Developing of Focal Ischemia in the Hippocampus or the Amygdala Reveals a Regional Compensation Rule for Fear Memory Acquisition

Abstract

Circuit compensation is often observed in patients with acute ischemic stroke, suggesting the importance of the interaction between brain regions. Also, contextual fear memory is an association between multisensory contexts and fearful stimuli, for which the interaction between the hippocampus and the amygdala is believed to be critical. To understand how focal ischemia in one region could influence the other region, we used a modified photo-thrombosis to induce focal ischemia in the hippocampus or the amygdala or both in freely-moving rats. We found that the learning curve and short-term memory (STM) were not affected in the rats although focal ischemia was induced 5 h before learning in either the hippocampus or the amygdala; these were impaired by the induction of ischemia in both the regions. Furthermore, the learning curve and STM were impaired when ischemia was induced 24 h before learning in either the hippocampus or the amygdala when the synaptic transmission was altered in one region because of ischemia in the other region. These results suggest that the circuit compensation between the hippocampus and the amygdala is critical for fear memory acquisition.

Sleep, NMDA Receptor Subunits, and the Compensatory Pathway: Understanding Contextual Fear Conditioning in the Absence of the Dorsal Hippocampus

“…Additional training trials can gradually develop contextual fear within these alternative circuits, indicating their remarkable adaptive potential (Coelho et al ., 2018; Cowansage et al ., 2014; Kant and Jha, 2019a, 2023; M. S. Fanselow, 2010; Poulos et al ., 2010; Yu et al ., 2021; Zelikowsky et al ., 2013). In the absence of the DH, the micro-circuitries of the medial prefrontal cortex (mPFC), particularly the infralimbic (IL) and prelimbic (PL) cortices, facilitate contextual fear conditioning (Zelikowsky et al ., 2013).…”