Negative allosteric modulation of α5-GABA(A) receptors engages dynamic cortical glutamatergic and GABAergic mechanisms underlying adaptive behavior in mice.

Chronic stress disrupts glutamatergic and GABAergic plasticity in the medial prefrontal cortex (mPFC), impairing circuit integration and contributing to the pathophysiology of stress-related disorders, such as Major Depressive Disorder (MDD). Rapid-acting antidepressants like ketamine can rapidly reverse these deficits, but its clinical use is limited by psychotomimetic side effects. Notably, the α5-GABA(A)R negative allosteric modulator (α5-NAM) Basmisanil (BSM), reproduces ketamine-like behavioral outcomes in preclinical models, although the cellular mechanisms underlying its actions remain unclear. Here, we investigated whether BSM promotes ketamine-like enhancement of cortical plasticity and engages cell type-specific mechanisms to support adaptive behaviors over time. We show that BSM produced rapid and sustained facilitation of motivational, hedonic, and active coping behaviors via mPFC circuits. BSM induced c-Fos expression in mPFC D1R- and somatostatin-expressing cells, suggesting activation of specific subsets of pyramidal and GABA interneurons. In both mPFC and hippocampus, BSM rapidly activated Erk- or Akt-mTOR signaling pathways as well as increased synaptic proteins critical for glutamatergic and GABAergic function. BSM also reversed maladaptive behaviors induced by chronic unpredictable stress, including impairment in object recognition memory and social interaction. Finally, chemogenetic silencing of mPFC CaMKII-expressing neurons blocked both rapid and sustained actions of BSM, whereas inhibition of mPFC GABA interneurons reversed only long-term behavioral outcomes. These results indicate that α5-GABA(A)R modulation requires early activation of pyramidal neurons to drive rapid plasticity, while GABAergic adaptations support sustained improvements. This dynamic mechanism restores excitation-inhibition (E/I) balance and highlights GABAergic pathways as therapeutic targets for prefrontal dysfunction in stress disorders.