title: Melatonin reduces the neuronal loss, downregulation of dopamine transporter, and upregulation of D2 receptor in rotenone-induced parkinsonian rats.
abstract: Parkinson's disease (PD) is a movement disorder resulting from nigrostriatal dopaminergic neurodegeneration. The impairment of mitochondrial function and dopamine synaptic transmission are involved in the pathogenesis of PD. Two mitochondrial inhibitors, 1-methyl-4-phenylpyridine (MPP(+)) and rotenone, have been used to induce dopaminergic neuronal death both in in vitro and in vivo models of PD. Because the uptake of MPP(+) is mediated by the dopamine transporter (DAT), we used a cell-permeable rotenone-induced PD model to investigate the role of DAT and dopamine D2 receptor (D2R) on dopaminergic neuronal loss. Rotenone subcutaneously infused for 14 days induced PD symptoms in rats, as indicated by reduced spontaneous locomotor activity (hypokinesis), loss of tyrosine hydroxylase (TH, a marker enzyme for dopamine neurons) immunoreactivity in the substantia nigra and striatum, obvious alpha-synuclein accumulation, downregulated DAT protein expression, and upregulated D2R expression. Interestingly, rotenone also caused significant noradrenergic neuronal loss in the locus coeruleus. Melatonin, an antioxidant, prevented nigrostriatal neurodegeneration and alpha-synuclein aggregation without affecting the rotenone-induced weight loss and hypokinesis. However, rotenone-induced hypokinesis was markedly reversed by the DAT antagonist nomifensine and body weight loss was attenuated by the D2R antagonist sulpiride. In addition, both antagonists significantly prevented the reduction of striatal TH or DAT immunoreactivity but not the loss of nigral TH- and DAT-immunopositive neurons. These results suggested that oxidative stress and DAT downregulation are involved in the rotenone-induced pathogenesis of nigrostriatal dopaminergic neurodegeneration, whereas D2R upregulation may simply represent a compensatory response.
authors.affiliation: Department of Physiology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Chun-Hung
authors.initials: CH
authors.lastname: Lin
authors.forename: Jui-Yen
authors.initials: JY
authors.lastname: Huang
authors.forename: Cheng-Hsin
authors.initials: CH
authors.lastname: Ching
authors.forename: Jih-Ing
authors.initials: JI
authors.lastname: Chuang
mesh_terms: D000818:Animals; D002452:Cell Count; D004195:Disease Models, Animal; D050483:Dopamine Plasma Membrane Transport Proteins / Q000037:antagonists & inhibitors*; D015536:Down-Regulation / Q000187:drug effects*; D008550:Melatonin / Q000627:therapeutic use*; D020734:Parkinsonian Disorders / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000096:biosynthesis* / Q000235:genetics; D012402:Rotenone; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D017448:Receptors, Dopamine D2; D012402:Rotenone; D008550:Melatonin