Selective prefrontal cortical projections to the region of the locus coeruleus and raphe nuclei in the rhesus monkey.

Descending cortical projections to the region of the noradrenergic locus coeruleus (LC) and the serotonergic dorsal and central superior raphe nuclei were analyzed in the rhesus monkey using anterograde labeling techniques. HRP pellets or tritiated leucine were injected into one of 7 cortical areas: the dorsolateral prefrontal cortex, the dorsomedial prefrontal cortex, the orbital prefrontal cortex, the parietal association cortex, somatosensory cortex, the anterior portion of the inferior temporal gyrus, and the posterior portion of the inferior temporal gyrus. Anterogradely labeled fibers were found in and adjacent to the LC and raphe nuclei only following the dorsolateral and dorsomedial prefrontal cortical injections. Terminal labeling was densest at rostral levels of the LC, particularly in the area directly medial to the nucleus. Labeled fibers could not be followed beyond caudal levels of the LC. The projections to the contralateral LC and raphe nuclei were similar to, but less dense than that to the ipsilateral region. Injections into cortical areas other than the dorsal prefrontal cortex resulted in anterograde labeling of the pontine nuclei or pyramids, but not the LC/raphe region. These data, in conjunction with studies in the rat, suggest that the dorsal prefrontal cortex may be the only cortical area to have direct influence on the LC and raphe nuclei and secondary influence on the monoaminergic innervation of large areas of cerebral cortex.