Retrograde tracing of enteric neuronal pathways

Neuroanatomical tracing techniques, and retrograde labelling in particular, are widely used tools for the analysis of neuronal pathways in the central and peripheral nervous system. Over the last 10 years, these techniques ha ve been used extensively to identify enteric neuronal pathways. In combinat ion with multiple-labelling immunohistochemistry, quantitative data about t he projections and neurochemical profile of many functional classes of cell s have been acquired. These data have revealed a high degree of organizatio n of the neuronal plexuses, even though the different classes of nerve cell bodies appear to be randomly assorted in ganglia. Each class of neurone ha s a predictable target, length and polarity of axonal projection, a particu lar combination of neurochemicals in its cell body and distinctive morpholo gical characteristics. The combination of retrograde labelling with targete d intracellular recording has made it possible to target small populations of cells that would rarely be sampled during random impalements. These neur oanatomical techniques have also been applied successfully to human tissue and are gradually unravelling the complexity of the human enteric nervous s ystem.