View point: etiology in Parkinson's disease. Dual hit or spreading intoxication

Parkinson's disease is not only a movement disorder: non-motor symptoms such as loss of smell, constipation, depression, cognitive impairment, sleep problems and disturbances of the autonomic nervous system also feature. The etiology is still unknown, although an increasing number of gene-related Parkinsonian syndromes have been identified. It is intriguing to speculate that PD starts by the intake of a toxin, bacteria or virus. This idea stems from the fact that pathological abnormalities such as Lewy neuritis, Lewy bodies and alpha-synuclein accumulation are first found in the enteric nervous system of the gut and in the olfactory bulb. There is increasing evidence that the disease may spread out from the enteric nervous system of the gut via the vagal nerve up to the brain. Here we present data from animal work which supports this assumption.