Although the ultimate target of infection is the central nervous system (CNS), there is evidence that the enteric nervous system (ENS) and the peripheral nervous system (PNS) are involved in the pathogenesis of orally communicated transmissible spongiform encephalopathies. In several peripherally challenged rodent models of scrapie, spread of infectious agent to the brain and spinal cord shows a pattern consistent with propagation along nerves supplying the viscera. We used immunocytochemistry (ICC) and paraffin-embedded tissue (PET) blotting to identify the location and temporal sequence of pathological accumulation of a host protein, PrP, in the CNS, PNS, and ENS of hamsters orally infected with the 263K scrapie strain. Enteric ganglia and components of splanchnic and vagus nerve circuitry were examined along with the brain and spinal cord. Bioassays were carried out with selected PNS constituents. Deposition of pathological PrP detected by ICC was consistent with immunostaining of a partially protease-resistant form of PrP (PrP Sc ) in PET blots. PrP Sc could be observed from approximately one-third of the way through the incubation period in enteric ganglia and autonomic ganglia of splanchnic or vagus circuitry prior to sensory ganglia. PrP Sc accumulated, in a defined temporal sequence, in sites that accurately reflected known autonomic and sensory relays. Scrapie agent infectivity was present in the PNS at low or moderate levels. The data suggest that, in this scrapie model, the infectious agent primarily uses synaptically linked autonomic ganglia and efferent fibers of the vagus and splanchnic nerves to invade initial target sites in the brain and spinal cord.

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Scrapie, a naturally-occurring disease of sheep, is the most studied member of a group of transmissible, neurodegenerative diseases known as transmissible spongiform encephalopathies (TSE) or prion diseases. The group includes BSE of cattle and CJD of man. Although the ultimate target of TSE infection is the CNS, the peripheral nervous system (PNS) appears to play a fundamental role in pathogenesis. I n several peripherally-infected rodent models of scrapic, spread of infection to the brain and spinal cord shows a pattern consistent with transit along nerves supplying the viscera. We used immunocytochemistry t o identify the location and temporal sequence of pathological accumulations of a host protein PrP, in the C N S and PNS of hamsters orally challenged with 263K scrapie. Specific PNS components of vagal o r splanchnic nerves were examined along with brain and spinal cord with which they form relay circuits. Enteric ganglia were included as potential early sites for infection. Results showed that pathological PrP accumulated in sequence, in target sites that accurately reflected known autonomic and sensory relays. Deposition was seen in cnteric, sympathetic and parasympathetic ganglia prior to sensory ganglia. These findings suggest that, in this scrapie model, after uptake from the gastrointestinal tract, the infectious agent primarily uses synaptically-linked autonomic ganglia and efferent fibres of the splanchnic and vagus nerves to reach C N S target sites.The folding and refolding of the recombinant Syrian hamster prion protein, SHaPrP(90-231), was studied using the fluorescence of the two tryptophan residues, Trp99 and Trp145. These residues are solvent-exposed and, consequently, the fluorescence changes associated with folding and unfolding transitions of PrP are very small. Thus, to enhance the fluorescence of PrP for folding studies a Trp mutant was engineered replacing a phenylalanine at position 198 (F198W). This mutant has a fluorescence signal 3-fold higher than the wild-type protein. Circular dichroism and Fourier transform infrared (FTIR) spectroscopy showed that F198W has the same fold as the wild-type PrP. Equilibrium unfolding and refolding studies in guanidine hydrochloride (GuHCI) demonstrated that the variant F198W is as stable as the wild-type protein. Both wild-type PrP and F198W variant show a two-state transition during GuHCI-induced folding and unfolding experiments. Equilibrium folding and unfoldingRecombinant Syrian hamster prion protein, SHaPrP(90-231) can be refolded in a predominantly a-helical conformation (a-PrP) or a form richer in p-sheet structure (p-PrP). The binding of a-and p-PrP to model lipid membranes was investigated by tryptophan fluorescence and surface plasmon resonance spectroscopy. Membranes composed of negatively charged or zwitterionic lipids, and raft-like membranes containing DPPC, cholesterol and sphingomyelin, were studied. We found that a-PrP binds to negatively charged lipid membranes and results in a membraneinserted conformation of PrP richer in P-shee...