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 approximately 64%-70%3, though lifetime prevalence of PTSD remains comparatively low, at ~1.3%-12%4. This disparity in the prevalence of TE exposure relative to PTSD precipitation suggests a strong gene x environment interaction in vulnerability to PTSD. Given the current absence of a reliable vertebrate model of PTSD-like behavior, the field relies on behavioral paradigms for the induction of PTSD-like symptomatology5.
PTSD is a complex and highly heterogeneous psychiatric disorder, and developing a robust and reliable animal model for PTSD-like symptomatology has been challenging. Commonly used readouts for PTSD-like behavior, such as freezing, are also symptomatic of other trauma-induced psychopathologies, namely, anxiety, and depression6. This is further complicated by the high comorbidity between PTSD and depression2. Recent investigations have shown that rats that have witnessed traumatic events display increased anxiety and depression behaviors7,8,9, further demonstrating the importance of assessing PTSD-specific behaviors when utilizing behavioral models of PTSD in rodents. Additionally, resilience to PTSD-like symptomatology following traumatic event exposure is a significant epidemiologic feature of PTSD, as lifetime incidence of traumatic event exposure worldwide far outstrips lifetime prevalence of PTSD. Historically, behavioral models for induction of PTSD-like behavior, such as those investigating fear memory10,11, did not resolve PTSD-like animals from trauma-exposed controls (PTSD-resilient animals), treating all trauma-exposed animals as PTSD-like, and commonly used few behavior readouts, such as freezing, that are either not specifically symptomatic of PTSD or are symptomatic of other trauma-induced psychopathologies such as anxiety or depression12. While these paradigms are effective in investigating neural circuits of fear memory, the lack of a robust and specific assessment of PTSD-like behavior may impact the translation of these data. The current state of the field, therefore, focuses on paradigms utilizing multiple PTSD-specific behavioral readouts to identify both PTSD-like and resilient animals12.
We utilize a recently developed paradigm for the induction of PTSD-like behavior in mice which identifies both PTSD-like and resilient animals using a series of four behavioral tests to assay five PTSD-like behavioral readouts13,14. PTSD-like behavior is induced using decontextualized electric foot shock across two sessions. Animals are first exposed to a severe Trauma session on the first day, followed by a relatively mild Trigger session the following day (Figure 1). This combination has been shown to significantly increase the precipitation of PTSD-like behavior. This paradigm utilizes an acute stress model for PTSD induction rather than chronic stress (which may induce a more depressive phenotype15) or traumatic brain injury (which may result in a distinct PTSD-like phenotype14). Similarly, the behavioral readouts utilized to identify PTSD-like behavior in this paradigm – reduced risk-taking behavior, increased marble burying, reduced prepulse inhibition, reduced latency to peak startle amplitude, and increased light phase activity (Figure 1) – are specific to PTSD-like behavior, rather than to other trauma-induced psychopathologies such as anxiety or depression. Additionally, the use of multiple behavioral readouts, and the need for animals to display multiple PTSD-like behaviors in order to be designated PTSD-like, increases the likelihood that animals designated PTSD-like are truly displaying a PTSD-like phenotype. Together, these features of the protocol ensure that this paradigm is a robust and reliable means for inducing PTSD-like symptomatology in mice.
Protocol
Representative Results
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 …
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was made possible by the generosity of the Hayward Foundation and Marriot Family. We would also like to acknowledge the hard work and expertise of the Tulane University and Mayo Clinic IACUC committees and Departments of Comparative Medicine, as well as the Mayo Clinic Rodent Behavioral Research Facility.
Materials
| 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 |
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