Allopregnanolone mediates affective switching through modulation of oscillatory states in the basolateral amygdala
Brexanolone (allopregnanolone), was recently approved by the FDA for the treatment of post-partum depression, demonstrating long-lasting antidepressant effects. Despite our understanding of the mechanism of action of neurosteroids as positive allosteric modulators (PAMs) of GABAO_SCPLOWAC_SCPLOW receptors, we still do not fully understand how allopregnanolone exerts these persistent antidepressant effects. Here, we demonstrate that allopregnanolone and similar synthetic neuroactive steroid analogs, SGE-516 (tool-compound) and zuranolone (SAGE-217, investigational-compound), are capable of modulating oscillatory states across species, which we propose may contribute to long-lasting changes in behavioral states. We identified a critical role for interneurons in generating oscillations in the basolateral amygdala (BLA) and a role for delta-containing GABAO_SCPLOWAC_SCPLOWRs in mediating the ability of neurosteroids to modulate network and behavioral states. Actions of allopregnanolone in the BLA is sufficient to alter behavioral states and enhance BLA high-theta oscillations (6-12Hz) through delta-containing GABAO_SCPLOWAC_SCPLOW receptors, a mechanism distinct from other GABAO_SCPLOWAC_SCPLOW PAMs, such as benzodiazepines. Moreover, treatment with the allopregnanolone analog SGE-516 induces long-lasting protection from chronic stress-induced disruption of network states, which correlates with improved behavioral outcomes. Our findings demonstrate a novel molecular and cellular mechanism mediating the well-established anxiolytic and antidepressant effects of neuroactive steroids.