Physiological and morphological identification of somatostatin- or vasoactive intestinal polypeptide-containing cells among GABAergic cell subtypes in rat frontal cortex

Martinotti cells are Sst-expressing interneurons with an axonal plexus in L1 that targets tuft dendrites of pyramidal cells, including synapses on spines.

“we broadly define Martinotti cells as Sst expressing INs with a plexus of axon in L1, where it is known to target the tuft dendrites of pyramidal cells, including making synapses on spines”

Sst interneurons are dendritic targeting, unlike PV interneurons.

“In contrast to PV INs, Sst INs are dendritic targeting”

These interneurons likely correspond to small CCK basket cells, which have a local axonal arbor, in contrast to the vertically oriented translaminar axonal arbor of Vip bipolar cells.

“These INs likely correspond to what has been referred to as small CCK basket cells, which, in contrast to the typical vertically oriented translaminar axonal arbor of the Vip bipolar cells, have a rather local axonal arbor (Freund et al., 1986; Kawaguchi and Kubota, 1996; Kubota, 2014; Wang et al., 2002).”

In addition to irregular spiking, bursting and strongly adapting Vip cells have been reported.

“In addition to irregular spiking, bursting and strongly adapting Vip cells have been reported (Cauli et al., 2000; Kawaguchi and Kubota, 1996; Lee et al., 2010; Porter et al., 1998; Pronneke et al., 2015).”

Bipolar Vip interneurons in deeper layers have dendrites spanning both supra- and infragranular layers, but their axons are restricted to layers 5/6, unlike layer 2/3 Vip interneurons.

“In contrast, Vip INs in deeper layers had dendrites spanning both supra- and infragranular layers, but had their axons restricted to L5/6 (Kawaguchi and Kubota, 1996; Pronneke et al., 2015).”

The study identifies 13 Sst met-types, substantially more than reported in previous morphological and/or electrophysiological studies.

“We identify 13 Sst met-types (Figure 6), which is substantially more than described in previous morphological and/or electrophysiological studies (Kawaguchi and Kubota, 1996; McGarry et al., 2010; Markram et al., 2015; Jiang et al., 2015; Munõz et al., 2017).”

The neocortical homolog of the O-LM cell is the Martinotti cell typically encountered in layers 2/3 and 5/6 with ascending axon forming a plexus in layer 1 targeting the distal dendritic tufts of pyramidal cells.

“The neocortical homolog of the O-LM cell is the Martinotti cell typically encountered in layers 2/3 and 5/6 with ascending axon forming a plexus in layer 1 targeting the distal dendritic tufts of pyramidal cells (569, 571, 1134, 1154, 1192).”

The defining molecular characteristic of mature O-LM, HIPP, and Martinotti cells is the expression of SST.

“The defining molecular characteristic of mature O-LM, HIPP, and Martinotti cells is the expression of SST (FIGURE 3C) (352, 571, 581, 716, 721, 862, 980, 1134, 1154).”