alpha 4 beta 2 nicotinic receptors play a role in the nAChR-mediated decline in l-dopa-induced dyskinesias in parkinsonian rats

• Published in: Neuropharmacology 2013-08, Vol.71, p.191-203
• Main Authors: Quik, Maryka, Campos, Carla, Bordia, Tanuja, Strachan, Jon-Paul, Zhang, Jenny, McIntosh, JMichael, Letchworth, Sharon, Jordan, Kristen
• Format: Article
• Language: English
• ISSN: 0028-3908
• DOI: 10.1016/j.neuropharm.2013.03.038

l-dopa-induced dyskinesias are a serious long-term side effect of dopamine replacement therapy for Parkinson's disease for which there are few treatment options. Our previous studies showed that nicotine decreased l-dopa-induced abnormal involuntary movements (AIMs). Subsequent work with knockout mice demonstrated that alpha 6 beta 2* nicotinic receptors (nAChRs) play a key role. The present experiments were done to determine if alpha 4 beta 2* nAChRs are also involved in l-dopa-induced dyskinesias. To approach this, we took advantage of the finding that alpha 6 beta 2* nAChRs are predominantly present on striatal dopaminergic nerve terminals, while a significant population of alpha 4 beta 2* nAChRs are located on other neurons. Thus, a severe dopaminergic lesion would cause a major loss in alpha 6 beta 2*, but not alpha 4 beta 2* nAChRs. Experiments were therefore done in which rats were unilaterally lesioned with 6-hydroxydopamine, at a dose that led to severe nigrostriatal damage. The dopamine transporter, a dopamine nerve terminal marker, was decreased by >99%. This lesion also decreased striatal alpha 6 beta 2* nAChRs by 97%, while alpha 4 beta 2* nAChRs were reduced by only 12% compared to control. A series of beta 2* nAChR compounds, including TC-2696, TI-10165, TC-8831, TC-10600 and sazetidine reduced l-dopa-induced AIMs in these rats by 23-32%. TC-2696, TI-10165, TC-8831 were also tested for parkinsonism, with no effect on this behavior. Tolerance did not develop with up to 3 months of treatment. Since alpha 4 alpha 5 beta 2 nAChRs are also predominantly on striatal dopamine terminals, these data suggest that drugs targeting alpha 4 beta 2 nAChRs may reduce l-dopa-induced dyskinesias in late stage Parkinson's disease.