SHH and Parkinson disease: In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced in vivo model of Parkinson’s disease, activated microglia were found to express Shh, and most neural cells, except oligodendrocytes, responded to microglia-derived Shh in MPTP-treated substantia nigra [42].