Colocalization of parvalbumin and calbindin D-28k in neurons including chandelier cells of the human temporal neocortex

Chandelier cells are cortical GABAergic interneurons with a unique synaptic specificity enabling them to exert a strong inhibitory influence on pyramidal cells. By using immunocytochemistry for the calcium-binding protein calbindin D-28k in the human temporal neocortex, we have found numerous immunoreactive processes that were identified as chandelier cell axon terminals. This was a striking find since in previous immunocytochemical studies of the primate neocortex, chandelier cell axon terminals had been shown to be immunoreactive for another calcium-binding protein, parvalbumin, and colocalization studies indicate that parvalbumin and calbindin are present in almost completely separate neuronal populations. Here, we present double-label immunofluorescence experiments showing that parvalbumin and calbindin immunoreactivities are colocalized in certain neurons that include a subpopulation of chandelier cells whose cell bodies are located mainly in layers V and VI of the human temporal neocortex. The results suggest a selective laminar distribution of neurochemical subtypes of chandelier cells which is a peculiar feature of the organization of the human neocortex.