Interactions between Distinct GABA A Circuits in Hippocampus

Abstract

Synchronous activity among synaptically connected interneurons is thought to organize temporal patterns such as gamma and theta rhythms in cortical circuits. Interactions between distinct interneuron circuits may underlie more complex patterns, such as nested rhythms. Here, we demonstrate such an interaction between two groups of CA1 interneurons, GABA A,slow and GABA A,fast cells, that may contribute to theta and gamma rhythms, respectively. Stratum lacunosum-moleculare (SL-M) stimuli that activate GABA A,slow inhibitory postsynaptic currents (IPSCs) in pyramidal cells simultaneously depress the rate and amplitude of spontaneous GABA A,fast IPSCs for several hundred milliseconds. This suppression has a similar pharmacological profile to GABA A,slow IPSCs, and SL-M stimuli elicit GABA A,slow IPSCs in interneurons. We conclude that GABA A,slow cells inhibit both pyramidal cells and GABA A,fast interneurons and postulate that this interaction contributes to nested theta/gamma rhythms in hippocampus.