Animal models of PD have been often used to test the efficacy of vitamin D in the disease pathology in terms of dopamine production, neurotrophic factors synthesis, as well as the possible neuroprotective effect of vitamin D. In a rat model of PD, intraperitoneal injection of 1,25(OH)2D3 before or after inducing PD partially restored tyrosine hydroxylase expression in the substantia nigra [146] thus promoting the conversion of tyrosine to dopamine. This evidence concerns the gene TH and Parkinson disease.