Anterograde Axonal Tract Tracing

Deficits in sensory and motor function after spinal cord injury (SCI) are attributable primarily to the interruption of long sensory and motor axonal tracts in the spinal cord. How to exquisitely label these tracts within the spinal cord and their connections to the brain or periphery continues to be an important concern for SCI research. Axonal tract tracing technologies are powerful tools for identifying axonal connections in the normal or injured spinal cord. With appropriate injury models and tracing techniques, status of axons such as sparing, die-back, sprouting, regeneration, or synaptogenesis can be readily identified. The tracing techniques can also be used to determine axonal projections from neurons that are grafted into the lesion site. For anterograde tracing, tracers are transported by attaching to different vectors with different speed from the soma to axon terminal. After tracing, tissue is collected following appropriate survival time. To detect tracers along axons or at their terminals, various labeling techniques are used which include direct fluorescence, immunohistochemistry, immunofluorescence, and autoradiography. When combined with retrograde tracing techniques, anterograde tracers may be used to establish anatomical reorganizations of neural networks. When combined with immunohistochemistry, anterograde tracing may be used for neurochemical characterization of specific neuronal pathways or specific cell types.