The Current Status of Somatostatin-Interneurons in Inhibitory Control of Brain Function and Plasticity

Figure 1

SST-interneurons labeled in X98-, GIN-, and X94-transgenic mice have distinct laminar distributions and wiring patterns. X98-SST-interneurons mainly reside in infragranular layer V whereas the GIN-SST-interneuron subpopulation 1 mainly resides in supragranular layer II/III. Both subtypes are considered Martinotti cells due to their layer I dendrite-targeting properties onto layer II/III and V pyramidal neurons. The second and third population of GIN-SST-interneurons avoid layer I but dendritically target pyramidal neurons within layer II/III. GIN-type 2 interneurons are characterized by small, multipolar dendritic arbors, whereas GIN-type 3 interneurons have larger, bitufted dendritic arbors. Some layer II/III GIN-SST-neurons target the axon initial segment of pyramidal neurons. The dotted line denoting this synapse indicates that it is not yet known to which subpopulations this property can be attributed. Layer II/III VIP-interneurons somatically target SST-interneurons within this layer. X94-SST-interneurons reside either in layer IV, where they mainly target fast-spiking PV-interneurons, or in layer V, where they dendritically target layer V pyramidal neurons. Specifically layer V X94-neurons can receive thalamic input, whereas layer IV X94-neurons are intracortically driven. Finally, SST-projecting-neurons are mainly described in layer VI. Thick lines indicate dendritic arbors; thin lines depict axonal projections. Black dots indicate synapses between SST-interneuron dendrites and their targets. Grey dots indicate synapses from the input sources onto SST-interneurons.