Comparison of synaptic and autaptic connections established by individual interneurons. A, Synaptic and autaptic connections of a layer IV DTC (soma and dendrites,red; axon, black) and a spiny stellate cell (soma and dendrites, green; axon not shown). The complete axonal and dendritic arborizations are shown by Tamás et al., (1997, their Fig. 6). The DTC innervated the spiny cell through three dendritic synapses (s1–s3) and established 32 autapses (a1–a32). Grouped numbersrepresent multiple autaptic junctions formed by the same bouton. Ten autapses were found on the soma, a higher proportion than the somatic targets (10.7%) in the overall synaptic target distribution.B, Synaptic and autaptic relationships between a layer IV DTC (soma and dendrites, red; axon,black) and a layer III–IV border pyramidal cell (soma and dendrites, green; axon, blue). The complete axonal and dendritic arborizations are shown by Buhl et al., (1997, their Fig. 1). The cell pair was in reciprocal synaptic connection, but only the effect of the pyramidal cell could be recorded. The DTC established nine autaptic junctions (a1–a9), innervated the pyramidal cell via 17 synapses (i1–i17), and received five synapses from the pyramid (p1–p5). Note that the subcellular distribution of synaptic and autaptic junctions established by the interneuron was similar on both cells.