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Summary

Abstract

Introduction

Protocol

Representative Results

Discussion

Acknowledgements

Materials

References

Behavior

Stress-Enhanced Fear Learning, a Robust Rodent Model of Post-Traumatic Stress Disorder

Published: October 13th, 2018

DOI:

10.3791/58306

1Department of Psychology, University of California, Los Angeles, 2Staglin Center for Brain and Behavioral Health, University of California, Los Angeles, 3Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles

Here we describe the detailed methodology required to conduct stress-enhanced fear learning (SEFL) experiments, a preclinical model of post-traumatic stress disorder, in both rats and mice. The model utilizes aspects of Pavlovian fear conditioning and freezing as an index of enhanced fear in rodents.

Fear behaviors are important for survival, but disproportionately high levels of fear can increase the vulnerability for developing psychiatric disorders such as post-traumatic stress disorder (PTSD). To understand the biological mechanisms of fear dysregulation in PTSD, it is important to start with a valid animal model of the disorder. This protocol describes the methodology required to conduct stress-enhanced fear learning (SEFL) experiments, a preclinical model of PTSD, in both rats and mice. SEFL was developed to recapitulate critical aspects of PTSD, including long-term sensitization of fear learning caused by an acute stressor. SEFL uses aspects of Pavlovian fear conditioning but produces a distinct and robust sensitized fear response far greater than normal conditional fear responses. The trauma procedure involves placing a rodent in a conditioning chamber and administering 15 unsignaled shocks randomly distributed over 90 minutes (for rat experiments; for mouse experiments, 10 unsignaled shocks randomly distributed over 60 minutes are used). On day 2, rodents are placed in a novel conditioning context where they receive a single shock; then, on day 3 they are placed back in the same context as on day 2 and tested for changes in freezing levels. Rodents that previously received the trauma display enhanced levels of freezing on the test day compared to those that received no shocks on the first day. Thus, with this model, a single highly stressful experience (the trauma) produces extreme fear of the stimuli associated with the traumatic event.

Fear is a critical behavior for survival, enabling individuals to recognize and respond to threats. However, exaggerated fear responses can contribute to the development of psychiatric disorders such as post-traumatic stress disorder (PTSD). One characteristic of PTSD is an exaggerated response to mild stressors, particularly those reminiscent of the original trauma, and a tendency to develop new fears1,2. In the laboratory, fear is often measured through freezing behavior, which is a reliable and ethologically valid index of fear in humans and rodents3,4

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1. Subjects

  1. Rats
    1. Order rats to arrive when they are approximately 90 days old and single-housed in standard rat cages.
      Note: Single housing is advised, as group housing produces variability due to interactions between animals in the home cage, particularly following stress exposure. SEFL has been demonstrated in male and female rats, in Long-Evans and Sprague Dawley rats, and in rats as young as 19 days old7,10.
    2. Randomly.......

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Results of the trauma context test on Day 2 are shown in Figure 1. Animals in the trauma condition showed significantly higher levels of freezing in Context A compared to the no trauma controls, indicating acquisition of fear to the trauma context [rats: F(1,17) = 23.58, p < 0.01; mice: F(1,14) = 666.50, p < 0.0001]. Freezing during the baseline period before the single shock in the novel context on Day 3 is shown in

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SEFL is a robust behavioral model of PTSD that can be recapitulated in both rats and mice and can be used to study the sensitized fear responses that characterize PTSD. Following traumatic stress, rodents show an increased fear response in a distinctly different context only after that context is paired with a mild stressor that serves as a reminder of a previous traumatic experience. Following the traumatic stress rodents unsurprisingly show high levels of fear when returned to the traumatic stress context on Day 2, ind.......

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This work was funded by National Institute of Health R01AA026530 (MSF), Staglin Center for Brain and Behavioral Health (MSF), NRSA-F32 MH10721201A1 and NARSAD 26612 (AKR), and NSF DGE-1650604 (SG).

....

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Name Company Catalog Number Comments
Fear Conditioning Chamber for Low Profile Floors Med Associates Inc. VFC-008-LP Fear conditioning chamber
Sound Attenuating Cubicle Med Associates Inc. NIR-022SD Sound-attentuaing cubicle to prevent intrusion of outside noise
NIR/White Light Control Box Med Associates Inc. NIR-100VR Light control box capable of delivering white and near-infrared light
NIR VFC Light Box Med Associates Inc. NIR-100L2 White overhead houselight
Windex Original Glass Cleaner Windex Solution for cleaning and scenting fear conditioning chambers between animals
Acetic acid Fisher Scientific A38-212 Solution for cleaning and scenting fear conditioning chambers between animals
A-Frame Chamber Insert Med Associates Inc. ENV-008-IRT Black Plexiglas triangular insert to differentiate internal layout of Contexts A and B
Curved Wall Insert Med Associates Inc. VFC-008-CWI White plastic sheet to differentiate internal layout of Contexts A and B
Low Profile Contextual Grid Floor with 1/8" Grid Rods for Mouse Med Associates Inc. VFC-005A Flat grid floor for mice
Low Profile Contextual Grid Floor with Alternating 1/8" & 3/16" Grid Rods Mouse Med Associates Inc. VFC-005-S Staggered grid floor for mice
Low Profile Contextual Grid Floor with 1/8" Staggered Grid Rods for Mouse Med Associates Inc. VFC-005A-L Alternating grid floor for mice
Low Profile Contextual Grid Floor with 3/16" Grid Rods for Rat Med Associates Inc. VFC-005 Flat grid floor for rats
Low Profile Contextual Grid Floor with Alternating 3/16" & 3/8" Grid Rods Med Associates Inc. VFC-005-L Alternating grid floor for rats
Low Profile Contextual Grid Floor with 3/16" Staggered Grid Rods for Rat Med Associates Inc. VFC-005-S Staggered grid floor for rats
Metal pans Med Associates Inc. Metal pans to catch droppings underneath grid floors
Standalone Aversive Stimulator/Scrambler Med Associates Inc. ENV-414S Shock generator and scrambler for footshock delivery
Multimeter Fluke 87-5 Tool for measuring footshock amplitude
VideoFreeze Software Med Associates Inc. SOF-843 VideoFreeze software for controlling shock delivery
High Speed Firewire Monochrome Video Camera Med Associates Inc. VID-CAM-MONO-4 Video camera capable of recording in near-infrared light

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