Hypothesis

Chronic CRF neuron hyperactivity in the basolateral amygdala shifts proteostasis from soluble turnover to adaptive amyloid‑like aggregation, which initially sequesters misfolded proteins but later becomes pathological and disrupts fear extinction circuits.

Mechanistic Reasoning

• Persistent CRF signaling raises intracellular Ca²⁺ and activates cAMP/PKA pathways, increasing protein synthesis and mitochondrial ROS production. Elevated oxidative stress damages nascent polypeptides, overwhelming chaperone capacity.
• When chaperones and the ubiquitin‑proteasome system saturate, the cell redirects misfolded proteins into β‑sheet‑rich assemblies. These inclusions are thioflavin‑S positive, ubiquitinated, and co‑localize with p62, reflecting an adaptive sequestration strategy akin to that described for stress‑induced granules.
• In young animals this aggregation limits soluble toxic species, preserving vmPFC‑BLA synaptic plasticity needed for extinction learning. With age, cumulative CRF drive pushes the aggregation threshold, forming larger, less dynamic aggregates that impair vesicle release and receptor trafficking at excitatory synapses.
• Consequently, vmPFC‑driven inhibition of BLA output weakens, zif268 remains high after extinction training, and freezing persists Aged rats fail to reduce freezing behavior during extinction and show persistent zif268 expression in the basolateral amygdala; Middle-aged and older rats exhibit dissociation between extinction performance and BLA synaptic function; Lifelong CRF overproduction reduces functional GABA_A and mGluR receptor sensitivity in the amygdala, decreasing inhibition and heightening stress responsivity; Early-life stress induces lasting hyperexcitability in central amygdala CRF neurons; vmPFC inputs to the amygdala are critical for extinction formation

Testable Predictions

1. Aged rats exhibiting CRF overproduction will show increased thioflavin‑S‑positive aggregates in the basolateral amygdala that correlate with heightened zif268 expression after extinction trials.
2. Pharmacological blockade of CRF₁ receptors in middle‑aged animals will reduce aggregate load, restore GABA_A and mGluR sensitivity, and rescue extinction performance without affecting baseline anxiety.
3. Enhancing autophagy via spermidine treatment will clear amyloid‑like inclusions in the BLA and improve extinction retention, whereas inhibiting autophagy with chloroquine will exacerbate aggregate accumulation and extinction deficits even in young rats with acute CRF elevation.
4. Introducing a peptide that blocks amyloid‑like aggregation (e.g., a β‑sheet breaker) in aged rats will paradoxically increase soluble phosphorylated tau and worsen extinction, supporting the protective role of early aggregation.
5. Viral‑mediated knock‑down of the aggregation‑prone protein (e.g., Hsp70 client) specifically in CRF neurons will diminish aggregate formation and normalize vmPFC‑BLA circuit function during extinction recall.