In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Because the CNS damage caused by METH and MPTP is highly selective for the DA neuronal system in mouse models of neurotoxicity , we hypothesized that the CX3CR1 plays a role in METH - induced neurotoxicity and microglial activation .
### Output Text:
Because the CNS damage caused by <span class="chemical">METH</span> and <span class="chemical">MPTP</span> is highly selective for the <span class="chemical">DA</span> neuronal system in mouse models of neurotoxicity , we hypothesized that the CX3CR1 plays a role in <span class="chemical">METH</span> - induced neurotoxicity and microglial activation . 