The proportion of neurons in the rat neostriatum that project to the substantia nigra demonstrated using horseradish peroxidase conjugated with wheatgerm agglutinin.

Following the injection of small volumes of horseradish peroxidase conjugated with wheatgerm agglutinin into the substantia nigra of the rat, a high proportion of the total neuronal population in parts of the ipsilateral neostriatum was retrogradely labelled with horseradish peroxidase. Quantitative estimates in 1-micrometer plastic sections showed that 68.5% of 1011 neurons counted project to the substantia nigra.