In 6-OHDA PD models, the tyrosine hydroxylase (TH) immunoreactivity in DMV neurons is significantly increased; however, the expression of choline acetyltransferase (ChAT, a marker of cholinergic neurons) is decreased, the Ach content is reduced in the gastric muscular layer, and gastric emptying is delayed [14]. Here, TH is linked to Parkinson disease.