Detection of the Abnormal Isoform of the Prion Protein Associated With Chronic Wasting Disease in the Optic Pathways of the Brain and Retina of Rocky Mountain Elk (Cervus elaphus nelsoni)

Authors

T. R. Spraker, Colorado State University - Fort Collins
Katherine I. O'Rourke, U.S. Department of AgricultureFollow
T. Gidlewski, U.S. Department of AgricultureFollow
J. G. Powers, National Park Service
J. J. Greenlee, U.S. Department of Agriculture
M. A. Wild, National Park Service

Document Type

Article

Date of this Version

2010

Comments

Published in Veterinary Pathology 47(3) 536-546 (2010)

Abstract

Eyes and nuclei of the visual pathways in the brain were examined in 30 Rocky Mountain elk (Cervus elaphus nelsoni) representing 3 genotypes of the prion protein gene PRNP (codon 132: MM, ML, or LL). Tissues were examined for the presence of the abnormal isoform of the prion protein associated with chronic wasting disease (PrP^CWD). Nuclei and axonal tracts from a single section of brain stem at the level of the dorsal motor nucleus of the vagus nerve were scored for intensity and distribution of PrP^CWD immunoreactivity and degree of spongiform degeneration. This obex scoring ranged from 0 (elk with no PrP^CWD in the brain stem) to 10 (representing elk in terminal stage of disease). PrP^CWD was detected in the retina of 16 of 18 (89%) elk with an obex score of > 7. PrP^CWD was not detected in the retina of the 3 chronic wasting disease–negative elk and 9 elk with an obex score of < 6. PrP^CWD was found in the nuclei of the visual pathways in the brain before it was found in the retina. Within the retina, PrP^CWD was first found in the inner plexiform layer, followed by the outer plexiform layer. Intracytoplasmic accumulation of PrP^CWD was found in a few neurons in the ganglion cell layer in the PRNP 132ML elk but was a prominent feature in the PRNP 132LL elk. Small aggregates of PrP^CWD were present on the inner surface of the outer limiting membrane in PRNP 132LL elk but not in PRNP 132MM or 132ML elk. This study demonstrates PrP^CWD accumulation in nuclei of the visual pathways of the brain, followed by PrP^CWD in the retina.