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: Subjects received the tonically stimulating dopamine - receptor agonist pergolide ( 0 . 1 mg ) vs placebo 120 min before training on each training day .
### Output Text:
Subjects received the tonically stimulating <span class="chemical">dopamine</span> - receptor agonist <span class="chemical">pergolide</span> ( 0 . 1 mg ) vs placebo 120 min before training on each training day . 