PT  - JOURNAL ARTICLE
AU  - Nigro Maximiliano José
AU  - Yoshiko Hashikawa
AU  - Bernardo Rudy
TI  - Diversity and connectivity of layer 5 somatostatin-expressing interneurons in the mouse barrel cortex
AID  - 10.1523/JNEUROSCI.2415-17.2017
DP  - 2018 Jan 11
TA  - The Journal of Neuroscience
PG  - 2415-17
4099  - http://www.jneurosci.org/content/early/2018/01/11/JNEUROSCI.2415-17.2017.short
4100  - http://www.jneurosci.org/content/early/2018/01/11/JNEUROSCI.2415-17.2017.full
AB  - Inhibitory interneurons represent 10-15% of the neurons in the somatosensory cortex, and their activity powerfully shapes sensory processing. Three major groups of GABAergic interneurons have been defined according to developmental, molecular, morphological, electrophysiological, and synaptic features. Dendritic-targeting somatostatin-expressing interneurons (SST-INs) have been shown to display diverse morphological, electrophysiological and molecular properties and activity patterns in vivo. However, the correlation between these properties and SST-IN subtype is unclear. In this study we aimed to correlate the morphological diversity of layer 5 (L5) SST-INs with their electrophysiological and molecular diversity in mice of either sex. Our morphological analysis demonstrated the existence of three subtypes of L5 SST-INs with distinct electrophysiological properties: T-shaped Martinotti cells innervate L1, and are low-threshold spiking; fanning-out Martinotti cells innervate L2/3 and the lower half of L1, and show adapting firing patterns; non-Martinotti cells innervate L4, and show a quasi-fast spiking firing pattern. We estimated the proportion of each subtype in L5 and found that T-shaped Martinotti, fanning-out Martinotti and Non-Martinotti cells represent ∼10, ∼50 and ∼40% of L5 SST-INs, respectively. Lastly we examined the connectivity between the three SST-IN subtypes and L5 pyramidal cells (PCs). We found that L5 T-shapped Martinotti cells inhibit the L1 apical tuft of nearby PCs; L5 fanning-out Martinotti cells also inhibit nearby PCs but they target the dendrite mainly in L2/3. On the other hand non-Martinotti cells inhibit the dendrites of L4 neurons while avoiding L5 PCs. Our data suggest that morphologically distinct SST-INs gate different excitatory inputs in the barrel cortex.SIGNIFICANCE STATEMENTMorphologically diverse layer 5 SST-INs show different patterns of activity in behaving animals. However, little is known about the abundance and connectivity of each morphological type and the correlation between morphological subtype and spiking properties. We demonstrate a correlation between the morphological and electrophysiological diversity of layer 5 SST-INs. Based on these findings we built a classifier to infer the abundance of each morphological subtype. Lastly, using paired recordings combined with morphological analysis, we investigated the connectivity of each morphological subtype. Our data suggest that, by targeting different cell types and cellular compartments, morphologically diverse SST-INs might gate different excitatory inputs in the mouse barrel cortex.