Postnatal development of tyrosine hydroxylase- and dopamine transporter-immunoreactive axons in monkey rostral entorhinal cortex.

Dopamine afferents from the mesencephalon appear to play a critical role in the normal development and cognitive functions of multiple areas of the primate cerebral cortex. In some regions, such as the prefrontal and motor cortices, dopamine innervation changes substantially during postnatal development. However, little is known about the postnatal maturation of dopamine afferents to the primate rostral entorhinal cortex, a periallocortical region that receives a dense dopamine innervation in adults. In this study, we used immunocytochemical techniques and antibodies against tyrosine hydroxylase and the dopamine transporter to examine the postnatal development of dopamine axons in the rostral subdivision of macaque monkey entorhinal cortex. Within animals, the axons labeled with each antibody did not differ in overall density or laminar distribution. Across development, the density of dopamine axons in layers I and VI did not change appreciably. In contrast, the density of labeled axons in layer III significantly increased by a factor of three between birth and 5-7 months of age. The timing of this change differs substantially from that observed in prefrontal cortex, where peak dopamine innervation occurs between 2 and 3 years of age. These findings, in concert with other data, suggest that developmental changes in the dopamine innervation of cortical regions may parallel the functional maturation of those areas.