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: Blockade of both D - 1 and D - 2 dopamine receptors may induce catalepsy in mice .
### Output Text:
Blockade of both D - 1 and D - 2 <span class="chemical">dopamine</span> receptors may induce catalepsy in mice . 