Labelling of cerebellar mossy fiber afferents with intra-axonal horseradish peroxidase.

Several unidentified units recorded in the intermediate zone of lobules IV and V of the cerebellar cortex responded to superficial radial nerve stimulation with a distinctive short train of 5 to 11 low amplitude spikes (less than 5 mV) at a frequency of 800 to 1200 Hz. Responses of this type have in the past been attributed to mossy fiber afferents. Following the electrophysiological characterization horseradish peroxidase was successfully injected by iontophoresis into four axon terminals. The labelled axons presented the typical structure of mossy fibers with terminal rosettes and corresponded to the morphology of these axons described in Golgi material.