ABSTRACT

The main monoaminergic systems in the central nervous system (CNS) are the following: histamine, dopamine, norepinephrine [noradrenaline (NA)], epinephrine (adrenaline), serotonin (5-HT), and melatonin. Relevant to the human pathological condition known as “major depression” are the dopaminergic, noradrenergic, and serotonergic systems (Figure 5.1). The development of these systems is in a region around the mid-hindbrain border and may rely on shared molecular mechanisms, although the ˜nal terminal differentiation is acquired through the recruitment of speci˜c factors (Goridis and Rohrer 2002). Transmitter synthesis relies on the conversion of the amino acids tyrosine and tryptophan, which will lead to dopamine, noradrenaline, and 5-HT, respectively (Goridis and Rohrer 2002). Some of the enzymes that perform the conversion are required by all the pathways [like l-aromatic amino acid decarboxylase (Aadc)] and are therefore present in all different neuronal groups. The dopamine and noradrenaline syntheses share the ˜rst two steps of the pathway since noradrenaline is generated by dopamine-β-hydroxylase (Dbh). These two neuronal groups therefore share the enzymes tyrosine hydroxylase (Th) and Aadc, whereas the latter group additionally contains Dbh.