Paired recordings from inhibitory basket cells connected to CA1 neurons at the stratum pyramidale reveal two classes of interneurons with fast and slow IPSC kinetics. A, Paired recordings from GABAergic basket cells connected to pyramidal neurons. B, A GABAergic basket cell (red) synaptically connected to a pyramidal neuron (blue). Biotin staining shows axon arbors predominantly located in stratum pyramidale (SP). SO, Stratum oriens; s.rad, stratum radiatum; SLM, stratum lacunosum-moleculare. C, All the examined connected pairs fall into two clusters according to the rise and decay times of the recorded IPSCs. Examples of IPSCs with fast and slow kinetics recorded from different interneuron types are shown on the left.