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 situ hybridization methods were used to determine if glutamic acid decarboxylase ( GAD ) mRNA - containing neurons within the hilus of the dentate gyrus are vulnerable to seizure - induced damage in a model of chronic seizures .
### Output Text:
In situ hybridization methods were used to determine if <span class="chemical">glutamic acid</span> decarboxylase ( GAD ) mRNA - containing neurons within the hilus of the dentate gyrus are vulnerable to seizure - induced damage in a model of chronic seizures . 