Cholecystokinin-immunoreactive neurons in rat and monkey cerebral cortex make symmetric synapses and have intimate associations with blood vessels.

Neurons displaying cholecystokinin-like immunoreactivity (CCK neurons) in rat and monkey cerebral cortex were examined by light and electron microscopic immunocytochemistry. CCK neurons were found to be mainly bipolar cells present in all layers and in all areas of the rat cerebral cortex. CCK neurons were also found in all regions examined in monkey cortex (pre- and post-central gyri and superior parietal lobule). The somata and the dendritic processes of CCK neurons receive relatively few synapses but both symmetric and asymmetric axosomatic and axodendritic synapses were found. The majority of axon terminals displaying CCK-like immunoreactivity formed symmetric synapses, most frequently with the somata and proximal dendrites of pyramidal and nonpyramidal neurons. The somata and processes of CCK neurons were also found to establish very close nonsynaptic associations with blood vessels and with other neurons, suggesting possible roles for the peptide in the maintenance of neuronal excitability and cerebral blood flow.