GABA releases from parvalbumin-expressing and unspecific GABAergic neurons onto CA1 pyramidal cells are differentially modulated by presynaptic GABAB receptors in mouse hippocampus

Hippocampus CA1 pyramidal cells receive gamma-aminobutyric acid (GABA) release from multiple GABAergic interneurons. Combining optogenetic strategy and whole-cell recordings, we demonstrate that baclofen, a specific GABA(B) receptor agonist, depresses monosynaptic GABA(A) receptor-mediated transmission from parvalbumin (PV)-expressing interneuron terminals onto pyramidal cells with less efficacy than that from the unspecific GABAergic terminals. The depression from PV neuron terminals is mainly mediated by presynaptic P/N type calcium channels. The results suggest that GABA(B) receptors are widely expressed on GABAergic interneurons, where they exert inhibition onto pyramidal cells by GABA release with different efficacy. The data strengthen the proposal that diverse GABA neurons play different roles in modulating CA1 pyramidal cell excitability. (C) 2019 Elsevier Inc. All rights reserved.