Introduction: Levodopa-induced dyskinesia (LID) is an inevitable complication of the long-term treatment of Parkinson's disease (PD) with levodopa. In a rat model of LID, we observed that animals of almost identical genetic but slightly different environmental backgrounds displayed a very different profile in terms of their development and severity of LID.
Materials and methods: We hypothesised that this heterogeneity can be attributed to different levels of anxiety in individual animals. We evaluated the basal anxiety level of rats in this study using the elevated plus maze (EPM), open field (OF) test, and plasma corticosterone level. These animals then received unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway after which they were primed to develop LID. Finally, we manipulated the anxiety level of these animals by citalopram treatment over a 9-week period before they were killed.
Results: Although we could not establish an association between the anxiety level of rats with either the onset or severity of LID, our results showed that citalopram was able to mediate a partial alleviation in LID after chronic treatment, and the extent of recovery was negatively correlated to the anxiety measures of individual animals. Furthermore, this citalopram-mediated LID recovery appeared to be independent of any changes in striatal cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) and cyclin-dependent kinase 5 (Cdk5) system, in contrast to our previous studies with fetal ventral mesencephalon transplants. However, chronic citalopram treatment almost completely abolished the expression of serotonin receptor 1B (5HT1B) in the striatum in animals exhibiting LID recovery.
Conclusions: These results indicate a novel association of serotonin receptors in the development of LID and contributes to the evidence that the serotonergic system may play an important role in such movements.