Figure 2. An example of a pyramid to interneurone connection in rat.

In this example, the presynaptic layer 6 neurone (yellow soma/dendrites, white axon) was a corticothalamic-like pyramidal cell with an apical dendritic tuft in layer 4. The postsynaptic interneurone (red soma/dendrites, blue axon) was a bitufted, low-threshold spiking, dendrite-preferring interneurone. The interneurone also had an extensive axonal arbour in layer 4. The EPSP elicited by this connection was strongly facilitating with a paired pulse ratio > 3. Despite at least 6 (confirmed ultra-structurally) and possibly up to 12 synapses (visible as close membrane appositions at the microscopic level) mediating this connection, the failure rate in response to the first presynaptic spike of a train was > 30% (adapted from Fig. 4 of Deuchars & Thomson, 1995a).