Post-Traumatic Stress Disorder Model

Model Introduction

Post-Traumatic Stress Disorder (PTSD) refers to a class of stress-related disorders that occur after an individual experiences severe psychological trauma. It can lead to psychological vulnerability and, in severe cases, significantly affect social functioning and quality of life.

PTSD was first included in the 3rd edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-3) in 1980. In the DSM-5 revised in 2013, PTSD was separately categorized under “Trauma- and Stressor-Related Disorders,” explicitly defining four typical behavioral characteristics:

1. Re-experiencing: Recurrent, involuntary, and intrusive distressing memories of the traumatic event, often manifesting as nightmares and flashbacks;
2. Avoidance: Avoiding memories, thoughts, or situations associated with the trauma;
3. Negative alterations in cognition and mood: Such as anhedonia and negative cognitions about oneself or the world;
4. Hyperarousal and Hypervigilance: Including aggressive behavior, reckless or self-destructive behavior, exaggerated startle response, and sleep disturbances.

Compared to DSM-4, the 5th edition expanded the scope of trauma exposure and emphasized the importance of negative cognitive and emotional changes.

Animal models are critical preliminary steps for assessing the safety and efficacy of new therapeutic strategies. They are used to identify potential therapeutic targets for behavioral and physiological abnormalities caused by psychological trauma and provide an experimental basis for resolving the neuromolecular mechanisms of PTSD. Currently, traumatic events are commonly simulated through prolonged stress, electric shocks, or predator odors, although no “perfect” animal model exists that fully meets all clinical criteria.

Research Applications

PTSD animal models can be used to simulate core behavioral changes following trauma exposure, including abnormal fear memory, anxiety-like behavior, avoidance behavior, and cognitive impairment. These models are utilized to:

• Evaluate the safety and efficacy of novel intervention strategies;
• Study abnormalities in the Hypothalamic-Pituitary-Adrenal (HPA) axis;
• Analyze functional changes in key brain regions such as the hippocampus and amygdala;
• Explore changes in inflammatory responses and related molecular signaling pathways.

Furthermore, different models show differences in the temporal dimension of behavioral changes, which can be used to study the evolution of PTSD-like symptoms after acute vs. chronic stress.

Key Points of Experimental Design

Rodents are primarily selected as experimental animals. Common models include:

1. Foot-Shock Model (FS) FS is a complex stressor that simultaneously affects physical and emotional states.
   • An electric shock of 1.5 mA for 2 seconds can induce conditioned fear memory and impact the social behavior of male B6N mice for up to 28 days.
   • This model exhibits symptoms such as persistent fear response, emotional apathy, social avoidance, hyperarousal, sleep disorders, cognitive impairment, and hypocortisolism, demonstrating good surface validity.
2. Single Prolonged Stress Model (SPS) First proposed by Liberzon et al., this model is used to simulate HPA axis abnormalities in PTSD.
   • The modeling process includes:
     • 2 hours of restraint stress;
     • Immediately followed by 20 minutes of forced swimming;
     • 15 minutes of rest;
     • Exposure to ether vapor until loss of consciousness;
     • Subsequently, at least 7 days of non-interference.
   • This model leads to impaired fear memory extinction, manifesting as persistent fear, anxiety, and avoidance. Studies show significant depression-like behavior on days 1 and 7, and persistent anxiety-like behavior after 2 weeks, suggesting time-dependent behavioral changes.
3. Underwater Trauma Model (UWT) Proposed by Richter-Levin in 1996.
   • The modeling method involves placing rats in a water maze with the platform removed to swim for 1 minute, followed by restricted movement to simulate a “near-drowning” traumatic event.
   • This model leads to:
     • Elevated anxiety levels persisting for 1 month;
     • Spatial memory impairment for 3 weeks upon re-exposure to the traumatic environment;
     • No difference in spatial memory capacity compared to the control group in non-traumatic environments.
   • This model is closely related to brain regions such as the hippocampus, amygdala, and dentate gyrus. Research found that UWT causes long-term overexpression of pro-inflammatory cyclooxygenase-2 (COX-2) in the hippocampal CA1 region, impairs long-term potentiation (LTP) in the dentate gyrus, and affects ERK-2 activity in the ventral hippocampus and basolateral amygdala.

Key Detection Indicators

Behavioral Indicators:

• Conditioned fear memory
• Fear memory extinction capacity
• Anxiety-like behavior
• Depression-like behavior
• Social avoidance
• Spatial memory capacity
• Sleep disturbances

Neurobiological Indicators:

• HPA axis dysfunction
• COX-2 expression in hippocampal CA1
• LTP changes in the dentate gyrus
• ERK-2 activity in the ventral hippocampus and basolateral amygdala

Model Limitations:

• Pathogenesis of PTSD is not yet fully elucidated
• Lack of unified evaluation standards
• Difficulty in differentiating subtypes and comorbid psychiatric disorders
• Lack of consensus on the translation between animal models and clinical scale diagnoses