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: Dopamine ( DA ) , through D1 / D2 receptor - mediated signaling , plays a major role in the control of epileptic seizures arising in the limbic system .
### Output Text:
<span class="chemical">Dopamine</span> ( <span class="chemical">DA</span> ) , through D1 / D2 receptor - mediated signaling , plays a major role in the control of epileptic seizures arising in the limbic system . 