The ratio of M1 to M2 microglia in the striatum determines the severity of L‐Dopa‐induced dyskinesias

Abstract

AbstractL‐Dopa, while treating motor symptoms of Parkinson's disease, can lead to debilitating L‐Dopa‐induced dyskinesias, limiting its use. To investigate the causative relationship between neuro‐inflammation and dyskinesias, we assessed if striatal M1 and M2 microglia numbers correlated with dyskinesia severity and whether the anti‐inflammatories, minocycline and indomethacin, reverse these numbers and mitigate against dyskinesia. In 6‐OHDA lesioned mice, we used stereology to assess numbers of striatal M1 and M2 microglia populations in non‐lesioned (naïve) and lesioned mice that either received no L‐Dopa (PD), remained non‐dyskinetic even after L‐Dopa (non‐LID) or became dyskinetic after L‐Dopa treatment (LID). We also assessed the effect of minocycline/indomethacin treatment on striatal M1 and M2 microglia and its anti‐dyskinetic potential via AIMs scoring. We report that L‐Dopa treatment leading to LIDs exacerbates activated microglia numbers beyond that associated with the PD state; the severity of LIDs is strongly correlated to the ratio of the striatal M1 to M2 microglial numbers; in non‐dyskinetic mice, there is no M1/M2 microglia ratio increase above that seen in PD mice; and reducing M1/M2 microglia ratio using anti‐inflammatories is anti‐dyskinetic. Parkinson's disease is associated with increased inflammation, but this is insufficient to underpin dyskinesia. Given that L‐Dopa‐treated non‐LID mice show the same ratio of M1/M2 microglia as PD mice that received no L‐Dopa, and, given minocycline/indomethacin reduces both the ratio of M1/M2 microglia and dyskinesia severity, our data suggest the increased microglial M1/M2 ratio that occurs following L‐Dopa treatment is a contributing cause of dyskinesias.