TNF and Parkinson disease: TNF and ceramide have been shown to impinge on endoplasmic reticulum (ER) stress mechanisms in non-neuronal cells types [40,41] and ER stress has been implicated as a potentially important pathway in neurodegenerative diseases [60]; however, whether ER stress is a cause, result, or epiphenomenon in the DA neuron loss that occurs in PD has not been firmly established.