Age‑Dependent CRF‑Mediated Suppression of Intercalated Cell GABAergic Tone Underlies the Decoupling of Amygdala Hyperreactivity from Trait Anxiety in Aging

Aging is associated with paradoxical amygdala hyperreactivity during cognitive tasks despite lower trait anxiety, suggesting a compensatory mechanism that masks subjective distress[1]. We hypothesize that this compensation relies on heightened GABAergic output from intercalated amygdala cells (ITCs) that inhibit basolateral amygdala output. In young adults, ITC recruitment scales with threat level and supports extinction learning[3]. With age, baseline ITC tone increases to offset amplified basolateral excitation, preserving low anxiety scores. However, stress‑induced corticotropin‑releasing factor (CRF) release in the central amygdala enhances locus coeruleus‑noradrenergic (LC‑NE) signaling, which suppresses ITC GABA release via α2‑adrenergic autoreceptors on ITC terminals. This CRF‑LC‑NE–mediated disinhibition of basolateral circuits unmasks the underlying hyperreactivity, decoupling neural activation from subjective experience and producing extinction deficits when extinction follows conditioning shortly after stress[2].

Testable predictions: (1) In aged rodents, chemogenetic activation of ITCs during a working‑memory task will reduce amygdala calcium signals without altering performance, whereas ITC inhibition will increase amygdala activity and raise anxiety‑like behavior in the elevated plus maze. (2) Systemic CRF‑R1 antagonism in aged animals will restore ITC‑mediated inhibition, normalizing amygdala‑prefrontal coherence during extinction recall and improving retention of fear extinction. (3) Optogenetic stimulation of LC‑NE terminals in the central amygdala of aged mice will reproduce the extinction deficit seen in young stressed animals, an effect blocked by local GABA_A agonist infusion into ITC clusters. (4) Single‑cell RNA‑seq of sorted ITCs from aged versus young mice will reveal age‑upregulated GABA synthesis genes (Gad1, Gad2) and down‑regulated α2‑adrenergic receptor (Adra2a) expression, with CRF exposure reversing this pattern.

Falsifiable outcomes: If ITC manipulation fails to modulate amygdala activation or anxiety measures in aged subjects, or if CRF‑R1 blockade does not rescue extinction despite intact ITC activity, the hypothesis would be refuted. Conversely, confirming that boosting ITC GABAergic tone mitigates amygdala hyperreactivity and that CRF‑LC‑NE signaling gates this control would mechanistically explain why older adults show preserved neural reactivity yet low trait anxiety, and why a subset develops late‑life anxiety disorders when stress overwhelms this compensatory brake.