TEMPORAL AND SPATIAL DEVELOPMENT OF SEROTONIN AND DOPAMINE NEURONS INTHE DROSOPHILA CNS

We present a high-resolution profile of the temporal and spatial immun oreactivity for dopamine and serotonin in the Drosophila embryonic CNS and the expression pattern of two enzymes important in their biosynth esis, DOPA decarboxylase (DDC) and tyrosine hydroxylase (TH). DDC perf orms the final catalytic step in the synthesis of both biogenic amines and TH is the rate-limiting enzymatic step in the synthesis of dopami ne. We show that the DDC-expressing neurons synthesize either serotoni n or dopamine, but not both, and that the two neuronal subtypes follow similar axonal pathways. In addition, we describe two DDC-expressing cell types that do not synthesize detectable levels of serotonin or do pamine. We also describe a novel set of TH-expressing neurons that are detected only during embryogenesis. The initial appearance of both en zymes and their metabolites during embryogenesis shows unexpected dive rsity. The onset of Ddc expression is heterogeneous, such that certain classes of cells express high levels of DDC several hours before othe rs. High levels of TH immunoreactivity are observed at a time when DDC immunoreactivity is barely detectable. Despite low levels of DDC, bot h dopamine and serotonin are first detected at the earliest stages of DDC expression. We discuss the implications of these observations in t he differentiation of dopamine and serotonin neurons. (C) 1994 Academi c Press, Inc.