Minocycline inhibits microglial activation and protects nigral cells after 6-hydroxydopamine injection into mouse striatum

To determine the role of immune/inflammatory factors in dopaminergic cell degeneration in parkinsonian substantia nigra, we assayed tyrosine hydroxylase (TH)-positive immunoreactive neuronal numbers with stereologic techniques and CD11b-positive immunoreactive microglial profiles following 6-hydroxydopamine (6-OHDA) injection into ipsilateral striatum of mice. We further investigated the effect of minocycline on the inhibition of microglial activation and subsequent protection of nigral cells. The relative number of microglial profiles in the substantia nigra (SN) ipsilateral to the injection increased from 31 to 32% 1-3 days after injection, and increased further to 55% by 7 days and 59% by 14 days, compared with the contralateral SN. These changes started prior to the decrease of TH immunoreactivity of 34% on day 7 and of 42% by day 14. In animals treated with minocycline, microglial activation was inhibited by 47%, and TH positive cells were protected by 21% at day 14 after 6-OHDA injection, compared with those parkinsonian animals without minocycline treatment. All these results suggest that microglial activation may be involved in the nigral cell degeneration in 6-OHDA induced parkinsonian mice.