Figure 6. Target‐cell specificity of frequency‐dependent synaptic transmitter release from pyramidal cell terminals.

A, simultaneous whole‐cell recording from three neurons. Their somata and dendrites were reconstructed. Cell types are shown in different colours; the presynaptic excitatory pyramidal cell is blue, and the two inhibitory target cells are in red and green, respectively. Scalebar: 50 μm. B, differential interference contrast photomicrograph of a pyramidal cell (left) and two types of inhibitory cells (middle and right) located in the supragranular cortical layer. Scalebar: 10 μm. C, target‐cell dependence of EPSP amplitudes recorded simultaneously in two inhibitory target cells. The EPSPs were evoked by repetitive APs evoked in the pyramidal cell. Note the difference in frequency‐dependent response amplitudes in the two target cells. D, columnar layers and projection of L5tt cells located in layer 5B to two types of excitatory target cells, in the cortex (L5tt cells in the same column) and in the thalamus [principal cells in the posteromedial nucleus of the thalamus (POm)], respectively. E, upper panel shows a paired whole‐cell voltage recording from two L5tt cells illustrating slight frequency‐dependent facilitation of EPSP amplitude in the L5tt target cell. Lower panel is a recording of EPSCs from a POm principal cell. There is strong frequency‐dependent amplitude depression during repetitive stimulation of individual giant boutons of a L5tt cell, forming a giant synapse on the thalamic POm cell. Modified from Reyes et al. (1998), Reyes & Sakmann (1999) and Groh et al. (2008).