A Protocol for the Induction of Posttraumatic Stress-Disorder (PTSD)-like Behavior in Mice

Summary

In this study, post-traumatic stress disorder (PTSD)-like behavior is induced in mice using two sessions of inescapable electric foot shock. PTSD-like and resilient animals are identified using several assays for PTSD-specific behaviors.

Abstract

Post-traumatic stress disorder (PTSD) is a debilitating psychiatric condition that precipitates in ~10% of individuals exposed to a traumatic event (TE). Symptoms include recurrent and intrusive thoughts, sleep disturbance, hypervigilance, exaggerated startle, and reckless or destructive behavior. Given the complex and heterogeneous nature of the disease, animal models for PTSD-like symptomatology are of increasing interest to the field of PTSD research. Because resilience to PTSD-like symptomatology is an important epidemiologic aspect of PTSD, animal models that resolve vulnerable and resilient animals are of particular value. Due to the complex nature of the PTSD phenotype and the potential overlaps between PTSD-like behavior and behaviors associated with other stress-induced psychopathologies such as anxiety or depression, animal models that utilize multiple readouts for PTSD-like behavior are also of increasing value. We utilize a paradigm developed by Lebow et al. 2012 for the induction and identification of PTSD-like symptomatology in mice. This paradigm utilizes inescapable electric foot shock, administered in two decontextualized sessions over two consecutive days. Stressed mice perform four behavioral tests - dark/light transfer, marble burying, acoustic startle, and home cage activity - to generate five behavioral readouts of PTSD-like behavior: % risk assessment (%RA), % marbles buried (%MB), % prepulse inhibition (%PPI), latency to peak startle amplitude (LPSA), and % light phase activity (%LPA). PTSD-like symptomatology is characterized by decreased %RA, increased %MB, decreased %PPI, decreased LPSA, and increased %LPA. The 20% of animals displaying the most PTSD-like behavior in each test are awarded a certain number of points depending on the test, and animals scoring sufficient points are designated as PTSD-like, while animals scoring no points are designated PTSD-resilient. This paradigm identifies PTSD-like behavior in ~15% of animals, a rate comparable to that observed in humans. This protocol represents a robust and reproducible paradigm for the induction of PTSD-like behavior in mice.

Introduction

Post-traumatic stress disorder (PTSD) is debilitating psychopathology that can precipitate in individuals who have been exposed to a traumatic event (TE)¹. According to the DSM-V, TE exposure may take many forms, including direct or repeated indirect exposure to a real or perceived threat of death, bodily harm, or sexual violence to oneself or to another². PTSD symptomatology is characterized by intrusive negative thoughts and recollections, hyperarousal, hypervigilance, increased risk-taking behavior, and disrupted sleep cycles³. Lifetime prevalence of TE exposure worldwide is relatively high at ....

Protocol

All procedures described here are approved by the Mayo Clinic Institutional Animal Care and Use Committee (IACUC).

1. Animals and housing

1. House 10-week-old male C57BL/6J mice 4-to-a-cage in standard housing conditions (standard microisolator cage, 70 °F room temperature (RT), food and water ad libitum, 12 h/12 h light/dark cycle).

2. PTSD-induction

1. Trauma session
   1. Prepare the fear conditioning equipment and chamber.
      1. Program the trauma protocol in the fear conditioning software. Set a total time to 5100 s (85 mi....

Results

We expect to see animals displaying PTSD-like behavior in each behavioral test evenly distributed across all cohorts. A concentration of PTSD-like animals in any one cohort may indicate artifacts introduced either during the PTSD induction or behavioral testing. Animals scoring points in each behavioral readout are equally distributed across all cohorts tested (Figure 2). 7 of the 48 animals (14.6%) exposed to the PTSD-induction paradigm scored 5 or more points and were designated PTSD-like .......

Discussion

PTSD is a complex and heterogenous psychiatric disease. Unfortunately, there is currently no reliable animal model for PTSD-like behavior, and behavioral paradigms for the induction of PTSD-like behavior are the most reliable means of generating animals displaying a PTSD-like behavioral phenotype. The paradigm described here provides a robust and reliable means of precipitating a PTSD-like behavioral phenotype due to the use of acute trauma to precipitate PTSD-like behavior and multiple PTSD-specific behavioral readouts .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetic acid, glacial	Sigma Aldrich	AX0073
Benchtop Balance	Fisher Scientific	01-913-925
Clocklab Data Collection Suite	Actimetrics	-	Home cage activity cages
Deciblemeter
Ethovision XT14 Software	Noldus	-	Movement tracking software
Ethyl alcohol	Sigma Aldrich	443611
Light/Dark Box	Noldus	-	Light/dark transfer box
Lux Meter
Monochrome GigE Camera	Noldus	-	Requires Ceiling Mounting Hardware Available from Noldus
NIR Video Fear Conditioning Package for Mouse [Standard, USB]	Med Associates	MED-VFC2-USB-M	Fear conditioning equipment and chamber. Package includes all equipment needed to assay 1 animal at a time.
Spray Bottle	Thermo Scientific	BirA500
SR LAB Software	San Diego Instruments	-	Startle response software
SR LAB Startle Response Unit	San Diego Instruments	-	Acoustic startle unit
Video Fear Coniditioning "Video Freeze " Software	Med Associates	SOF-843	Fear conditioning software
White noise machine	Med Associates	ENV-230