Cracking Down on Inhibition: Selective Removal of GABAergic Interneurons from Hippocampal Networks

nhibitory(GABAergic)interneuronsentrainassembliesofexcitatoryprincipalneuronstoorchestrateinformationprocessinginthehippocam-pus. Disrupting the dynamic recruitment as well as the temporally precise activity of interneurons in hippocampal circuitries can manifest inepileptiform seizures, and impact specific behavioral traits. Despite the importance of GABAergic interneurons during information encoding inthe brain, experimental tools to selectively manipulate GABAergic neurotransmission are limited. Here, we report the selective elimination ofGABAergic interneurons by a ribosome inactivation approach through delivery of saporin-conjugated anti-vesicular GABA transporter anti-bodies (SAVAs) in vitro as well as in the mouse and rat hippocampus in vivo. We demonstrate the selective loss of GABAergic-- but notglutamatergic--synapses, reduced GABA release, and a shift in excitation/inhibition balance in mixed cultures of hippocampal neurons ex-posed to SAVAs. We also show the focal and indiscriminate loss of calbindin, calretinin, parvalbumin/system A transporter 1, somatosta-tin, vesicular glutamate transporter 3 (VGLUT3)/cholecystokinin/CB1 cannabinoid receptor and neuropeptide Y local-circuitinterneurons upon SAVA microlesions to the CA1 subfield of the rodent hippocampus, with interneuron debris phagocytosed by infiltratingmicroglia. SAVA microlesions did not affect VGLUT1 excitatory afferents. Yet SAVA-induced rearrangement of the hippocampal circuitrytriggered network hyperexcitability associated with the progressive loss of CA1 pyramidal cells and the dispersion of dentate granule cells.Overall, our data identify SAVAs as an effective tool to eliminate GABAergic neurons from neuronal circuits underpinning high-order behaviorsand cognition, and whose manipulation can recapitulate pathogenic cascades of epilepsy and other neuropsychiatric illnesses