Cortical sources of CRF, NKB, and CCK and their effects on pyramidal cells in the neocortex

In order to investigate how neuropeptide transmission can modulate the neocortical network, we mapped the expression of neurokinin (NK) B, cholecystokinin (CCK), and corticotropin-releasing factor (CRF) and their receptors to neuronal types using patch-clamp and single-cell reverse transcription-polymerase chain reaction in acute slices of rat neocortex. Classification of neurons by unsupervised clustering based on the analysis of multiple electrophysiological and molecular properties disclosed 3 GABAergic interneuron clusters and 1 pyramidal cell cluster. The 3 neuropeptides were expressed in a cluster of interneurons characteristically expressing vasoactive intestinal peptide. CRF was additionally found in a cluster containing almost exclusively somatostatin-expressing interneurons, whereas CCK was present in all clusters. The respective receptors of these peptides, NK-3, CCK-B, and CRF-1, were essentially expressed in pyramidal cells. At -60 mV, pyramidal cells were weakly depolarized by each of these peptides. When pyramidal neurons were maintained to about 5 mV below spike threshold, depolarization induced by each peptide resulted in a long-lasting action potential discharge. Neuropeptide effects were prevented by selective antagonists of NK-3, CCK-B, and CRF-1 receptors. These results suggest that pyramidal neurons are the primary target of NKB, CCK, and CRF in the neocortex. They further indicate that specific interneuron types coordinate the release of these peptides and can induce a long-lasting increase of the excitability of the neocortical network.