Brain targeting through the autonomous nervous system: lessons from prion diseases.

The human central nervous system (CNS) is targeted by diverse pathogens that use distinct pathways to bypass the blood-brain barrier, such as trafficking into the brain via infected blood cells or using retrograde axonal transport through sensory or motor fibers. Prions are transmissible agents that induce a devastating subacute neurodegeneration when they successfully reach the CNS. Two recent studies focusing on pathways of prion neuroinvasion provide converging evidence that, in the case of peripheral transmission, such as human consumption of contaminated tissue, the infectious agent uses the sympathetic noradrenergic neurons to reach the CNS after early replication in lymphoid tissues.