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 concentration of dopamine was increased in the mesencephalon and that of its metabolite DOPAC was also increased in the mesencephalon and the striatum .
### Output Text:
The concentration of <span class="chemical">dopamine</span> was increased in the mesencephalon and that of its metabolite <span class="chemical">DOPAC</span> was also increased in the mesencephalon and the striatum . 