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Review
. 2016 Jul;17(7):401-9.
doi: 10.1038/nrn.2016.53. Epub 2016 May 26.

Somatostatin-expressing neurons in cortical networks

Joanna Urban-Ciecko  1 , Alison L Barth  1
Affiliations
Review

Somatostatin-expressing neurons in cortical networks

Joanna Urban-Ciecko et al. Nat Rev Neurosci. 2016 Jul.

Abstract

Somatostatin-expressing GABAergic neurons constitute a major class of inhibitory neurons in the mammalian cortex and are characterized by dense wiring into the local network and high basal firing activity that persists in the absence of synaptic input. This firing provides both GABA type A receptor (GABAAR)- and GABABR-mediated inhibition that operates at fast and slow timescales. The activity of somatostatin-expressing neurons is regulated by brain state, during learning and in rewarded behaviour. Here, we review recent advances in our understanding of how this class of cells can control network activity, with specific reference to how this is constrained by their anatomical and electrophysiological properties.

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Conflict of interest statement

Competing interests statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Three-dimensional morphological reconstructions of SST interneurons in the primary somatosensory cortex of different transgenic mouse lines. Somatostatin-expressing (SST) neuron diversity is highlighted by the differences in anatomical properties of cells within and across layers. Cell bodies and dendrites are shown in blue, and axons are shown in red. The three arrowheads in the top row point to a turning point of the axon, from the upper layers back to layer 4 (L4). The top panel shows neurons in the X94 line. The bottom panel shows neurons in the green fluorescent protein (GFP)-expressing inhibitory neuron (GIN) line and in the X98 line. Note that in the GIN and X98 lines, both L2/3 and L5 SST neurons have an axonal branch that ascends and prominently elaborates in L1, as well as substantial branching within the ‘home’ layer that contains the cell body. L4 SST neurons may also have an axonal branch that ascends to L1, although most of the axon is concentrated in L4. This selective axonal targeting to L1 is similar to that observed in hippocampal stratum oriens–lacunosum moleculare (OLM) neurons, in which the SST cell body lies in the stratum oriens, and the axon elaborates in the lacunosum moleculare. Dense, lamina-specific axons from SST neurons suggest an important role for these cells in regulating synapses that lie within this layer through either GABA type A receptor (GABAAR)- or GABABR-mediated mechanisms. Figure is republished with permission of Society for Neuroscience, from Distinct subtypes of somatostatin-containing neocortical interneurons revealed in transgenic mice. Ma, Y., Hu, H., Berrebi, A. S., Mathers, P. H. & Agmon, A., J. Neurosci. 26 (19) 5069–5082 (2006); permission conveyed through Copyright Clearance Center, Inc.
Figure 2
Figure 2
Regulation of SST-neuron activity during movement and sensation. The activity of somatostatin-expressing (SST) neurons can be up- or downregulated during different activities and behaviours, and in response to different stimuli. a | Schematic of the configuration (left panel) used for in vivo whole-cell recording (right panel; red trace) from a layer 2/3 (L2/3) SST neuron from mouse barrel cortex, during periods of quiet resting or whisking activity (right panel; blue trace). Whisking is associated with hyperpolarization of the SST neuron. b | Schematic of the calcium imaging configuration (left panel) used for the whole-field measurement of calcium transients in different cell types in different layers of the hippocampus — in this case, SST neurons with cells bodies in the stratum oriens–alveus (OA) that project to the stratum lacunosum moleculare (LM), known as OLM cells. Example trials (right panel) of Ca2+ transients in the LM during sensory stimuli and locomotion show that SST neurons increase their activity during presentation of the unconditioned stimulus (an aversive air-puff), but not to other sensory stimuli or during locomotion. PYR, stratum pyramidale; RAD, stratum radiatum; Vm, membrane potential. Part a is adapted from REF. , Nature Publishing Group. Part b is from Lovett-Barron, M. et al. Dendritic inhibition in the hippocampus supports fear learning. Science 343, 857–863 (2014); reprinted with permission from AAAS.
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