Role of Amygdala-Infralimbic Cortex Circuitry in Glucocorticoid-induced Facilitation of Auditory Fear Memory Extinction

Targeting Human Glucocorticoid Receptors in Fear Learning: A Multiscale Integrated Approach to Study Functional Connectivity

Fear extinction is a phenomenon that involves a gradual reduction in conditioned fear responses through repeated exposure to fear-inducing cues. Functional brain connectivity assessments, such as functional magnetic resonance imaging (fMRI), provide valuable insights into how brain regions communicate during these processes. Stress, a ubiquitous aspect of life, influences fear learning and extinction by changing the activity of the amygdala, prefrontal cortex, and hippocampus, leading to enhanced fear responses and/or impaired extinction. Glucocorticoid receptors (GRs) are key to the stress response and show a dual function in fear regulation: while they enhance the consolidation of fear memories, they also facilitate extinction. Accordingly, GR dysregulation is associated with anxiety and mood disorders. Recent advancements in cognitive neuroscience underscore the need for a comprehensive understanding that integrates perspectives from the molecular, cellular, and systems levels. In particular, neuropharmacology provides valuable insights into neurotransmitter and receptor systems, aiding the investigation of mechanisms underlying fear regulation and potential therapeutic targets. A notable player in this context is cortisol, a key stress hormone, which significantly influences both fear memory reconsolidation and extinction processes. Gaining a thorough understanding of these intricate interactions has implications in terms of addressing psychiatric disorders related to stress. This review sheds light on the complex interactions between cognitive processes, emotions, and their neural bases. In this endeavor, our aim is to reshape the comprehension of fear, stress, and their implications for emotional well-being, ultimately aiding in the development of therapeutic interventions.

Update on neurobiological mechanisms of fear: illuminating the direction of mechanism exploration and treatment development of trauma and fear-related disorders

Fear refers to an adaptive response in the face of danger, and the formed fear memory acts as a warning when the individual faces a dangerous situation again, which is of great significance to the survival of humans and animals. Excessive fear response caused by abnormal fear memory can lead to neuropsychiatric disorders. Fear memory has been studied for a long time, which is of a certain guiding effect on the treatment of fear-related disorders. With continuous technological innovations, the study of fear has gradually shifted from the level of brain regions to deeper neural (micro) circuits between brain regions and even within single brain regions, as well as molecular mechanisms. This article briefly outlines the basic knowledge of fear memory and reviews the neurobiological mechanisms of fear extinction and relapse, which aims to provide new insights for future basic research on fear emotions and new ideas for treating trauma and fear-related disorders.

Glucocorticoid- β-adrenoceptors interactions in the infralimbic cortex in acquisition and consolidation of auditory fear memory extinction in rats

This study investigated the interactive effect of glucocorticoid and β-adrenoceptors in the infralimbic (IL) cortex on the acquisition and consolidation of fear extinction in rats' auditory fear conditioning (AFC) task. On day 1, rats underwent habituation for 9 min (12 tonnes, 10 s, 4 kHz, 80 dB, without footshock). On day 2 (conditioning), rats received 3 mild electrical footshocks (US; 2 s, 0.5 mA) paired with the auditory-conditioned stimulus (CS; tone: 30 s, 4 kHz, 80 dB). On days 3-5 (Ext 1-3), rats received 15 tonnes with no footshock in the test box. Intra-IL injection of corticosterone (CORT, 20 ng/0.5 μl per side) before Ext 1 and after Ext 1-2, respectively, facilitated the acquisition and consolidation of fear memory extinction. Intra-IL injection of the β₂-adrenoceptor agonist clenbuterol (CLEN, 50 ng/0.5 μl per side) inhibited, but the β-adrenoceptor antagonist propranolol (PROP, 500 ng/0.5 μl per side) enhanced the facilitatory effects of CORT on fear memory extinction. CORT injection before the acquisition of fear extinction increased p-ERK levels in the IL. Co-injection of CORT with CLEN increased, but PROP decreased p-ERK activities. CORT injection after the consolidation of fear extinction increased p-CREB in the IL. Co-injection of CORT with CLEN increased, but PROP reduced p-CREB activities. Our findings show that corticosterone facilitates the acquisition and consolidation of fear memory extinction. GRs and β-adrenoceptors in the IL jointly regulate fear memory extinction via ERK and CREB signaling pathways. This pre-clinical animal study may highlight the effect of GRs and β-adrenoceptors of the IL cortex in regulating fear memory processes in fear-related disorders such as PTSD.