History and Future Directions of Tract-Tracing Techniques

Abstract

Tract tracing is one of the central topics of neuroanatomy. To elucidate the cells of origin, routes, and terminals of neural pathways, a variety of techniques have been developed including analysis of myelogenesis and demyelination, staining for degenerating myelin and axons, Golgi methods, and tracing using axonal transport and viral infections. To visualize normal morphology of a neural pathway, it is necessary to make constituent neurons incorporate as much reporter molecules as possible. Recent gene transfer techniques fulfill this requirement by making neurons produce reporter molecules themselves. Tract tracing using gene transfer is now combined with the control of neuronal activities by transgenes, and opened a new field of comprehensive analysis of morphology and functions of neural pathways.