Dysregulated Extinction Engram Reactivation in the Infralimbic Cortex in Comorbid PTSD/AUD
Abstract
Background: Comorbid alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) impair extinction learning and memory, critical for recovering from conditioned fear responses. Despite its prevalence, the neurobiological mechanisms remain poorly understood. This study examines how prior stress and alcohol exposure alter fear extinction learning and long-term memory, focusing on neuronal activity and engram reactivation in the infralimbic cortex (IfL). Methods: Experiment 1: Adult male Wistar rats were assigned to Stress & Alcohol (RS+CIE), Control (No-Stress+Air), or Home Cage (HC) groups. RS+CIE rats underwent restraint stress and chronic intermittent ethanol (CIE) vapor exposure, modeling trauma and alcohol dependence. After withdrawal, RS+CIE and Control rats underwent Contextual Fear Conditioning (CFC) to assess stress sensitivity by examining the acquisition of a conditioned fear response and extinction of fear behaviors. In vivo single-unit electrophysiological recorded IfL activity post-extinction. Experiment 2: Building on Experiment 1, which showed decreased IfL activity in RS+CIE rats post-extinction, we examined extinction engram formation/reactivation using a targeted recombination in active populations (TRAP)-based approach. Rats received bilateral IfL injections of inducible Cre recombinase (CreERT2) and Cre-dependent mCherry to label neurons activated during extinction. After the final extinction session, 4-hydroxytamoxifen (4-OHT) was administered to tag active neurons. Long-term extinction memory was assessed 5 weeks later during remote extinction recall, followed by confocal microscopy to quantify TRAP-labeled neurons (mCherry+) and colocalization with cFos. Results: Experiment 1, RS+CIE rats exhibited significantly reduced IfL activity post-extinction training (p=0.001). In Experiment 2, RS+CIE rats displayed increased freezing during remote extinction recall [t(30)=4.238,p=0.0006], impaired long-term memory, reduced mCherry+ neurons [F(1,4)=23,p=0.009], and decreased mCherry+/cFos+ colocalization [F(1,4)=10.78,p=0.03]. Conclusion: These findings provide novel insights into the cellular mechanisms underlying extinction memory deficits in PTSD/AUD. By demonstrating impaired reactivation of extinction engrams in the IfL, our findings shed light on the potential neural basis of relapse vulnerability in this population.
Start Time
16-4-2025 2:30 PM
End Time
16-4-2025 3:30 PM
Room Number
311
Presentation Type
Oral Presentation
Presentation Subtype
Grad/Comp Orals
Presentation Category
Health
Faculty Mentor
Justin Gass
Dysregulated Extinction Engram Reactivation in the Infralimbic Cortex in Comorbid PTSD/AUD
311
Background: Comorbid alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) impair extinction learning and memory, critical for recovering from conditioned fear responses. Despite its prevalence, the neurobiological mechanisms remain poorly understood. This study examines how prior stress and alcohol exposure alter fear extinction learning and long-term memory, focusing on neuronal activity and engram reactivation in the infralimbic cortex (IfL). Methods: Experiment 1: Adult male Wistar rats were assigned to Stress & Alcohol (RS+CIE), Control (No-Stress+Air), or Home Cage (HC) groups. RS+CIE rats underwent restraint stress and chronic intermittent ethanol (CIE) vapor exposure, modeling trauma and alcohol dependence. After withdrawal, RS+CIE and Control rats underwent Contextual Fear Conditioning (CFC) to assess stress sensitivity by examining the acquisition of a conditioned fear response and extinction of fear behaviors. In vivo single-unit electrophysiological recorded IfL activity post-extinction. Experiment 2: Building on Experiment 1, which showed decreased IfL activity in RS+CIE rats post-extinction, we examined extinction engram formation/reactivation using a targeted recombination in active populations (TRAP)-based approach. Rats received bilateral IfL injections of inducible Cre recombinase (CreERT2) and Cre-dependent mCherry to label neurons activated during extinction. After the final extinction session, 4-hydroxytamoxifen (4-OHT) was administered to tag active neurons. Long-term extinction memory was assessed 5 weeks later during remote extinction recall, followed by confocal microscopy to quantify TRAP-labeled neurons (mCherry+) and colocalization with cFos. Results: Experiment 1, RS+CIE rats exhibited significantly reduced IfL activity post-extinction training (p=0.001). In Experiment 2, RS+CIE rats displayed increased freezing during remote extinction recall [t(30)=4.238,p=0.0006], impaired long-term memory, reduced mCherry+ neurons [F(1,4)=23,p=0.009], and decreased mCherry+/cFos+ colocalization [F(1,4)=10.78,p=0.03]. Conclusion: These findings provide novel insights into the cellular mechanisms underlying extinction memory deficits in PTSD/AUD. By demonstrating impaired reactivation of extinction engrams in the IfL, our findings shed light on the potential neural basis of relapse vulnerability in this population.
