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: The results of this study suggest that the blockade of mGluR5 by MPEP may protect dopaminergic neurones against methamphetamine - induced toxicity .
### Output Text:
The results of this study suggest that the blockade of mGluR5 by <span class="chemical">MPEP</span> may protect dopaminergic neurones against <span class="chemical">methamphetamine</span> - induced toxicity . 