FIGURE 13.

The three modes of GABA release from PV-containing, CCK-containing and NGFC interneurons. A and B: superimposed IPSCs (black) evoked by single presynaptic action potentials (red) in a PV-containing interneuron-granule cell (GC) pair (A) and a CCK interneuron-granule cell pair (B). Insets: histograms of IPSC latency. A and B, bottom panels: superimposed IPSCs (black) evoked by trains of 10 action potentials (red) in a PV interneuron-granule cell pair (left) show a predominant synchronous mode of inhibitory output. In contrast, repetitive transmission in a CCK interneuron-granule cell pair (right) shows a large asynchronous component of transmission as the train proceeds. Green: average IPSCs. Insets: presynaptic action potentials aligned to the stimulus onset at expanded time scale (scale bars: 2 ms, 50 mV). C: GABA_A IPSCs evoked by NGFCs (top right panel) are comparatively slower than those observed at FSBC synapses. Top: 10 consecutive IPSCs (gray) and their average (black) in a layer 2/3 PC after single action potentials in a layer 1 NGFC (top). Middle traces show equivalent IPSCs evoked by a layer 2 FSBC for comparison. Bottom right panel: comparison of the kinetics of postsynaptic responses evoked by NGFCs (black squares) and FSBCs (gray circles). Each point represents an individual connection. D: modulation of GABA responses evoked by NGFCs by GABA uptake. Fast IPSCs evoked from FSBC are not sensitive to the GABA uptake inhibitor NO711. In contrast, GABA_A,slow IPSCs arising from NGFCs are markedly prolonged in the presence of NO711, demonstrating a differential sensitivity of the two modes of transmission to inhibition of GABA uptake. [A and B from Hefft and Jonas (477) with permission from Nature Neuroscience. C and D from Szabadics et al. (1074).]