VIP and Parkinson disease: Stage 1: The first PD pathological findings almost always appear with the formation of isolated scattered Lewy neurites at the dorsal motor nucleus of the vagus nerve, adjoining intermediate reticular zone, olfactory bulb, anterior olfactory nucleus, and vasoactive intestinal peptide (VIP) secreting neurons within the enteric nervous system, with complete sparing of solitary and ambiguous nuclei of the vagus nerve [41].