Hypothesis: CREB-Dependent GABAergic Rewiring of Central Amygdala CRF Neurons Drives Age-Related Decoupling of Amygdala Activity and Anxiety

Core Idea With aging, central amygdala (CeA) CRF neurons show reduced CREB phosphorylation, which enhances GABAergic tonic inhibition from prelimbic prefrontal cortex (plPFC) inputs. This shift lowers CeA output to downstream fear circuits, weakening the positive link between amygdala activation and trait anxiety seen in young adults while promoting safety learning.

Mechanistic Steps

1. CREB downregulation in aged CeA CRF neurons decreases transcription of excitatory synapse genes (e.g., Grik4) and increases expression of GABA‑A receptor subunits, making these neurons less responsive to glutamatergic drive [2].
2. Increased plPFC‑CeA BDNF‑TrkB signaling (known to rise with healthy aging) activates phosphatases that dephosphorylate CREB, reinforcing the low‑CREB state [6].
3. Enhanced GABAergic tone reduces spontaneous firing and blunts CRF release, attenuating the orexin‑LC‑NE arousal axis that normally biases cortico‑amygdala circuits toward fear encoding [4][5].
4. Behavioral prediction: In aged mice, optogenetic plPFC‑CeA stimulation will produce stronger inhibition of CRF neuron firing and faster fear extinction than in young mice; conversely, viral overexpression of CREB in aged CeA CRF neurons will restore excitatory coupling, reinstate positive amygdala‑anxiety correlation, and impair extinction.

Testable Predictions

• Measure pCREB levels in CeA CRF neurons from young (3 mo) vs aged (18‑24 mo) mice during extinction recall; expect lower pCREB in aged group [2].
• Use fiber photometry to record GABA sensor signals in CeA during plPFC stimulation; aged mice should show larger GABA transients [6].
• Chemogenetically suppress plPFC‑CeA BDNF release in aged mice; this should raise pCREB, increase CeA excitability, and reinstate a positive amygdala‑anxiety correlation measured via fMRI BOLD signal during anxiety‑provoking tasks.
• Overexpress CREB selectively in CeA CRF neurons of aged mice via AAV‑CreB; predict recovery of Grin1‑dependent fear consolidation (enhanced freezing) and reversal of the negative amygdala‑anxiety correlation seen in aged humans [1][3].
• Pharmacologically block GABA‑A receptors in CeA (e.g., with bicuculline) during extinction in aged animals; this should impair extinction and increase anxiety‑like behavior, mimicking the young phenotype.

Falsifiability If aged mice show no difference in pCREB, GABA tone, or plPFC‑CeA BDNF signaling compared with young mice, or if manipulating CREB does not alter the amygdala‑anxiety coupling, the hypothesis is refuted. Conversely, confirming any of the predicted directional changes supports the model.

Broader Impact Linking molecular CREB state to circuit‑level GABAergic rewiring offers a mechanistic bridge between cellular aging processes and systems‑level emotional regulation, suggesting that targeted modulation of CREB‑dependent inhibitory pathways could restore adaptive anxiety responses in older adults without compromising threat detection.