The trajectory of the intracortical noradrenergic fibers has been characterized by histochemical analysis following the production of cortical lesions in the rat. A large group of noradrenergic fibers enters the cortex at the frontal pole and proceeds caudally through the deep layers of dorsolateral cortex. Branches arise from these longitudinally directed fibers and form a uniform pattern of innervation throughout lateral cortex. Because these fibers travel long distances rostrocaudally within the gray matter, a large area of cortex can be deprived of noradrenergic innervation by a relatively small lesion affrontal cortex. The medial and lateral cortex can be selectively and differentially denervated of noradrenergic fibers, and there is a medial to lateral topographic relationship between deep longitudinally running fibers and overlying cortex.
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