Region‐specific distribution of catecholamine afferents in primate cerebral cortex: A fluorescence histochemical analysis

The density, laminar distribution, spatial orientation, and intrahemispheric pathways of norepinephrine (NE)- and dopamine (DA)- containing axons were analyzed in a wide range of cytoarchitectonically distinct areas of cerebral cortex in the adult rhesus monkey by fluorescence histochemistry. Although the boundaries between most areas were rarely sharp, there were marked regional differences in density and distribution of monoamine afferents in different cortical regions. Fibers exhibiting typical DA-like morphology were found only in the temporal and frontal lobes including motor and premotor areas as well as anterior cingulate and prefrontal cortices. In contrast, NE-containing axons were present in all cerebral lobes, with notably high density in the somatosensory area and low numbers in primary visual cortex. Intracerebral distribution was characterized by a network of large preterminal axons coursing both anteroposteriorly and mediolaterally in layer VI and in the subjacent white matter. In most cytoarchitectonic regions examined, catecholamine (CA)-containing axons exhibited a bilaminar distribution into one superficial and one deep fiber band. The location and width of the two dense bands, as well as the orientation and relative density of fibers within them, was region specific. Although fluorescent axons were found at all cortical depths, layers I, and IV usually contained relatively few fluorescent axons while layers II-III and IV-V were often densely innervated. An observation that may reflect a specialization in gyrencephalic brains is the particularly dense CA innervation around sulcal invaginations in all cerebral lobes. The present results confirm previous biochemical evidence of regional heterogeneity in the concentration of DA and NE in the primate neocortex (Brown and Goldman, '77:Brain Res. 124:576-550) an provide the first anatomical demonstration of corresponding differences in the pattern and density of CA innervation in diverse cytoarchitectonic areas in rhesus monkey. These findings raise the possibility of selective targets and functions for CA fibers in different layers and regions of the primate cortex.