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: Effects of the antidepressant trazodone , a 5 - HT 2A / 2C receptor antagonist , on dopamine - dependent behaviors in rats .
### Output Text:
Effects of the antidepressant <span class="chemical">trazodone</span> , a <span class="chemical">5 - HT</span> 2A / 2C receptor antagonist , on <span class="chemical">dopamine</span> - dependent behaviors in rats . 