Models of Depression: Unpredictable Chronic Mild Stress in Mice

Mathieu Nollet1, Anne‐Marie Le Guisquet2, Catherine Belzung2

1 Lilly Centre for Cognitive Neuroscience, Eli Lilly and Company, Windlesham, Surrey, United Kingdom, 2 INSERM 930, UFR Sciences et Techniques, Tours, France
Publication Name:  Current Protocols in Pharmacology
Unit Number:  Unit 5.65
DOI:  10.1002/0471141755.ph0565s61
Online Posting Date:  June, 2013
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Abstract

Major depression is a complex psychiatric disorder characterized by affective, cognitive, and physiological impairments that lead to maladaptive behavior. The high lifetime prevalence of this disabling condition, coupled with limitations in existing medications, make necessary the development of improved therapeutics. This requires animal models that allow investigation of key biological correlates of the disorder. Described in this unit is the unpredictable chronic mild stress mouse model that is used to screen for antidepressant drug candidates. Originally designed for rats, this model has been adapted for mice to capitalize on the advantages of this species as an experimental model, including inter‐strain variability, which permits an exploration of the contribution of genetic background, the ability to create transgenic animals, and lower cost. Thus, by combining genetic features and socio‐environmental chronic stressful events, the unpredictable, chronic mild stress model in mice can be used to study the etiological and developmental components of major depression, and to identify novel treatments for this condition. Curr. Protoc. Pharmacol. 61:5.65.1‐5.65.17 © 2013 by John Wiley & Sons, Inc.

Keywords: major depression; animal model; antidepressants

     
 
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Table of Contents

  • Introduction
  • Basic Protocol 1: Unpredictable Chronic Mild Stress (UCMS) Test in Mice
  • Basic Protocol 2: Assessment of Self‐Directed Activity and Anhedonia in Mice
  • Commentary
  • Literature Cited
  • Figures
  • Tables
     
 
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Materials

Basic Protocol 1: Unpredictable Chronic Mild Stress (UCMS) Test in Mice

  Materials
  • BALB/c mice (64), aged 8 weeks at the beginning of the experiment (e.g., Elevage Janvier)
  • Food pellets and water ad libitum
  • Stressors (see Table 5.65.1) including:
    • CD of various recordings of birds of prey cries lasting ∼10 min (at ambient level); these CDs can be purchased from a variety of commercial suppliers, such as http://www.wildtones.com or http://www.amazon.com
    • Soiled sawdust of rats from the same or previous day (with feces and urine)
    • Clock for changing the light/dark cycle for the stressed animals with a minimum accuracy of 30 min
    • Spruce sawdust
  • Fluoxetine (e.g., Sequoia Research Products, cat. no. SRP01950f) or imipramine (e.g., Sigma‐Aldrich, cat. no. I0899) diluted in saline solution (NaCl, 9 g/liter)
  • At least two different sound‐proof rooms in animal facilities with a stable environment (inverted 12 hr light/dark cycle, temperature 22°C ± 1°C, humidity 55 ± 10%); one room is used to house stressed mice and one room for nonstressed, control mice
  • Behavioral testing room
  • 32 individual cages for the stressed mice
  • Six to eight cages for the nonstressed mice (four to five mice per cage) with two shelters and one small tube (10‐cm length × 6.5‐cm i.d.) in each cage
  • Plastic restraint tubes closed at each end but enabling air circulation via small holes (length 6.5 cm × internal diameter 3.7 cm; see Fig. )
  • Environmental enrichment (shelters and tubes)
  • Precision balance 0.1 mg
  • 1‐ml syringes with 26‐G. 1/2‐in. needles for intraperitoneal (i.p.) injections
    Table 5.5.1   MaterialsExperimental Stressors

    Stressor Description
    Social stress Each mouse is placed in an empty cage previously occupied by another individual
    Cage change Each mouse is placed in the empty cage of another individual, and then returned to its original cage
    Sawdust change In the beginning of the UCMS protocol, the sawdust is changed 2 to 3 times per 24 hr, and up to 6 times per 24 hr at the end of the UCMS regimen. It is also possible to replace clean sawdust by soiled sawdust coming from control mice. The volume of each sawdust change is 250 ml (measured with a beaker).
    Without sawdust The sawdust is removed during 1 to 6 hr
    Damp sawdust Place 125 ml water in each cage. The period of damp sawdust can range from 1 to 6 hr.
    “Bath” The sawdust of each cage is removed and replaced by about 125 ml water at 20°C (about 1 cm water) for 15 to 30 min.
    Cage tilting Tilt the cages backwards (45 degrees) during 1 to 4 hr
    Rat feces About 60 ml of rat sawdust is deposited in each cage for a period of 1 to 2 hr
    Restraint stress The mice are kept in closed and ventilated tubes (6.5‐cm length × 3.7‐cm i.d.) for 15 to 30 min (mice have the possibility to turn themselves back into the tube)
    Predator sounds Broadcast a recording of birds of prey cries during 10 min
    Cycle disturbances Change of the light/dark cycle (e.g., complete reversal of the light/dark cycle, division of the light/dark cycle into four periods of 6 hr, or one to several illumination periods from 30 min to 2 hr during the dark phase and vice versa)

Basic Protocol 2: Assessment of Self‐Directed Activity and Anhedonia in Mice

  Materials
  • Four experimental groups of mice from the previous subdivisions in protocol 1 (non‐UCMS/vehicle, non‐UCMS/antidepressant, UCMS/vehicle, UCMS/antidepressant; sixteen mice per group)
  • Shortbread cookies [e.g., Pepito (LU) buttery shortbread cookies topped with chocolate, or Oreo (Kraft Foods)] cookies with two chocolate wafers separated by cream filling; the cookie must be appetent for mice in being somewhat crispy and sweet
  • 70% alcohol
  • 10% sucrose solution (elaborated with white sugar sold in conventional retail stores)
  • Device containing three aligned chambers (20‐cm length × 20‐cm width × 20‐cm height); only the colors of the walls and the floor are different between the chambers: white for the first one, gray for the second, and black for the third. The three chambers are linked by two gates with a door controlled by the experimenter (Fig. )
  • Light dimmer and luxmeter
  • Stopwatches
  • 32 individual cages for non‐UCMS mice (for the nest building test and the splash test)
  • Cotton nestlets (5 × 5 cm, 2 to 3 g; e.g., SERLAB, D0009 or LBS Biotech Nestlets)
  • One cage for the splash test
  • 1‐liter sprayer (e.g., garden hand sprayer) for the splash test
  • Lamp with red bulb
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Figures

Videos

Literature Cited

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Internet Resources
  http://www.affective.disorders.sciences.univ‐tours.fr
  Our laboratory Web site providing pictures and videos of the cookie test, the nest building test, and the splash test.
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