124.3 (3.9)] compared to the non-Mn miners [113.1 (5.1)] (p = 0.11). Mn miners had lower mean (standard error) neuron density in the caudate [203.1(24.9) cells per high powered field (hpf)] compared to non-Mn miners [276.9 (22.3) cells per hpf] (p = 0.016). Mn miners also had lower astrocyte density in the caudate [181 (22.0) cells per hpf] and putamen [225.6 (28.5) cells per hpf] than non Mn miners [caudate 252 .9 (19.6) cells per hpf and putamen 300.9 (25.4) cells per hpf] (p = 0.011 and p =

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... .024, respectively). There were no significant differences in microglial cell density or in astrocyte, microglia or neuron cell counts in the globus pallidus between the two groups. There were no HIV-defining pathologies and no microglial nodules in any of the miners. Conclusions This study demonstrates that chronic Mn exposure is associated with selective toxicity to striatal astrocytes and caudate neurons. We speculate that the initial neurotoxic injury in humans with chronic Mn exposure involves the astrocytes and that neuronal injury may be secondary to loss of astrocytes.