Neurocircuitry of fear extinction in adult and juvenile rats

• Published in: Behavioural brain research 2018-10, Vol.351, p.161-167
• Main Authors: Ganella, Despina E., Nguyen, Ly Dao, Lee-Kardashyan, Liubov, Kim, Leah E., Paolini, Antonio G., Kim, Jee Hyun
• Format: Article
• Language: English
• Subjects: Amygdala; Animals; Brain - cytology; Brain - growth & development; Circuitry; Conditioning (Psychology) - physiology; Development; Extinction; Extinction, Psychological - physiology; Fear - physiology; Freezing Reaction, Cataleptic; Hippocampus; Male; Neural Pathways - cytology; Neural Pathways - growth & development; Neuroanatomical Tract-Tracing Techniques; Neurons - cytology; Neurons - physiology; Prefrontal cortex; Proto-Oncogene Proteins c-fos - metabolism; Rats, Sprague-Dawley
• ISSN: 0166-4328; 1872-7549
• DOI: 10.1016/j.bbr.2018.06.001

•Juveniles and adults have comparable BLA projections to hippocampus.•Juveniles and adults have comparable BLA projections to infralimbic cortex.•Adults show activated BLA cells projecting to hippocampus after extinction.•Juveniles do not show activated BLA to hippocampus cells.•Activated BLA projections correlate with behavior in adults but not in juveniles. In contrast to adult rodents, juvenile rodents fail to show relapse following extinction of conditioned fear. Using different retrograde tracers injected into the infralimbic cortex (IL) and the ventral hippocampus (vHPC) in conjunction with c-Fos and parvalbumin (PV) immunochemistry, we investigated the neurocircuitry of extinction in juvenile and adult rats. Regardless of fear extinction or retrieval, juvenile rats had more c-Fos+ neurons in the basolateral amygdala (BLA) compared to adults, and showed a higher proportion of c-Fos+ IL-projecting neurons. Adult rats had more activated vHPC-projecting BLA neurons following extinction compared to retrieval, a difference not observed in juvenile rats. The number of activated vHPC- or IL-projecting BLA neurons was significantly correlated with freezing levels in adult, but not juvenile, rats. We also identified activated neurons in the BLA that simultaneously project to the IL and vHPC in the retrieval groups at both ages. This study provides novel insight into the neural process underlying extinction, especially in the juvenile period.