Development of the nigrostriatal dopamine neuron and the pathways in the basal ganglia.

The nigrostriatal (NS) dopamine (DA) neuron and the basal ganglia show marked functional age variation in the first three decades. Neurohistochemical studies revealed marked age variation of activities of tyrosine hydroxylase at the terminal of the NS-DA neuron, which show exponential decremental variation from early childhood and subside in the fourth decade. DA-D2 receptors, examined by PET scan, are in high levels in the third decade which decrease dramatically to the bottom or 'adult' levels in the fourth decade. The examination of voluntary saccade suggested the striatal indirect pathways are functionally immature in the childhood and attain adult levels in around the middle of the second decade, while the striatal direct pathways have already been functionally matured in childhood. Clinical evidence suggests that among efferents of the basal ganglia those descending to the brainstem and the midbrain mature earlier while those ascending to the thalamus later. These developmental variation of the NS-DA neurons and the basal ganglia could modulate the ages at onset and clinical courses of the diseases with abnormalities in the NS-DA neuron or the basal ganglia which occur in these age periods.