Differences in extrinsic innervation patterns of the small intestine in the cattle and sheep.

After oral challenge of the pathological prion protein, the pathogen was first detected in the distal ileum and then deposited in the brain. The present study aims determining the possible neuronal transport pathways from the small intestine to the brain in the cattle and sheep using a tracer protein. After horseradish peroxidase was injected into the wall in the duodenum of the calf and lamb and in the ileum of the lamb, the greater part of labeled neurons was detected in the celiac and cranial mesenteric ganglion complex. In the dorsal root ganglia T3 to L4 of both animals, some sensory neurons were always found to be labeled. Some parasympathetic preganglionic neurons were labeled in the dorsal motor nucleus of the vagus nerve after injections into the duodenum of the cattle and sheep, but extremely a small number of them were labeled after ileal application. The number of labeled sensory neurons in the nodose ganglion after duodenal injections of the sheep was much greater than that after duodenal application of the cattle. After ileal injections in the sheep, practically no labeled sensory neurons were found in the nodose ganglion. These results suggest that the pathological prion protein is mainly transported to the spinal cord and brain via the sympathetic nervous system and partially via the sensory neurons in the dorsal root ganglia. The vagus nerve seems to contribute to the transport of the pathogen not from the ileum, but from the duodenum.