Dopamine Synthesis from L-Tyrosine by Non-Dopaminergic Neurons in Co-Operation
Since the development of the histofluorescence technique for detection of catecholamines (Björklund and Lindvall, 1984) and then of immunostaining for tyrosine hydroxylase (TH) (Hökfelt at al., 1984), the neurons showing fluorescence or possessing TH were considered as catecholaminergic neurons. Later, neurons possessing only one of the enzymes of dopamine (DA) synthesis, TH or aromatic L-amino acid decarboxylase (AADC), were discovered (Meister et al., 1988). Although the number of monoenzymatic neurons greatly exceeds that of bienzymatic DAergic neurons (Björklund and Lindvall, 1984; Van den Pol et al., 1984) and they are widely distributed in the brain (Meister et al., 1988; Ikemoto et al., 1998), the functional significance of the former remains uncertain. Arcuate nucleus (AN) is considered as a promising model to approach this problem since it contains neurons expressing only TH (Meister et al., 1988; Okamura et al., 1988a) and most probably the neurons possessing only aromatic L-amino acid decarboxylase (AADC) (Krajnak and Nunez, 1996). On the other hand, the AN is the functionally important DAergic system, and DA produced in this region inhibits prolactin secretion (McCann et al., 1984). This paper summarizes our recent data on the development and functional significance of monoenzymatic TH- or AADC-expressing neurons in the AN of male rats during ontogenesis.
KeywordsTyrosine Hydroxylase Median Eminence Arcuate Nucleus Dopamine Synthesis DAergic Neuron
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