Studies on cytokines and neurotrophins in the postmortem brain of experimental PD animals with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine or 6-hydroxy dopamine found higher levels of pro-inflammatory cytokines like TNF-α as well as decreased levels of neurotrophins like BDNF in the nigrostriatal regions [40]. Here, TNF is linked to Parkinson disease.