Cell-autonomous GABAARs are essential for NMDAR-mediated synaptic transmission, LTP, and spatial memory.

GABA(A) receptors (GABA(A)Rs) mediate most synaptic inhibition in the brain, but their cell-autonomous role in regulating glutamatergic transmission remains poorly understood. By targeting GABA(A)R β1-3 subunit alleles (GABRB1-3) at once, we genetically eliminated GABA(A)Rs in individual hippocampal CA1 pyramidal neurons. We find that single-cell silencing of GABAergic transmission does not alter AMPAR-mediated synaptic transmission, but leads to a reduction in NMDAR-mediated synaptic transmission, loss of long-term potentiation (LTP), and impaired spatial memory. Genetic rescue experiments reveal that NMDAR-mediated whole-cell currents and synaptic transmission depend on specific GABA(A)R subtypes and are tightly regulated by neuronal excitability. Pharmacologically restoring NMDAR function in β123-CRISPR mice rescues both LTP and spatial memory deficits induced by the loss of GABA(A)Rs in CA1 neurons. Our data uncover a previously unknown regulation of synaptic NMDAR functions by GABA(A)Rs at the single-cell level and provide insight into excitation and inhibition balance between GABA(A)Rs and NMDARs in the brain.