SLC6A4 and Parkinson disease: In addition, the increase of alpha-synuclein (a-syn) levels, the major component of the typical aggregates found in PD, is associated with a reduction in 5-HT levels in selective hippocampal sub-regions (DG/CA3) and intense growth of SERT+ fibers projecting into the DG, indicating the presence of dystrophic hippocampal SERT+ fibers in this PD model [173].