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: They offer protection against seizures in a range of models and seem to inhibit certain stages of drug dependence in preclinical assessments .
### Output Text:
They offer protection against seizures in a range of models and seem to inhibit certain stages of drug dependence in preclinical assessments . 