SST and major depressive disorder: Interestingly, this alteration in GABAergic signaling in MDD subjects appears to be restricted to interneuron subtypes that project to the dendritic compartment of cortical pyramidal cells, as characterized by the expression of somatostatin (SST), neuropeptide Y (NPY) and cortistatin (CORT) neuropeptides (and that co-express calbindin); Cells targeting the perisomatic compartment, such as parvalbumin (PV)- or cholecystokinin (CCK)-expressing GABA neurons appear only sparingly affected (Sibille et al., 2010; Tripp et al., 2011; Guilloux et al., 2012).