Origin of the climbing fibers activated by glossopharyngeal nerve stimulation in the frog.

The origin of climbing fibers activated by electrical stimulation of the frog's glossopharyngeal (IXth) nerve was investigated using histological and electrophysiological technique. At the molecular layer near the Purkinje cell layer, where the maximum negative cerebellar field potential could be recorded following electrical stimulation of the IXth nerve, horseradish peroxidase (HRP) was iontophoretically injected through the tip of the recording micropipette. The HRP labeled cells were seen in the contralateral inferior olive (IO). In some cases, a small number of HRP-labeled cells were seen in the ipsilateral IO. Labeled cells were not found in the other areas of the brain stem. After electrolytic lesion of the contralateral IO, the negative cerebellar field potential which would be recorded in the molecular layer following electrical stimulation of the IXth nerve had almost ceased. These results demonstrate that the climbing fibers activated by the IXth nerve stimulation have their origin in the contralateral IO.