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: The results indicate that , in this model , a subpopulation of GAD mRNA - containing neurons within the dentate gyrus is selectively vulnerable to seizure - induced damage .
### Output Text:
The results indicate that , in this model , a subpopulation of GAD mRNA - containing neurons within the dentate gyrus is selectively vulnerable to seizure - induced damage . 