PSA-NCAM immunoreactivity in chandelier cell axon terminals of the human temporal cortex

In the adult central nervous system, the expression of polysialylated forms of the cell-surface glycoprotein NCAM (PSA-NCAM) is thought to be confined to areas particularly susceptible to plastic changes. In the present study, PSA-NCAM was found to be expressed in the somata, dendrites and axonal processes of some neurons, including cartridge-like elements, which according to our criteria, were identified as chandelier cell axon terminals (chandelier terminals), in the adult human entorhinal cortex and neocortex. These chandelier terminals were very numerous in layers II and III, whereas in deeper layers they were found only occasionally. Double immunocytochemical staining for PSA-NCAM with parvalbumin (PV), with GABA transporter (GAT-1) or with the 5-HT(1A) serotonin receptor allowed us to verify them as true chandelier terminals. Nearly all (92-95%) PV-immunoreactive (-ir) and GAT-1-ir chandelier terminals in layers II and III coexpressed PSA-NCAM. Most of the PSA-NCAM-ir chandelier terminals (89-98%) were also labeled for PV and GAT-1. The results suggest that chandelier terminals in layers II and III of the human entorhinal cortex and temporal neocortex might be particularly susceptible to plastic changes.