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: In this respect , little is known about the role of DA receptors in the occurrence of epilepsy - induced neuronal cell death .
### Output Text:
In this respect , little is known about the role of <span class="chemical">DA</span> receptors in the occurrence of epilepsy - induced neuronal cell death . 