NTRK1 and Alzheimer disease: Nevertheless, it did not affect clinical outcomes of biomarkers in Alzheimer's disease,51 probably because of the TrkA downregulation in cholinergic neurons that has been reported in several Alzheimer's disease studies.6 Cholinergic neurons express two types of NGF receptors, including TrkA that induces cell survival and pNTR75 that induces cell death.