Chronic activation of fear engrams induces extinction‐like behavior in ethanol‐exposed mice

• Published in: Hippocampus 2021-01, Vol.31 (1), p.3-10
• Main Authors: Cincotta, Christine, Murawski, Nathen J., Grella, Stephanie L., McKissick, Olivia, Doucette, Emily, Ramirez, Steve
• Format: Article
• Language: English
• Subjects: addiction; Alcohol; Cell activation; engram; Ethanol; extinction; Extinction behavior; Fear conditioning; hippocampus; Neural networks; optogenetics; withdrawal
• ISSN: 1050-9631; 1098-1063
• DOI: 10.1002/hipo.23263

Alcohol withdrawal directly impacts the brain's stress and memory systems, which may underlie individual susceptibility to persistent drug and alcohol‐seeking behaviors. Numerous studies demonstrate that forced alcohol abstinence, which may lead to withdrawal, can impair fear‐related memory processes in rodents such as extinction learning; however, the underlying neural circuits mediating these impairments remain elusive. Here, we tested an optogenetic strategy aimed at mitigating fear extinction retrieval impairments in male c57BL/6 mice following exposure to alcohol (i.e., ethanol) and forced abstinence. In the first experiment, extensive behavioral extinction training in a fear‐conditioned context was impaired in ethanol‐exposed mice compared to controls. In the second experiment, neuronal ensembles processing a contextual fear memory in the dorsal hippocampus were tagged and optogenetically reactivated repeatedly in a distinct context in ethanol‐exposed and control mice. Chronic activation of these cells resulted in a context‐specific, extinction‐like reduction in fear responses in both control and ethanol‐exposed mice. These findings suggest that while ethanol can impair the retrieval an extinction memory, optogenetic manipulation of a fear engram is sufficient to induce an extinction‐like reduction in fear responses.