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: MPEP administered into the striatum at high concentrations ( 500 microM ) increased extracellular dopamine levels , while lower concentrations ( 50 - 100 microM ) were devoid of any effect .
### Output Text:
<span class="chemical">MPEP</span> administered into the striatum at high concentrations ( 500 microM ) increased extracellular <span class="chemical">dopamine</span> levels , while lower concentrations ( 50 - 100 microM ) were devoid of any effect . 