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: Moreover calcitonin induced a significant decrease in nigral GAD activity but no change in striatal DA and DOPAC concentration or GAD activity .
### Output Text:
Moreover calcitonin induced a significant decrease in nigral GAD activity but no change in striatal <span class="chemical">DA</span> and <span class="chemical">DOPAC</span> concentration or GAD activity . 