Conjugates of horseradish peroxidase (HRP) with cholera toxin and wheat germ agglutinin are superior to free HRP as orthogradely transported markers.

The relative sensitivity of horseradish peroxidase (HRP) conjugates of cholera toxin (CTHRP) and wheat germ agglutinin (WGHRP) as orthogradely transported markers was compared with that of free HRP (FHRP) following unilateral, intravitreal injections of each probe in the rat. Both CTHRP and WGHRP labeled all of the recognized retinal efferents of the rat and were 30-50 times more sensitive than FHRP. In additional experiments the 'receptors' specificity of CTHRP and WGHRP was also demonstrated.