Enteroglial and neuronal involvement without apparent neuron loss in ileal enteric nervous system plexuses from scrapie-affected sheep

The enteric nervous system (ENS) probably plays a dominant role in sheep scrapie pathogenesis, but little is known about the cell types involved. We investigated the ileal myenteric and submucosal plexuses of four naturally and four orally experimentally scrap i e-affected ARQ/ARQ Sarda sheep, as well as those of 12 healthy-control Sarda sheep carrying different PrP genotypes. All scrapie-affected animals, euthanized at clinical-disease end stage, showed PrPd deposition within enteric glial cells (EGCs) and calbindin-immunoreactive (CALB-IR) and neuronal nitric oxide synthase (nNOS)-IR neurons. Whole-mount investigations revealed no significant differences between the densities of total, CALB-IR and nNOS-IR neurons in scrapie-affected versus healthy sheep, irrespective of PrP genotype. Our results suggest that EGCs and CALB-IR and nNOS-IR neurons are probably involved in the pathogenesis of natural and oral experimental sheep scrapie. Furthermore, the infectious agent may be less pathogenic towards ENS neurons than it is towards central nervous system neurons.