title: Embryonic ventral mesencephalic grafts improve levodopa-induced dyskinesia in a rat model of Parkinson's disease.
abstract: We investigated the role of dopamine neurons in the manifestation of levodopa-induced dyskinesia in a rat model of Parkinson's disease. Daily treatment with a subthreshold dose of levodopa gradually induced abnormal involuntary movements (AIM) in 6-hydroxydopamine-lesioned rats, which included stereotypy and contraversive rotation. After 4 weeks of levodopa treatment, rats with mild and severe AIM were assigned to two treatment subgroups. The graft subgroup received embryonic ventral mesencephalic tissue into the striatum, whilst the sham-graft subgroup received vehicle only. Rats continued to receive levodopa treatment for 3 months post-graft. Brain sections at the level of the basal ganglia were processed for autoradiography using a ligand for dopamine transporter, and in situ hybridization histochemistry for mRNAs encoding postsynaptic markers. Levodopa-induced AIM significantly improved in grafted rats. The severity of AIM correlated inversely with the density of dopamine nerve terminals in the striatum (P < 0. 001), with almost no AIM when the density of dopamine nerve terminals was >10-20% of normal. Embryonic dopamine neuronal grafts normalized not only mRNA expression for preproenkephalin (PPE) in the indirect pathway, but also mRNA expression for prodynorphin (PDyn) in the direct pathway, which was upregulated by levodopa treatment. AIM scores correlated linearly with expression of PPE mRNA in the indirect pathway (P < 0.001) and also with PDyn mRNA in the direct pathway (P < 0.001). We conclude that embryonic dopamine neuronal grafts may improve levodopa-induced dyskinesia by restoring altered activities of postsynaptic neurons, resulting not only from dopamine denervation, but also from levodopa therapy, provided that the density of striatal dopaminergic nerve terminals is restored above a 'threshold' level.
authors.affiliation: Neurodegenerative Disorders Centre, Vancouver Hospital and Health Sciences Centre, Vancouver, Canada. cslee@interchange.ubc.ca
authors.forename: C S
authors.initials: CS
authors.lastname: Lee
authors.forename: M A
authors.initials: MA
authors.lastname: Cenci
authors.forename: M
authors.initials: M
authors.lastname: Schulzer
authors.forename: A
authors.initials: A
authors.lastname: Björklund
mesh_terms: D000818:Animals; D000978:Antiparkinson Agents; D001345:Autoradiography; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D016380:Brain Tissue Transplantation / Q000502:physiology*; D004298:Dopamine / Q000502:physiology; D004409:Dyskinesia, Drug-Induced / Q000473:pathology / Q000628:therapy*; D005260:Female; D016332:Fetal Tissue Transplantation / Q000502:physiology*; D006892:Hydroxydopamines; D007091:Image Processing, Computer-Assisted; D017403:In Situ Hybridization; D007980:Levodopa; D008636:Mesencephalon / Q000473:pathology / Q000637:transplantation*; D017072:Neostriatum / Q000473:pathology / Q000601:surgery; D009411:Nerve Endings / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010302:Parkinson Disease, Secondary / Q000139:chemically induced / Q000473:pathology / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013566:Sympathomimetics
chemical_list: D000978:Antiparkinson Agents; D006892:Hydroxydopamines; D013566:Sympathomimetics; D007980:Levodopa; D004298:Dopamine