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: Growth - associated protein 43 expression in hippocampal molecular layer of chronic epileptic rats treated with cycloheximide .
### Output Text:
Growth - associated protein 43 expression in hippocampal molecular layer of chronic epileptic rats treated with <span class="chemical">cycloheximide</span> . 