Acetylcholine engages distinct amygdala microcircuits to gate internal theta rhythm

Acetylcholine (ACh) is released from basal forebrain cholinergic neurons in response to salient stimuli and engages brain states supporting attention and memory. These high ACh states are associated with theta oscillations, which synchronize neuronal ensembles. Theta oscillations in basolateral amygdala (BLA) underlie emotional memory, yet their mechanism remains unclear. Using brain slice electrophysiology in mice, we show large ACh stimuli evoke prolonged theta oscillations in BLA local field potential that depend upon activation of cholecystokinin (CCK) interneurons (INs). Somatostatin (SOM) INs inhibit CCK INs and are themselves inhibited by ACh, gating BLA theta. ACh-induced theta activity is more readily evoked in BLA over cortex or hippocampus, suggesting preferential activation of BLA during high ACh states. These data reveal a SOM-CCK IN circuit in BLA that gates internal theta oscillations and suggest a mechanism by which salient stimuli acting through ACh switch the BLA into a network state enabling emotional memory.