Cholecystokinin- and dopamine-containing mesencephalic neurons provide distinct projections to monkey prefrontal...

Retrograde transport and immunohistochemical techniques were utilized to determine if cholecystokinin (CCK)-containing neurons of the primate ventral mesencephalon project to prefrontal cortex, and to examine what relation the CCK innervation of prefrontal cortex bears to the dopaminergic projection to this region. Following injections of Fast blue into monkey prefrontal cortex, retrogradely labeled, CCK-positive neurons were observed predominantly in rostromedial portions of the ventral mesencephalon; these CCK-containing projection neurons were not immunoreactive for tyrosine hydroxylase. Furthermore, dual-labeling studies in the prefrontal cortex revealed that CCK and tyrosine hydroxylase were present in separate populations of axons. These results demonstrate that the CCK innervation of monkey prefrontal cortex arises from both intrinsic and extrinsic sources; in contrast to the rat, the extrinsic CCK innervation of monkey prefrontal cortex is distinct from the dopaminergic mesocortical projection.