A review of the neuroembryology of monoamine systems

The technique of monoamine histofluorescence has been used successfully for neuroembryologic studies in a number of species ranging from amphibia to the human. Monoamine systems can be visualized early, often before final cell division and migration have taken place. Neuronal cell bodies are seen before axon terminals. Unlike the adult animal, preterminal axons can often be visualized, even in the untreated animal. Anatomical studies have shown major analogies in most of the species studied. CA-containing neuronal cell bodies are restricted to the brainstem and hypothalamus. Those neurons containing 5-HT are largely restricted to the brainstem raphe, although other cell groups may take up 5-HT, or related compounds, under experimental conditions. Monoamine nerve terminals are found throughout the entire nervous system, with some of the regions of highest density being the hypothalamus and striatum. Dynamic studies have indicated that biochemical differentiation precedes morphologic maturity, often by a long period of time. Although attempts have been made to determine a specific role of monoamines in the complex programs of neurogenesis, there is little specific data currently available.