The absence of horseradish peroxidase uptake by cerebellar afferents to the red nucleus of the cat.

Horseradish peroxidase (HRP) administered to the red nucleus (RN) failed to be transported retrogradely in the axons of the cerebellorubral projection system. This negative result was independent of the anaesthesia, fixation method, injection time or survival period. The absence of HRP uptake and transport in our work reflects some uncertainty in the general usefulness of the HRP technique.