Time of arrival of wheat germ agglutinin-HRP conjugates in superior colliculus after intraocular injections in the rat.

Rats received intravitreal injections of wheat germ agglutinin conjugated with horseradish peroxidase (WGHRP) or labeled with fluorescein isothiocyanate (WGFITC). SDS polyacrylamide gel electrophoresis of WGHRP demonstrated that little or no native horseradish peroxidase (HRP) was present in the injected conjugate. Under the conditions employed in these experiments, evidence for the orthograde transport of WGHRP but not of WGFITC was observed. In a separate experiment carried out under similar circumstances, WGFITC was retrogradely transported. Thus WGFITC does not appear to be a sensitive probe for studies of efferent projections. The earliest time of arrival of WGHRP in the contralateral superior colliculus (SC) was determined in order to establish the most rapid rate of anterograde transport of WGHRP. Retinal ganglion cell axon terminals in SC were first labeled 4 h after an intraocular injection of WGHRP which is equivalent to a transport rate of about 108 mm/day. This rate of transport is approximately half that reported for native HRP. It is concluded that the superior sensitivity of WGHRP over native HRP as an anterogradely transported marker cannot be ascribed to a more rapid rate of orthograde transport of WGHRP.