Regional distribution of catecholamines in monkey cerebral cortex, evidence for a dopaminergic innervation of the primate prefrontal cortex

The regional distribution of dopaminergic and noradrenergic innervations in the monkey cerebral cortex was evaluated using radioenzymatic determinations of dopamine (DA) and noradrenaline (NA). Of the 22 cortical areas assayed the highest DA/NA ratios, above 0.4, were found in the areas of the frontal lobe innervated by the mediodorsal thalamic nucleus, i.e. the prefrontal cortex. This ratio was higher than that in the cingulate (‘limbic’) cortex. Primary sensory areas and the hippocampus had the lowest ratio. Since a high DA/NA ratio indicates an independent dopaminergic innervation, we conclude that the dopaminergic afferents in the monkey neocortex preferentially terminate in the prefrontal area. The distribution of NA was different from that of DA, the highest values being found in the sensorimotor and cingulate cortices, and in the septum.