To investigate whether abnormal CD200-CD200R signalling could exacerbate microglial activation and dopaminergic neurodegneration in the 6-OHDA-induced rat PD model, we needed to find a proper dose of 6-OHDA that would produce only a limited loss of TH-ir neurons on the ipsilateral side of the SN. Here, CD200R1 is linked to Parkinson disease.