Development of the dopaminergic innervation in the prefrontal cortex of the rat.

The pre- and postnatal development of the dopaminergic innervation in the prefrontal cortex (PFC) of the rat is described from embryonic day 14 through postnatal day 90. By embryonic day 15 the dopamine (DA)-containing fibers reach the anlage of the lateral neocortex; 2 days later the first fibers have reached the subplate of the future prefrontal cortex. The process of entering the cortical plate starts just before birth. Prenatally, some dopaminergic fibers can be observed in the marginal zone of both the lateral and the medial wall of the hemisphere. Within 48 hours after birth a large number of dopaminergic fibers can be observed in the marginal zone, i.e., the future layer I, in some subareas of the PFC. A transient appearance of DA-positive fibers is noticed in the late embryonic and early postnatal periods especially in the marginal zone and possibly in the superficial layers of the pregenual cingulate cortex. Changes in the morphology of DA fibers at P4 suggest that the actual DA innervation starts at this age. From postnatal day 6 the different subareas of the PFC can be recognized according to the characteristics of the topographical distribution of the dopaminergic fibers. Until postnatal day 60 the density of the dopaminergic fibers continues to increase. No difference in density and topography was observed between postnatal days 60 and 90.