Anatomical organization of dopamine systems in the normal human brain

ANATOMICAL ORGANIZATION OF DOPAMINE SYSTEMS IN THE NORMAL HUMAN BRAIN 

Dopamine is synthesized from the amino acid tyrosine by the enzymes tyrosine hydroxylase (TH which forms L-3,4-dihydroxylphenylalanine, l-DOPA) and L-amino acid decarboxylase (AADC) in dopaminergic neurons. The mRNA expression of the TH (which is the rate-limiting enzyme in the synthesis of dopamine) is abundant throughout the human mesencephalon (Fig. 1) TH is a phenotypic marker for all catecholamines, dopamine, noradrenaline and adrenaline. Evidence for the presence of TH has been documented in the mesencephalon from at least 4.5 to 7 weeks of human fetal life 

1976 Ilinsky et al., 1985 Russchen et al., 1987), the specific origin of the dopaminergic cell groups which specifically innervate the thalamus are still undefined. 

Overall, as predicted by anatomical organization and connectivity, the ventral tier nigrostriatal dopaminergic system is primarily associated with basal ganglia function related to motor behavior, whereas the dorsal tier mesocorticolimbic system is more linked to the neural structures involved in reinforcement, motivation, emotion and cognitive function. 

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