smells. By subjecting rodents 3-4 hr daily to these mild stressors for 8 weeks, we demonstrate both significant behavioral changes and poor health outcomes to the cardiovascular system. This approach allows for in-depth interrogation of the neurological, behavioral, and physiological alterations associated with chronic stress-induced depression, as well as for testing of new potential therapeutic agents or intervention strategies.

Introduction

Depressive mental illness is a complex neurological disorder that is currently recognized as a leading cause of disability and disease burden worldwide. The NIMH reports that approximately 12% of Americans suffer from clinical depression, with twice as many women affected versus men¹. In the US alone, depression accounts for billions of dollars direct healthcare costs and an estimated $193 billion more in indirect costs (lowered earnings and lost productivity)². Symptoms of depression include anhedonia, changes in weight and sleep cycles, decreased physical activity and personal hygiene, feelings of hopelessness or guilt, and/or reoccurring thoug....

Protocol

All procedures described below have been reviewed and approved by the Institutional Animal Care and Use Committee at the West Virginia University Health Sciences Center.

1. Selection of Animal Model 

NOTE: Most commonly used species in the UCMS model include Sprague Dawley, and Wistar rats and the BALB/cJ mouse; other murine models have shown limited efficacy (DBA/2, C57BL/6).  However, careful consideration should be given to the particular mouse or rat strain of choice, as the genetic background and susceptibility to environmental stressors vary widely among species and have been shown to be cri....

Results

An example of the schedule for one week following the UCMS procedure is shown in Table 1. Each week, stressors were randomized to prevent acclamation and to ensure unpredictability of the stress challenge each day.

Measures of Depressive like Behaviors

Following 8 weeks of UCMS, there were significant alterations to both behavioral and physiological outcomes in chronically stressed rodents relative to their non-stressed control strains. Development .......

Discussion

Extensive clinical and epidemiological evidence has indicated that chronic stress is one of the most potent precipitating factors for depression. Repeated exposure to stressors may potentiate individual vulnerability to depression and other neuropsychiatric disorders as a consequence of the psychological and physical demands within the body that accumulate over time. The use of validated preclinical animal models offers a valuable translational tool for studying depression and comorbid diseases. Firstly, an ideal animal .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Temporary animal cages with lids			Provided by your animal care facility
Rodent bedding			Provided by your animal care facility
Predator fur or urine			Provided by your animal care facility
Rodent cage drinking bottles			Provided by your animal care facility
1,000 ml graduated cylinder	variable	variable	This is optional.  Any container from which a known quantiity of water can be poured will be appropriate
Wooden blocks cut from 2x4	variable	variable	8 inch sections are cut to facilitate cage tilt procedures
Soft paper towels			Provided by your institution
Small spray bottle	Walmart		100-200 ml volume is sufficient, used for sucrose splash test
Medium (mice) or large (rats) plastic tubs for swim testing	Walmart	variable	Should be of sufficient depth that the animals cannot touch bottom (e.g., 2 feet)