Anterograde transsynaptic transport of WGA-HRP from spinal afferents to postganglionic sympathetic cells of the stellate ganglion of the guinea pig.

After injection of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) or choleragenoid conjugated HRP (B-HRP) into lower cervical and upper thoracic dorsal root ganglia (DRG), HRP reaction product was observed in peripheral fibers of spinal afferents and in postganglionic cell bodies of the stellate ganglion (SG) in the guinea pig. After WGA-HRP injection into C8-T3 or T5 DRG, HRP-labelled cells were observed to cluster at the rami within the SG, with peak labelling observed 36 h after injection. SG cell labelling occurred with B-HRP as well, but not with native HRP after injection into thoracic DRG. Injection of this tracer in C8 DRG gave rise to a small number of labelled cells. In contrast to the labelling pattern following thoracic or C8 DRG injections, injection of WGA-HRP or native HRP into C6 DRG, led to random SG cell labelling. We conclude that the anterograde transsynaptic transport, following injection of WGA-HRP into thoracic DRG, provides a method to selectively label a population of postganglionic sympathetic neurons within the SG. A combination of transsynaptic and retrograde transport appears to be responsible for labelling after injection into C8 DRG, whereas labelling after C6 DRG injections seems to be due primarily to retrograde transport.