Enucleation-induced transsynaptic labeling with WGA-HRP in the developing rat visual system

Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) is a neuroanatomical tracer which is transported transneuronally. In order to investigate whether transport of WGA-HRP is across synapses, labeling was studied in the developing retinotectal pathway where it is known that enucleation results in increased ipsilateral synaptic connections from the remaining eye. While little or no transneuronal labeling was evident in controls, after enucleation transneuronal labeling was consistently observed. Furthermore, the critical period for enucleation-induced transneuronal labeling coincides with the known critical period for enucleation-induced neuronal survival and synaptic formation. The results suggest that transneuronal exchange of WGA-HRP depends on the presence of synapses, and is therefore transsynaptic.