Diffusion of horseradish peroxidase at the injection site.

The sensitivity of diaminobenzidine (DAB), tetramethylbenzidine (TMB) and Hanker-Yates (H-Y) methods was compared in order to determine which procedure shows best the effective site of horseradish peroxidase (HRP) uptake. The lateral geniculate nucleus was chosen as the target nucleus for HRP injections, and the neuronal labelling in the superior colliculus and in zona incerta was used as a control. While TMB showed images that overestimated the effective site of uptake, the H-Y procedure showed more restricted HRP spots, similar to those obtained with DAB, that corresponded well with the neuronal labelling observed in the control areas. These results underline the usefulness of the H-Y procedure upon evaluation of the effective site of uptake. In addition, they do not support an underestimation of this effective site by this method.